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dsa.c
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1/*-------------------------------------------------------------------------
2 *
3 * dsa.c
4 * Dynamic shared memory areas.
5 *
6 * This module provides dynamic shared memory areas which are built on top of
7 * DSM segments. While dsm.c allows segments of memory of shared memory to be
8 * created and shared between backends, it isn't designed to deal with small
9 * objects. A DSA area is a shared memory heap usually backed by one or more
10 * DSM segments which can allocate memory using dsa_allocate() and dsa_free().
11 * Alternatively, it can be created in pre-existing shared memory, including a
12 * DSM segment, and then create extra DSM segments as required. Unlike the
13 * regular system heap, it deals in pseudo-pointers which must be converted to
14 * backend-local pointers before they are dereferenced. These pseudo-pointers
15 * can however be shared with other backends, and can be used to construct
16 * shared data structures.
17 *
18 * Each DSA area manages a set of DSM segments, adding new segments as
19 * required and detaching them when they are no longer needed. Each segment
20 * contains a number of 4KB pages, a free page manager for tracking
21 * consecutive runs of free pages, and a page map for tracking the source of
22 * objects allocated on each page. Allocation requests above 8KB are handled
23 * by choosing a segment and finding consecutive free pages in its free page
24 * manager. Allocation requests for smaller sizes are handled using pools of
25 * objects of a selection of sizes. Each pool consists of a number of 16 page
26 * (64KB) superblocks allocated in the same way as large objects. Allocation
27 * of large objects and new superblocks is serialized by a single LWLock, but
28 * allocation of small objects from pre-existing superblocks uses one LWLock
29 * per pool. Currently there is one pool, and therefore one lock, per size
30 * class. Per-core pools to increase concurrency and strategies for reducing
31 * the resulting fragmentation are areas for future research. Each superblock
32 * is managed with a 'span', which tracks the superblock's freelist. Free
33 * requests are handled by looking in the page map to find which span an
34 * address was allocated from, so that small objects can be returned to the
35 * appropriate free list, and large object pages can be returned directly to
36 * the free page map. When allocating, simple heuristics for selecting
37 * segments and superblocks try to encourage occupied memory to be
38 * concentrated, increasing the likelihood that whole superblocks can become
39 * empty and be returned to the free page manager, and whole segments can
40 * become empty and be returned to the operating system.
41 *
42 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
43 * Portions Copyright (c) 1994, Regents of the University of California
44 *
45 * IDENTIFICATION
46 * src/backend/utils/mmgr/dsa.c
47 *
48 *-------------------------------------------------------------------------
49 */
50
51#include "postgres.h"
52
53#include "port/atomics.h"
54#include "port/pg_bitutils.h"
55#include "storage/dsm.h"
56#include "storage/lwlock.h"
57#include "utils/dsa.h"
58#include "utils/freepage.h"
59#include "utils/memutils.h"
60#include "utils/resowner.h"
61
62/*
63 * How many segments to create before we double the segment size. If this is
64 * low, then there is likely to be a lot of wasted space in the largest
65 * segment. If it is high, then we risk running out of segment slots (see
66 * dsm.c's limits on total number of segments), or limiting the total size
67 * an area can manage when using small pointers.
68 */
69#define DSA_NUM_SEGMENTS_AT_EACH_SIZE 2
70
71/*
72 * The maximum number of DSM segments that an area can own, determined by
73 * the number of bits remaining (but capped at 1024).
74 */
75#define DSA_MAX_SEGMENTS \
76 Min(1024, (1 << ((SIZEOF_DSA_POINTER * 8) - DSA_OFFSET_WIDTH)))
77
78/* The bitmask for extracting the offset from a dsa_pointer. */
79#define DSA_OFFSET_BITMASK (((dsa_pointer) 1 << DSA_OFFSET_WIDTH) - 1)
80
81/* Number of pages (see FPM_PAGE_SIZE) per regular superblock. */
82#define DSA_PAGES_PER_SUPERBLOCK 16
83
84/*
85 * A magic number used as a sanity check for following DSM segments belonging
86 * to a DSA area (this number will be XORed with the area handle and
87 * the segment index).
88 */
89#define DSA_SEGMENT_HEADER_MAGIC 0x0ce26608
90
91/* Build a dsa_pointer given a segment number and offset. */
92#define DSA_MAKE_POINTER(segment_number, offset) \
93 (((dsa_pointer) (segment_number) << DSA_OFFSET_WIDTH) | (offset))
94
95/* Extract the segment number from a dsa_pointer. */
96#define DSA_EXTRACT_SEGMENT_NUMBER(dp) ((dp) >> DSA_OFFSET_WIDTH)
97
98/* Extract the offset from a dsa_pointer. */
99#define DSA_EXTRACT_OFFSET(dp) ((dp) & DSA_OFFSET_BITMASK)
100
101/* The type used for index segment indexes (zero based). */
102typedef size_t dsa_segment_index;
103
104/* Sentinel value for dsa_segment_index indicating 'none' or 'end'. */
105#define DSA_SEGMENT_INDEX_NONE (~(dsa_segment_index)0)
106
107/*
108 * How many bins of segments do we have? The bins are used to categorize
109 * segments by their largest contiguous run of free pages.
110 */
111#define DSA_NUM_SEGMENT_BINS 16
112
113/*
114 * What is the lowest bin that holds segments that *might* have n contiguous
115 * free pages? There is no point in looking in segments in lower bins; they
116 * definitely can't service a request for n free pages.
117 */
118static inline size_t
120{
121 size_t bin;
122
123 if (n == 0)
124 bin = 0;
125 else
126 bin = pg_leftmost_one_pos_size_t(n) + 1;
127
128 return Min(bin, DSA_NUM_SEGMENT_BINS - 1);
129}
130
131/* Macros for access to locks. */
132#define DSA_AREA_LOCK(area) (&area->control->lock)
133#define DSA_SCLASS_LOCK(area, sclass) (&area->control->pools[sclass].lock)
134
135/*
136 * The header for an individual segment. This lives at the start of each DSM
137 * segment owned by a DSA area including the first segment (where it appears
138 * as part of the dsa_area_control struct).
139 */
140typedef struct
141{
142 /* Sanity check magic value. */
144 /* Total number of pages in this segment (excluding metadata area). */
146 /* Total size of this segment in bytes. */
147 size_t size;
148
149 /*
150 * Index of the segment that precedes this one in the same segment bin, or
151 * DSA_SEGMENT_INDEX_NONE if this is the first one.
152 */
154
155 /*
156 * Index of the segment that follows this one in the same segment bin, or
157 * DSA_SEGMENT_INDEX_NONE if this is the last one.
158 */
160 /* The index of the bin that contains this segment. */
161 size_t bin;
162
163 /*
164 * A flag raised to indicate that this segment is being returned to the
165 * operating system and has been unpinned.
166 */
167 bool freed;
169
170/*
171 * Metadata for one superblock.
172 *
173 * For most blocks, span objects are stored out-of-line; that is, the span
174 * object is not stored within the block itself. But, as an exception, for a
175 * "span of spans", the span object is stored "inline". The allocation is
176 * always exactly one page, and the dsa_area_span object is located at
177 * the beginning of that page. The size class is DSA_SCLASS_BLOCK_OF_SPANS,
178 * and the remaining fields are used just as they would be in an ordinary
179 * block. We can't allocate spans out of ordinary superblocks because
180 * creating an ordinary superblock requires us to be able to allocate a span
181 * *first*. Doing it this way avoids that circularity.
182 */
183typedef struct
184{
185 dsa_pointer pool; /* Containing pool. */
186 dsa_pointer prevspan; /* Previous span. */
187 dsa_pointer nextspan; /* Next span. */
188 dsa_pointer start; /* Starting address. */
189 size_t npages; /* Length of span in pages. */
190 uint16 size_class; /* Size class. */
191 uint16 ninitialized; /* Maximum number of objects ever allocated. */
192 uint16 nallocatable; /* Number of objects currently allocatable. */
193 uint16 firstfree; /* First object on free list. */
194 uint16 nmax; /* Maximum number of objects ever possible. */
195 uint16 fclass; /* Current fullness class. */
197
198/*
199 * Given a pointer to an object in a span, access the index of the next free
200 * object in the same span (ie in the span's freelist) as an L-value.
201 */
202#define NextFreeObjectIndex(object) (* (uint16 *) (object))
203
204/*
205 * Small allocations are handled by dividing a single block of memory into
206 * many small objects of equal size. The possible allocation sizes are
207 * defined by the following array. Larger size classes are spaced more widely
208 * than smaller size classes. We fudge the spacing for size classes >1kB to
209 * avoid space wastage: based on the knowledge that we plan to allocate 64kB
210 * blocks, we bump the maximum object size up to the largest multiple of
211 * 8 bytes that still lets us fit the same number of objects into one block.
212 *
213 * NB: Because of this fudging, if we were ever to use differently-sized blocks
214 * for small allocations, these size classes would need to be reworked to be
215 * optimal for the new size.
216 *
217 * NB: The optimal spacing for size classes, as well as the size of the blocks
218 * out of which small objects are allocated, is not a question that has one
219 * right answer. Some allocators (such as tcmalloc) use more closely-spaced
220 * size classes than we do here, while others (like aset.c) use more
221 * widely-spaced classes. Spacing the classes more closely avoids wasting
222 * memory within individual chunks, but also means a larger number of
223 * potentially-unfilled blocks.
224 */
225static const uint16 dsa_size_classes[] = {
226 sizeof(dsa_area_span), 0, /* special size classes */
227 8, 16, 24, 32, 40, 48, 56, 64, /* 8 classes separated by 8 bytes */
228 80, 96, 112, 128, /* 4 classes separated by 16 bytes */
229 160, 192, 224, 256, /* 4 classes separated by 32 bytes */
230 320, 384, 448, 512, /* 4 classes separated by 64 bytes */
231 640, 768, 896, 1024, /* 4 classes separated by 128 bytes */
232 1280, 1560, 1816, 2048, /* 4 classes separated by ~256 bytes */
233 2616, 3120, 3640, 4096, /* 4 classes separated by ~512 bytes */
234 5456, 6552, 7280, 8192 /* 4 classes separated by ~1024 bytes */
235};
236#define DSA_NUM_SIZE_CLASSES lengthof(dsa_size_classes)
237
238/* Special size classes. */
239#define DSA_SCLASS_BLOCK_OF_SPANS 0
240#define DSA_SCLASS_SPAN_LARGE 1
241
242/*
243 * The following lookup table is used to map the size of small objects
244 * (less than 1kB) onto the corresponding size class. To use this table,
245 * round the size of the object up to the next multiple of 8 bytes, and then
246 * index into this array.
247 */
248static const uint8 dsa_size_class_map[] = {
249 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 11, 11, 12, 12, 13, 13,
250 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 17, 17, 17, 17,
251 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 19, 19, 19, 19,
252 20, 20, 20, 20, 20, 20, 20, 20, 21, 21, 21, 21, 21, 21, 21, 21,
253 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
254 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
255 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
256 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25
257};
258#define DSA_SIZE_CLASS_MAP_QUANTUM 8
259
260/*
261 * Superblocks are binned by how full they are. Generally, each fullness
262 * class corresponds to one quartile, but the block being used for
263 * allocations is always at the head of the list for fullness class 1,
264 * regardless of how full it really is.
265 */
266#define DSA_FULLNESS_CLASSES 4
267
268/*
269 * A dsa_area_pool represents a set of objects of a given size class.
270 *
271 * Perhaps there should be multiple pools for the same size class for
272 * contention avoidance, but for now there is just one!
273 */
274typedef struct
275{
276 /* A lock protecting access to this pool. */
278 /* A set of linked lists of spans, arranged by fullness. */
280 /* Should we pad this out to a cacheline boundary? */
282
283/*
284 * The control block for an area. This lives in shared memory, at the start of
285 * the first DSM segment controlled by this area.
286 */
287typedef struct
288{
289 /* The segment header for the first segment. */
291 /* The handle for this area. */
293 /* The handles of the segments owned by this area. */
294 dsm_handle segment_handles[DSA_MAX_SEGMENTS];
295 /* Lists of segments, binned by maximum contiguous run of free pages. */
297 /* The object pools for each size class. */
299 /* initial allocation segment size */
301 /* maximum allocation segment size */
303 /* The total size of all active segments. */
305 /* The maximum total size of backing storage we are allowed. */
307 /* Highest used segment index in the history of this area. */
309 /* The reference count for this area. */
311 /* A flag indicating that this area has been pinned. */
312 bool pinned;
313 /* The number of times that segments have been freed. */
315 /* The LWLock tranche ID. */
317 /* The general lock (protects everything except object pools). */
320
321/* Given a pointer to a pool, find a dsa_pointer. */
322#define DsaAreaPoolToDsaPointer(area, p) \
323 DSA_MAKE_POINTER(0, (char *) p - (char *) area->control)
324
325/*
326 * A dsa_segment_map is stored within the backend-private memory of each
327 * individual backend. It holds the base address of the segment within that
328 * backend, plus the addresses of key objects within the segment. Those
329 * could instead be derived from the base address but it's handy to have them
330 * around.
331 */
332typedef struct
333{
334 dsm_segment *segment; /* DSM segment */
335 char *mapped_address; /* Address at which segment is mapped */
336 dsa_segment_header *header; /* Header (same as mapped_address) */
337 FreePageManager *fpm; /* Free page manager within segment. */
338 dsa_pointer *pagemap; /* Page map within segment. */
340
341/*
342 * Per-backend state for a storage area. Backends obtain one of these by
343 * creating an area or attaching to an existing one using a handle. Each
344 * process that needs to use an area uses its own object to track where the
345 * segments are mapped.
346 */
348{
349 /* Pointer to the control object in shared memory. */
351
352 /*
353 * All the mappings are owned by this. The dsa_area itself is not
354 * directly tracked by the ResourceOwner, but the effect is the same. NULL
355 * if the attachment has session lifespan, i.e if dsa_pin_mapping() has
356 * been called.
357 */
359
360 /*
361 * This backend's array of segment maps, ordered by segment index
362 * corresponding to control->segment_handles. Some of the area's segments
363 * may not be mapped in this backend yet, and some slots may have been
364 * freed and need to be detached; these operations happen on demand.
365 */
367
368 /* The highest segment index this backend has ever mapped. */
370
371 /* The last observed freed_segment_counter. */
373};
374
375#define DSA_SPAN_NOTHING_FREE ((uint16) -1)
376#define DSA_SUPERBLOCK_SIZE (DSA_PAGES_PER_SUPERBLOCK * FPM_PAGE_SIZE)
377
378/* Given a pointer to a segment_map, obtain a segment index number. */
379#define get_segment_index(area, segment_map_ptr) \
380 (segment_map_ptr - &area->segment_maps[0])
381
382static void init_span(dsa_area *area, dsa_pointer span_pointer,
383 dsa_area_pool *pool, dsa_pointer start, size_t npages,
384 uint16 size_class);
385static bool transfer_first_span(dsa_area *area, dsa_area_pool *pool,
386 int fromclass, int toclass);
387static inline dsa_pointer alloc_object(dsa_area *area, int size_class);
388static bool ensure_active_superblock(dsa_area *area, dsa_area_pool *pool,
389 int size_class);
392static void destroy_superblock(dsa_area *area, dsa_pointer span_pointer);
393static void unlink_span(dsa_area *area, dsa_area_span *span);
394static void add_span_to_fullness_class(dsa_area *area, dsa_area_span *span,
395 dsa_pointer span_pointer, int fclass);
396static void unlink_segment(dsa_area *area, dsa_segment_map *segment_map);
397static dsa_segment_map *get_best_segment(dsa_area *area, size_t npages);
398static dsa_segment_map *make_new_segment(dsa_area *area, size_t requested_pages);
399static dsa_area *create_internal(void *place, size_t size,
400 int tranche_id,
401 dsm_handle control_handle,
402 dsm_segment *control_segment,
403 size_t init_segment_size,
404 size_t max_segment_size);
405static dsa_area *attach_internal(void *place, dsm_segment *segment,
406 dsa_handle handle);
407static void check_for_freed_segments(dsa_area *area);
409static void rebin_segment(dsa_area *area, dsa_segment_map *segment_map);
410
411/*
412 * Create a new shared area in a new DSM segment. Further DSM segments will
413 * be allocated as required to extend the available space.
414 *
415 * We can't allocate a LWLock tranche_id within this function, because tranche
416 * IDs are a scarce resource; there are only 64k available, using low numbers
417 * when possible matters, and we have no provision for recycling them. So,
418 * we require the caller to provide one.
419 */
420dsa_area *
421dsa_create_ext(int tranche_id, size_t init_segment_size, size_t max_segment_size)
422{
423 dsm_segment *segment;
424 dsa_area *area;
425
426 /*
427 * Create the DSM segment that will hold the shared control object and the
428 * first segment of usable space.
429 */
430 segment = dsm_create(init_segment_size, 0);
431
432 /*
433 * All segments backing this area are pinned, so that DSA can explicitly
434 * control their lifetime (otherwise a newly created segment belonging to
435 * this area might be freed when the only backend that happens to have it
436 * mapped in ends, corrupting the area).
437 */
438 dsm_pin_segment(segment);
439
440 /* Create a new DSA area with the control object in this segment. */
441 area = create_internal(dsm_segment_address(segment),
442 init_segment_size,
443 tranche_id,
444 dsm_segment_handle(segment), segment,
445 init_segment_size, max_segment_size);
446
447 /* Clean up when the control segment detaches. */
450
451 return area;
452}
453
454/*
455 * Create a new shared area in an existing shared memory space, which may be
456 * either DSM or Postmaster-initialized memory. DSM segments will be
457 * allocated as required to extend the available space, though that can be
458 * prevented with dsa_set_size_limit(area, size) using the same size provided
459 * to dsa_create_in_place.
460 *
461 * Areas created in-place must eventually be released by the backend that
462 * created them and all backends that attach to them. This can be done
463 * explicitly with dsa_release_in_place, or, in the special case that 'place'
464 * happens to be in a pre-existing DSM segment, by passing in a pointer to the
465 * segment so that a detach hook can be registered with the containing DSM
466 * segment.
467 *
468 * See dsa_create() for a note about the tranche arguments.
469 */
470dsa_area *
471dsa_create_in_place_ext(void *place, size_t size,
472 int tranche_id, dsm_segment *segment,
473 size_t init_segment_size, size_t max_segment_size)
474{
475 dsa_area *area;
476
477 area = create_internal(place, size, tranche_id,
478 DSM_HANDLE_INVALID, NULL,
479 init_segment_size, max_segment_size);
480
481 /*
482 * Clean up when the control segment detaches, if a containing DSM segment
483 * was provided.
484 */
485 if (segment != NULL)
487 PointerGetDatum(place));
488
489 return area;
490}
491
492/*
493 * Obtain a handle that can be passed to other processes so that they can
494 * attach to the given area. Cannot be called for areas created with
495 * dsa_create_in_place.
496 */
499{
501 return area->control->handle;
502}
503
504/*
505 * Attach to an area given a handle generated (possibly in another process) by
506 * dsa_get_handle. The area must have been created with dsa_create (not
507 * dsa_create_in_place).
508 */
509dsa_area *
511{
512 dsm_segment *segment;
513 dsa_area *area;
514
515 /*
516 * An area handle is really a DSM segment handle for the first segment, so
517 * we go ahead and attach to that.
518 */
519 segment = dsm_attach(handle);
520 if (segment == NULL)
522 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
523 errmsg("could not attach to dynamic shared area")));
524
525 area = attach_internal(dsm_segment_address(segment), segment, handle);
526
527 /* Clean up when the control segment detaches. */
530
531 return area;
532}
533
534/*
535 * Attach to an area that was created with dsa_create_in_place. The caller
536 * must somehow know the location in memory that was used when the area was
537 * created, though it may be mapped at a different virtual address in this
538 * process.
539 *
540 * See dsa_create_in_place for note about releasing in-place areas, and the
541 * optional 'segment' argument which can be provided to allow automatic
542 * release if the containing memory happens to be a DSM segment.
543 */
544dsa_area *
545dsa_attach_in_place(void *place, dsm_segment *segment)
546{
547 dsa_area *area;
548
549 area = attach_internal(place, NULL, DSA_HANDLE_INVALID);
550
551 /*
552 * Clean up when the control segment detaches, if a containing DSM segment
553 * was provided.
554 */
555 if (segment != NULL)
557 PointerGetDatum(place));
558
559 return area;
560}
561
562/*
563 * Release a DSA area that was produced by dsa_create_in_place or
564 * dsa_attach_in_place. The 'segment' argument is ignored but provides an
565 * interface suitable for on_dsm_detach, for the convenience of users who want
566 * to create a DSA segment inside an existing DSM segment and have it
567 * automatically released when the containing DSM segment is detached.
568 * 'place' should be the address of the place where the area was created.
569 *
570 * This callback is automatically registered for the DSM segment containing
571 * the control object of in-place areas when a segment is provided to
572 * dsa_create_in_place or dsa_attach_in_place, and also for all areas created
573 * with dsa_create.
574 */
575void
577{
579}
580
581/*
582 * Release a DSA area that was produced by dsa_create_in_place or
583 * dsa_attach_in_place. The 'code' argument is ignored but provides an
584 * interface suitable for on_shmem_exit or before_shmem_exit, for the
585 * convenience of users who want to create a DSA segment inside shared memory
586 * other than a DSM segment and have it automatically release at backend exit.
587 * 'place' should be the address of the place where the area was created.
588 */
589void
591{
593}
594
595/*
596 * Release a DSA area that was produced by dsa_create_in_place or
597 * dsa_attach_in_place. It is preferable to use one of the 'dsa_on_XXX'
598 * callbacks so that this is managed automatically, because failure to release
599 * an area created in-place leaks its segments permanently.
600 *
601 * This is also called automatically for areas produced by dsa_create or
602 * dsa_attach as an implementation detail.
603 */
604void
606{
607 dsa_area_control *control = (dsa_area_control *) place;
608 int i;
609
610 LWLockAcquire(&control->lock, LW_EXCLUSIVE);
611 Assert(control->segment_header.magic ==
612 (DSA_SEGMENT_HEADER_MAGIC ^ control->handle ^ 0));
613 Assert(control->refcnt > 0);
614 if (--control->refcnt == 0)
615 {
616 for (i = 0; i <= control->high_segment_index; ++i)
617 {
618 dsm_handle handle;
619
620 handle = control->segment_handles[i];
621 if (handle != DSM_HANDLE_INVALID)
622 dsm_unpin_segment(handle);
623 }
624 }
625 LWLockRelease(&control->lock);
626}
627
628/*
629 * Keep a DSA area attached until end of session or explicit detach.
630 *
631 * By default, areas are owned by the current resource owner, which means they
632 * are detached automatically when that scope ends.
633 */
634void
636{
637 int i;
638
639 if (area->resowner != NULL)
640 {
641 area->resowner = NULL;
642
643 for (i = 0; i <= area->high_segment_index; ++i)
644 if (area->segment_maps[i].segment != NULL)
646 }
647}
648
649/*
650 * Allocate memory in this storage area. The return value is a dsa_pointer
651 * that can be passed to other processes, and converted to a local pointer
652 * with dsa_get_address. 'flags' is a bitmap which should be constructed
653 * from the following values:
654 *
655 * DSA_ALLOC_HUGE allows allocations >= 1GB. Otherwise, such allocations
656 * will result in an ERROR.
657 *
658 * DSA_ALLOC_NO_OOM causes this function to return InvalidDsaPointer when
659 * no memory is available or a size limit established by dsa_set_size_limit
660 * would be exceeded. Otherwise, such allocations will result in an ERROR.
661 *
662 * DSA_ALLOC_ZERO causes the allocated memory to be zeroed. Otherwise, the
663 * contents of newly-allocated memory are indeterminate.
664 *
665 * These flags correspond to similarly named flags used by
666 * MemoryContextAllocExtended(). See also the macros dsa_allocate and
667 * dsa_allocate0 which expand to a call to this function with commonly used
668 * flags.
669 */
671dsa_allocate_extended(dsa_area *area, size_t size, int flags)
672{
673 uint16 size_class;
674 dsa_pointer start_pointer;
675 dsa_segment_map *segment_map;
676 dsa_pointer result;
677
678 Assert(size > 0);
679
680 /* Sanity check on huge individual allocation size. */
681 if (((flags & DSA_ALLOC_HUGE) != 0 && !AllocHugeSizeIsValid(size)) ||
682 ((flags & DSA_ALLOC_HUGE) == 0 && !AllocSizeIsValid(size)))
683 elog(ERROR, "invalid DSA memory alloc request size %zu", size);
684
685 /*
686 * If bigger than the largest size class, just grab a run of pages from
687 * the free page manager, instead of allocating an object from a pool.
688 * There will still be a span, but it's a special class of span that
689 * manages this whole allocation and simply gives all pages back to the
690 * free page manager when dsa_free is called.
691 */
693 {
694 size_t npages = fpm_size_to_pages(size);
695 size_t first_page;
696 dsa_pointer span_pointer;
698
699 /* Obtain a span object. */
700 span_pointer = alloc_object(area, DSA_SCLASS_BLOCK_OF_SPANS);
701 if (!DsaPointerIsValid(span_pointer))
702 {
703 /* Raise error unless asked not to. */
704 if ((flags & DSA_ALLOC_NO_OOM) == 0)
706 (errcode(ERRCODE_OUT_OF_MEMORY),
707 errmsg("out of memory"),
708 errdetail("Failed on DSA request of size %zu.",
709 size)));
710 return InvalidDsaPointer;
711 }
712
714
715 /* Find a segment from which to allocate. */
716 segment_map = get_best_segment(area, npages);
717 if (segment_map == NULL)
718 segment_map = make_new_segment(area, npages);
719 if (segment_map == NULL)
720 {
721 /* Can't make any more segments: game over. */
723 dsa_free(area, span_pointer);
724
725 /* Raise error unless asked not to. */
726 if ((flags & DSA_ALLOC_NO_OOM) == 0)
728 (errcode(ERRCODE_OUT_OF_MEMORY),
729 errmsg("out of memory"),
730 errdetail("Failed on DSA request of size %zu.",
731 size)));
732 return InvalidDsaPointer;
733 }
734
735 /*
736 * Ask the free page manager for a run of pages. This should always
737 * succeed, since both get_best_segment and make_new_segment should
738 * only return a non-NULL pointer if it actually contains enough
739 * contiguous freespace. If it does fail, something in our backend
740 * private state is out of whack, so use FATAL to kill the process.
741 */
742 if (!FreePageManagerGet(segment_map->fpm, npages, &first_page))
743 elog(FATAL,
744 "dsa_allocate could not find %zu free pages", npages);
746
747 start_pointer = DSA_MAKE_POINTER(get_segment_index(area, segment_map),
748 first_page * FPM_PAGE_SIZE);
749
750 /* Initialize span and pagemap. */
753 init_span(area, span_pointer, pool, start_pointer, npages,
755 segment_map->pagemap[first_page] = span_pointer;
757
758 /* Zero-initialize the memory if requested. */
759 if ((flags & DSA_ALLOC_ZERO) != 0)
760 memset(dsa_get_address(area, start_pointer), 0, size);
761
762 return start_pointer;
763 }
764
765 /* Map allocation to a size class. */
767 {
768 int mapidx;
769
770 /* For smaller sizes we have a lookup table... */
771 mapidx = ((size + DSA_SIZE_CLASS_MAP_QUANTUM - 1) /
773 size_class = dsa_size_class_map[mapidx];
774 }
775 else
776 {
777 uint16 min;
778 uint16 max;
779
780 /* ... and for the rest we search by binary chop. */
782 max = lengthof(dsa_size_classes) - 1;
783
784 while (min < max)
785 {
786 uint16 mid = (min + max) / 2;
787 uint16 class_size = dsa_size_classes[mid];
788
789 if (class_size < size)
790 min = mid + 1;
791 else
792 max = mid;
793 }
794
795 size_class = min;
796 }
797 Assert(size <= dsa_size_classes[size_class]);
798 Assert(size_class == 0 || size > dsa_size_classes[size_class - 1]);
799
800 /* Attempt to allocate an object from the appropriate pool. */
801 result = alloc_object(area, size_class);
802
803 /* Check for failure to allocate. */
804 if (!DsaPointerIsValid(result))
805 {
806 /* Raise error unless asked not to. */
807 if ((flags & DSA_ALLOC_NO_OOM) == 0)
809 (errcode(ERRCODE_OUT_OF_MEMORY),
810 errmsg("out of memory"),
811 errdetail("Failed on DSA request of size %zu.", size)));
812 return InvalidDsaPointer;
813 }
814
815 /* Zero-initialize the memory if requested. */
816 if ((flags & DSA_ALLOC_ZERO) != 0)
817 memset(dsa_get_address(area, result), 0, size);
818
819 return result;
820}
821
822/*
823 * Free memory obtained with dsa_allocate.
824 */
825void
827{
828 dsa_segment_map *segment_map;
829 int pageno;
830 dsa_pointer span_pointer;
831 dsa_area_span *span;
832 char *superblock;
833 char *object;
834 size_t size;
835 int size_class;
836
837 /* Make sure we don't have a stale segment in the slot 'dp' refers to. */
839
840 /* Locate the object, span and pool. */
841 segment_map = get_segment_by_index(area, DSA_EXTRACT_SEGMENT_NUMBER(dp));
842 pageno = DSA_EXTRACT_OFFSET(dp) / FPM_PAGE_SIZE;
843 span_pointer = segment_map->pagemap[pageno];
844 span = dsa_get_address(area, span_pointer);
845 superblock = dsa_get_address(area, span->start);
846 object = dsa_get_address(area, dp);
847 size_class = span->size_class;
848 size = dsa_size_classes[size_class];
849
850 /*
851 * Special case for large objects that live in a special span: we return
852 * those pages directly to the free page manager and free the span.
853 */
855 {
856
857#ifdef CLOBBER_FREED_MEMORY
858 memset(object, 0x7f, span->npages * FPM_PAGE_SIZE);
859#endif
860
861 /* Give pages back to free page manager. */
863 FreePageManagerPut(segment_map->fpm,
865 span->npages);
866
867 /* Move segment to appropriate bin if necessary. */
868 rebin_segment(area, segment_map);
870
871 /* Unlink span. */
874 unlink_span(area, span);
876 /* Free the span object so it can be reused. */
877 dsa_free(area, span_pointer);
878 return;
879 }
880
881#ifdef CLOBBER_FREED_MEMORY
882 memset(object, 0x7f, size);
883#endif
884
885 LWLockAcquire(DSA_SCLASS_LOCK(area, size_class), LW_EXCLUSIVE);
886
887 /* Put the object on the span's freelist. */
888 Assert(object >= superblock);
889 Assert(object < superblock + DSA_SUPERBLOCK_SIZE);
890 Assert((object - superblock) % size == 0);
891 NextFreeObjectIndex(object) = span->firstfree;
892 span->firstfree = (object - superblock) / size;
893 ++span->nallocatable;
894
895 /*
896 * See if the span needs to moved to a different fullness class, or be
897 * freed so its pages can be given back to the segment.
898 */
899 if (span->nallocatable == 1 && span->fclass == DSA_FULLNESS_CLASSES - 1)
900 {
901 /*
902 * The block was completely full and is located in the
903 * highest-numbered fullness class, which is never scanned for free
904 * chunks. We must move it to the next-lower fullness class.
905 */
906 unlink_span(area, span);
907 add_span_to_fullness_class(area, span, span_pointer,
909
910 /*
911 * If this is the only span, and there is no active span, then we
912 * should probably move this span to fullness class 1. (Otherwise if
913 * you allocate exactly all the objects in the only span, it moves to
914 * class 3, then you free them all, it moves to 2, and then is given
915 * back, leaving no active span).
916 */
917 }
918 else if (span->nallocatable == span->nmax &&
919 (span->fclass != 1 || span->prevspan != InvalidDsaPointer))
920 {
921 /*
922 * This entire block is free, and it's not the active block for this
923 * size class. Return the memory to the free page manager. We don't
924 * do this for the active block to prevent hysteresis: if we
925 * repeatedly allocate and free the only chunk in the active block, it
926 * will be very inefficient if we deallocate and reallocate the block
927 * every time.
928 */
929 destroy_superblock(area, span_pointer);
930 }
931
932 LWLockRelease(DSA_SCLASS_LOCK(area, size_class));
933}
934
935/*
936 * Obtain a backend-local address for a dsa_pointer. 'dp' must point to
937 * memory allocated by the given area (possibly in another process) that
938 * hasn't yet been freed. This may cause a segment to be mapped into the
939 * current process if required, and may cause freed segments to be unmapped.
940 */
941void *
943{
945 size_t offset;
946
947 /* Convert InvalidDsaPointer to NULL. */
948 if (!DsaPointerIsValid(dp))
949 return NULL;
950
951 /* Process any requests to detach from freed segments. */
953
954 /* Break the dsa_pointer into its components. */
956 offset = DSA_EXTRACT_OFFSET(dp);
958
959 /* Check if we need to cause this segment to be mapped in. */
960 if (unlikely(area->segment_maps[index].mapped_address == NULL))
961 {
962 /* Call for effect (we don't need the result). */
964 }
965
966 return area->segment_maps[index].mapped_address + offset;
967}
968
969/*
970 * Pin this area, so that it will continue to exist even if all backends
971 * detach from it. In that case, the area can still be reattached to if a
972 * handle has been recorded somewhere.
973 */
974void
976{
978 if (area->control->pinned)
979 {
981 elog(ERROR, "dsa_area already pinned");
982 }
983 area->control->pinned = true;
984 ++area->control->refcnt;
986}
987
988/*
989 * Undo the effects of dsa_pin, so that the given area can be freed when no
990 * backends are attached to it. May be called only if dsa_pin has been
991 * called.
992 */
993void
995{
997 Assert(area->control->refcnt > 1);
998 if (!area->control->pinned)
999 {
1001 elog(ERROR, "dsa_area not pinned");
1002 }
1003 area->control->pinned = false;
1004 --area->control->refcnt;
1006}
1007
1008/*
1009 * Set the total size limit for this area. This limit is checked whenever new
1010 * segments need to be allocated from the operating system. If the new size
1011 * limit is already exceeded, this has no immediate effect.
1012 *
1013 * Note that the total virtual memory usage may be temporarily larger than
1014 * this limit when segments have been freed, but not yet detached by all
1015 * backends that have attached to them.
1016 */
1017void
1018dsa_set_size_limit(dsa_area *area, size_t limit)
1019{
1021 area->control->max_total_segment_size = limit;
1023}
1024
1025/* Return the total size of all active segments */
1026size_t
1028{
1029 size_t size;
1030
1034
1035 return size;
1036}
1037
1038/*
1039 * Aggressively free all spare memory in the hope of returning DSM segments to
1040 * the operating system.
1041 */
1042void
1044{
1045 int size_class;
1046
1047 /*
1048 * Trim in reverse pool order so we get to the spans-of-spans last, just
1049 * in case any become entirely free while processing all the other pools.
1050 */
1051 for (size_class = DSA_NUM_SIZE_CLASSES - 1; size_class >= 0; --size_class)
1052 {
1053 dsa_area_pool *pool = &area->control->pools[size_class];
1054 dsa_pointer span_pointer;
1055
1056 if (size_class == DSA_SCLASS_SPAN_LARGE)
1057 {
1058 /* Large object frees give back segments aggressively already. */
1059 continue;
1060 }
1061
1062 /*
1063 * Search fullness class 1 only. That is where we expect to find an
1064 * entirely empty superblock (entirely empty superblocks in other
1065 * fullness classes are returned to the free page map by dsa_free).
1066 */
1067 LWLockAcquire(DSA_SCLASS_LOCK(area, size_class), LW_EXCLUSIVE);
1068 span_pointer = pool->spans[1];
1069 while (DsaPointerIsValid(span_pointer))
1070 {
1071 dsa_area_span *span = dsa_get_address(area, span_pointer);
1072 dsa_pointer next = span->nextspan;
1073
1074 if (span->nallocatable == span->nmax)
1075 destroy_superblock(area, span_pointer);
1076
1077 span_pointer = next;
1078 }
1079 LWLockRelease(DSA_SCLASS_LOCK(area, size_class));
1080 }
1081}
1082
1083/*
1084 * Print out debugging information about the internal state of the shared
1085 * memory area.
1086 */
1087void
1089{
1090 size_t i,
1091 j;
1092
1093 /*
1094 * Note: This gives an inconsistent snapshot as it acquires and releases
1095 * individual locks as it goes...
1096 */
1097
1100 fprintf(stderr, "dsa_area handle %x:\n", area->control->handle);
1101 fprintf(stderr, " max_total_segment_size: %zu\n",
1103 fprintf(stderr, " total_segment_size: %zu\n",
1105 fprintf(stderr, " refcnt: %d\n", area->control->refcnt);
1106 fprintf(stderr, " pinned: %c\n", area->control->pinned ? 't' : 'f');
1107 fprintf(stderr, " segment bins:\n");
1108 for (i = 0; i < DSA_NUM_SEGMENT_BINS; ++i)
1109 {
1111 {
1112 dsa_segment_index segment_index;
1113
1114 if (i == 0)
1115 fprintf(stderr,
1116 " segment bin %zu (no contiguous free pages):\n", i);
1117 else
1118 fprintf(stderr,
1119 " segment bin %zu (at least %d contiguous pages free):\n",
1120 i, 1 << (i - 1));
1121 segment_index = area->control->segment_bins[i];
1122 while (segment_index != DSA_SEGMENT_INDEX_NONE)
1123 {
1124 dsa_segment_map *segment_map;
1125
1126 segment_map =
1127 get_segment_by_index(area, segment_index);
1128
1129 fprintf(stderr,
1130 " segment index %zu, usable_pages = %zu, "
1131 "contiguous_pages = %zu, mapped at %p\n",
1132 segment_index,
1133 segment_map->header->usable_pages,
1134 fpm_largest(segment_map->fpm),
1135 segment_map->mapped_address);
1136 segment_index = segment_map->header->next;
1137 }
1138 }
1139 }
1141
1142 fprintf(stderr, " pools:\n");
1143 for (i = 0; i < DSA_NUM_SIZE_CLASSES; ++i)
1144 {
1145 bool found = false;
1146
1148 for (j = 0; j < DSA_FULLNESS_CLASSES; ++j)
1149 if (DsaPointerIsValid(area->control->pools[i].spans[j]))
1150 found = true;
1151 if (found)
1152 {
1154 fprintf(stderr, " pool for blocks of span objects:\n");
1155 else if (i == DSA_SCLASS_SPAN_LARGE)
1156 fprintf(stderr, " pool for large object spans:\n");
1157 else
1158 fprintf(stderr,
1159 " pool for size class %zu (object size %hu bytes):\n",
1160 i, dsa_size_classes[i]);
1161 for (j = 0; j < DSA_FULLNESS_CLASSES; ++j)
1162 {
1163 if (!DsaPointerIsValid(area->control->pools[i].spans[j]))
1164 fprintf(stderr, " fullness class %zu is empty\n", j);
1165 else
1166 {
1167 dsa_pointer span_pointer = area->control->pools[i].spans[j];
1168
1169 fprintf(stderr, " fullness class %zu:\n", j);
1170 while (DsaPointerIsValid(span_pointer))
1171 {
1172 dsa_area_span *span;
1173
1174 span = dsa_get_address(area, span_pointer);
1175 fprintf(stderr,
1176 " span descriptor at "
1177 DSA_POINTER_FORMAT ", superblock at "
1179 ", pages = %zu, objects free = %hu/%hu\n",
1180 span_pointer, span->start, span->npages,
1181 span->nallocatable, span->nmax);
1182 span_pointer = span->nextspan;
1183 }
1184 }
1185 }
1186 }
1188 }
1189}
1190
1191/*
1192 * Return the smallest size that you can successfully provide to
1193 * dsa_create_in_place.
1194 */
1195size_t
1197{
1198 size_t size;
1199 int pages = 0;
1200
1201 size = MAXALIGN(sizeof(dsa_area_control)) +
1202 MAXALIGN(sizeof(FreePageManager));
1203
1204 /* Figure out how many pages we need, including the page map... */
1205 while (((size + FPM_PAGE_SIZE - 1) / FPM_PAGE_SIZE) > pages)
1206 {
1207 ++pages;
1208 size += sizeof(dsa_pointer);
1209 }
1210
1211 return pages * FPM_PAGE_SIZE;
1212}
1213
1214/*
1215 * Workhorse function for dsa_create and dsa_create_in_place.
1216 */
1217static dsa_area *
1218create_internal(void *place, size_t size,
1219 int tranche_id,
1220 dsm_handle control_handle,
1221 dsm_segment *control_segment,
1222 size_t init_segment_size, size_t max_segment_size)
1223{
1224 dsa_area_control *control;
1225 dsa_area *area;
1226 dsa_segment_map *segment_map;
1227 size_t usable_pages;
1228 size_t total_pages;
1229 size_t metadata_bytes;
1230 int i;
1231
1232 /* Check the initial and maximum block sizes */
1233 Assert(init_segment_size >= DSA_MIN_SEGMENT_SIZE);
1234 Assert(max_segment_size >= init_segment_size);
1235 Assert(max_segment_size <= DSA_MAX_SEGMENT_SIZE);
1236
1237 /* Sanity check on the space we have to work in. */
1238 if (size < dsa_minimum_size())
1239 elog(ERROR, "dsa_area space must be at least %zu, but %zu provided",
1241
1242 /* Now figure out how much space is usable */
1243 total_pages = size / FPM_PAGE_SIZE;
1244 metadata_bytes =
1245 MAXALIGN(sizeof(dsa_area_control)) +
1246 MAXALIGN(sizeof(FreePageManager)) +
1247 total_pages * sizeof(dsa_pointer);
1248 /* Add padding up to next page boundary. */
1249 if (metadata_bytes % FPM_PAGE_SIZE != 0)
1250 metadata_bytes += FPM_PAGE_SIZE - (metadata_bytes % FPM_PAGE_SIZE);
1251 Assert(metadata_bytes <= size);
1252 usable_pages = (size - metadata_bytes) / FPM_PAGE_SIZE;
1253
1254 /*
1255 * Initialize the dsa_area_control object located at the start of the
1256 * space.
1257 */
1258 control = (dsa_area_control *) place;
1259 memset(place, 0, sizeof(*control));
1260 control->segment_header.magic =
1261 DSA_SEGMENT_HEADER_MAGIC ^ control_handle ^ 0;
1264 control->segment_header.usable_pages = usable_pages;
1265 control->segment_header.freed = false;
1266 control->segment_header.size = size;
1267 control->handle = control_handle;
1268 control->init_segment_size = init_segment_size;
1269 control->max_segment_size = max_segment_size;
1270 control->max_total_segment_size = (size_t) -1;
1271 control->total_segment_size = size;
1272 control->segment_handles[0] = control_handle;
1273 for (i = 0; i < DSA_NUM_SEGMENT_BINS; ++i)
1275 control->refcnt = 1;
1276 control->lwlock_tranche_id = tranche_id;
1277
1278 /*
1279 * Create the dsa_area object that this backend will use to access the
1280 * area. Other backends will need to obtain their own dsa_area object by
1281 * attaching.
1282 */
1283 area = palloc(sizeof(dsa_area));
1284 area->control = control;
1286 memset(area->segment_maps, 0, sizeof(dsa_segment_map) * DSA_MAX_SEGMENTS);
1287 area->high_segment_index = 0;
1288 area->freed_segment_counter = 0;
1289 LWLockInitialize(&control->lock, control->lwlock_tranche_id);
1290 for (i = 0; i < DSA_NUM_SIZE_CLASSES; ++i)
1292 control->lwlock_tranche_id);
1293
1294 /* Set up the segment map for this process's mapping. */
1295 segment_map = &area->segment_maps[0];
1296 segment_map->segment = control_segment;
1297 segment_map->mapped_address = place;
1298 segment_map->header = (dsa_segment_header *) place;
1299 segment_map->fpm = (FreePageManager *)
1300 (segment_map->mapped_address +
1301 MAXALIGN(sizeof(dsa_area_control)));
1302 segment_map->pagemap = (dsa_pointer *)
1303 (segment_map->mapped_address +
1304 MAXALIGN(sizeof(dsa_area_control)) +
1305 MAXALIGN(sizeof(FreePageManager)));
1306
1307 /* Set up the free page map. */
1308 FreePageManagerInitialize(segment_map->fpm, segment_map->mapped_address);
1309 /* There can be 0 usable pages if size is dsa_minimum_size(). */
1310
1311 if (usable_pages > 0)
1312 FreePageManagerPut(segment_map->fpm, metadata_bytes / FPM_PAGE_SIZE,
1313 usable_pages);
1314
1315 /* Put this segment into the appropriate bin. */
1316 control->segment_bins[contiguous_pages_to_segment_bin(usable_pages)] = 0;
1317 segment_map->header->bin = contiguous_pages_to_segment_bin(usable_pages);
1318
1319 return area;
1320}
1321
1322/*
1323 * Workhorse function for dsa_attach and dsa_attach_in_place.
1324 */
1325static dsa_area *
1326attach_internal(void *place, dsm_segment *segment, dsa_handle handle)
1327{
1328 dsa_area_control *control;
1329 dsa_area *area;
1330 dsa_segment_map *segment_map;
1331
1332 control = (dsa_area_control *) place;
1333 Assert(control->handle == handle);
1334 Assert(control->segment_handles[0] == handle);
1335 Assert(control->segment_header.magic ==
1336 (DSA_SEGMENT_HEADER_MAGIC ^ handle ^ 0));
1337
1338 /* Build the backend-local area object. */
1339 area = palloc(sizeof(dsa_area));
1340 area->control = control;
1342 memset(&area->segment_maps[0], 0,
1344 area->high_segment_index = 0;
1345
1346 /* Set up the segment map for this process's mapping. */
1347 segment_map = &area->segment_maps[0];
1348 segment_map->segment = segment; /* NULL for in-place */
1349 segment_map->mapped_address = place;
1350 segment_map->header = (dsa_segment_header *) segment_map->mapped_address;
1351 segment_map->fpm = (FreePageManager *)
1352 (segment_map->mapped_address + MAXALIGN(sizeof(dsa_area_control)));
1353 segment_map->pagemap = (dsa_pointer *)
1354 (segment_map->mapped_address + MAXALIGN(sizeof(dsa_area_control)) +
1355 MAXALIGN(sizeof(FreePageManager)));
1356
1357 /* Bump the reference count. */
1359 if (control->refcnt == 0)
1360 {
1361 /* We can't attach to a DSA area that has already been destroyed. */
1362 ereport(ERROR,
1363 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1364 errmsg("could not attach to dynamic shared area")));
1365 }
1366 ++control->refcnt;
1369
1370 return area;
1371}
1372
1373/*
1374 * Add a new span to fullness class 1 of the indicated pool.
1375 */
1376static void
1378 dsa_pointer span_pointer,
1379 dsa_area_pool *pool, dsa_pointer start, size_t npages,
1380 uint16 size_class)
1381{
1382 dsa_area_span *span = dsa_get_address(area, span_pointer);
1383 size_t obsize = dsa_size_classes[size_class];
1384
1385 /*
1386 * The per-pool lock must be held because we manipulate the span list for
1387 * this pool.
1388 */
1389 Assert(LWLockHeldByMe(DSA_SCLASS_LOCK(area, size_class)));
1390
1391 /* Push this span onto the front of the span list for fullness class 1. */
1392 if (DsaPointerIsValid(pool->spans[1]))
1393 {
1394 dsa_area_span *head = (dsa_area_span *)
1395 dsa_get_address(area, pool->spans[1]);
1396
1397 head->prevspan = span_pointer;
1398 }
1399 span->pool = DsaAreaPoolToDsaPointer(area, pool);
1400 span->nextspan = pool->spans[1];
1402 pool->spans[1] = span_pointer;
1403
1404 span->start = start;
1405 span->npages = npages;
1406 span->size_class = size_class;
1407 span->ninitialized = 0;
1408 if (size_class == DSA_SCLASS_BLOCK_OF_SPANS)
1409 {
1410 /*
1411 * A block-of-spans contains its own descriptor, so mark one object as
1412 * initialized and reduce the count of allocatable objects by one.
1413 * Doing this here has the side effect of also reducing nmax by one,
1414 * which is important to make sure we free this object at the correct
1415 * time.
1416 */
1417 span->ninitialized = 1;
1418 span->nallocatable = FPM_PAGE_SIZE / obsize - 1;
1419 }
1420 else if (size_class != DSA_SCLASS_SPAN_LARGE)
1421 span->nallocatable = DSA_SUPERBLOCK_SIZE / obsize;
1423 span->nmax = span->nallocatable;
1424 span->fclass = 1;
1425}
1426
1427/*
1428 * Transfer the first span in one fullness class to the head of another
1429 * fullness class.
1430 */
1431static bool
1433 dsa_area_pool *pool, int fromclass, int toclass)
1434{
1435 dsa_pointer span_pointer;
1436 dsa_area_span *span;
1437 dsa_area_span *nextspan;
1438
1439 /* Can't do it if source list is empty. */
1440 span_pointer = pool->spans[fromclass];
1441 if (!DsaPointerIsValid(span_pointer))
1442 return false;
1443
1444 /* Remove span from head of source list. */
1445 span = dsa_get_address(area, span_pointer);
1446 pool->spans[fromclass] = span->nextspan;
1447 if (DsaPointerIsValid(span->nextspan))
1448 {
1449 nextspan = (dsa_area_span *)
1450 dsa_get_address(area, span->nextspan);
1451 nextspan->prevspan = InvalidDsaPointer;
1452 }
1453
1454 /* Add span to head of target list. */
1455 span->nextspan = pool->spans[toclass];
1456 pool->spans[toclass] = span_pointer;
1457 if (DsaPointerIsValid(span->nextspan))
1458 {
1459 nextspan = (dsa_area_span *)
1460 dsa_get_address(area, span->nextspan);
1461 nextspan->prevspan = span_pointer;
1462 }
1463 span->fclass = toclass;
1464
1465 return true;
1466}
1467
1468/*
1469 * Allocate one object of the requested size class from the given area.
1470 */
1471static inline dsa_pointer
1472alloc_object(dsa_area *area, int size_class)
1473{
1474 dsa_area_pool *pool = &area->control->pools[size_class];
1475 dsa_area_span *span;
1476 dsa_pointer block;
1477 dsa_pointer result;
1478 char *object;
1479 size_t size;
1480
1481 /*
1482 * Even though ensure_active_superblock can in turn call alloc_object if
1483 * it needs to allocate a new span, that's always from a different pool,
1484 * and the order of lock acquisition is always the same, so it's OK that
1485 * we hold this lock for the duration of this function.
1486 */
1487 Assert(!LWLockHeldByMe(DSA_SCLASS_LOCK(area, size_class)));
1488 LWLockAcquire(DSA_SCLASS_LOCK(area, size_class), LW_EXCLUSIVE);
1489
1490 /*
1491 * If there's no active superblock, we must successfully obtain one or
1492 * fail the request.
1493 */
1494 if (!DsaPointerIsValid(pool->spans[1]) &&
1495 !ensure_active_superblock(area, pool, size_class))
1496 {
1497 result = InvalidDsaPointer;
1498 }
1499 else
1500 {
1501 /*
1502 * There should be a block in fullness class 1 at this point, and it
1503 * should never be completely full. Thus we can either pop an object
1504 * from the free list or, failing that, initialize a new object.
1505 */
1506 Assert(DsaPointerIsValid(pool->spans[1]));
1507 span = (dsa_area_span *)
1508 dsa_get_address(area, pool->spans[1]);
1509 Assert(span->nallocatable > 0);
1510 block = span->start;
1511 Assert(size_class < DSA_NUM_SIZE_CLASSES);
1512 size = dsa_size_classes[size_class];
1513 if (span->firstfree != DSA_SPAN_NOTHING_FREE)
1514 {
1515 result = block + span->firstfree * size;
1516 object = dsa_get_address(area, result);
1517 span->firstfree = NextFreeObjectIndex(object);
1518 }
1519 else
1520 {
1521 result = block + span->ninitialized * size;
1522 ++span->ninitialized;
1523 }
1524 --span->nallocatable;
1525
1526 /* If it's now full, move it to the highest-numbered fullness class. */
1527 if (span->nallocatable == 0)
1528 transfer_first_span(area, pool, 1, DSA_FULLNESS_CLASSES - 1);
1529 }
1530
1531 Assert(LWLockHeldByMe(DSA_SCLASS_LOCK(area, size_class)));
1532 LWLockRelease(DSA_SCLASS_LOCK(area, size_class));
1533
1534 return result;
1535}
1536
1537/*
1538 * Ensure an active (i.e. fullness class 1) superblock, unless all existing
1539 * superblocks are completely full and no more can be allocated.
1540 *
1541 * Fullness classes K of 0..N are loosely intended to represent blocks whose
1542 * utilization percentage is at least K/N, but we only enforce this rigorously
1543 * for the highest-numbered fullness class, which always contains exactly
1544 * those blocks that are completely full. It's otherwise acceptable for a
1545 * block to be in a higher-numbered fullness class than the one to which it
1546 * logically belongs. In addition, the active block, which is always the
1547 * first block in fullness class 1, is permitted to have a higher allocation
1548 * percentage than would normally be allowable for that fullness class; we
1549 * don't move it until it's completely full, and then it goes to the
1550 * highest-numbered fullness class.
1551 *
1552 * It might seem odd that the active block is the head of fullness class 1
1553 * rather than fullness class 0, but experience with other allocators has
1554 * shown that it's usually better to allocate from a block that's moderately
1555 * full rather than one that's nearly empty. Insofar as is reasonably
1556 * possible, we want to avoid performing new allocations in a block that would
1557 * otherwise become empty soon.
1558 */
1559static bool
1561 int size_class)
1562{
1563 dsa_pointer span_pointer;
1564 dsa_pointer start_pointer;
1565 size_t obsize = dsa_size_classes[size_class];
1566 size_t nmax;
1567 int fclass;
1568 size_t npages = 1;
1569 size_t first_page;
1570 size_t i;
1571 dsa_segment_map *segment_map;
1572
1573 Assert(LWLockHeldByMe(DSA_SCLASS_LOCK(area, size_class)));
1574
1575 /*
1576 * Compute the number of objects that will fit in a block of this size
1577 * class. Span-of-spans blocks are just a single page, and the first
1578 * object isn't available for use because it describes the block-of-spans
1579 * itself.
1580 */
1581 if (size_class == DSA_SCLASS_BLOCK_OF_SPANS)
1582 nmax = FPM_PAGE_SIZE / obsize - 1;
1583 else
1584 nmax = DSA_SUPERBLOCK_SIZE / obsize;
1585
1586 /*
1587 * If fullness class 1 is empty, try to find a span to put in it by
1588 * scanning higher-numbered fullness classes (excluding the last one,
1589 * whose blocks are certain to all be completely full).
1590 */
1591 for (fclass = 2; fclass < DSA_FULLNESS_CLASSES - 1; ++fclass)
1592 {
1593 span_pointer = pool->spans[fclass];
1594
1595 while (DsaPointerIsValid(span_pointer))
1596 {
1597 int tfclass;
1598 dsa_area_span *span;
1599 dsa_area_span *nextspan;
1600 dsa_area_span *prevspan;
1601 dsa_pointer next_span_pointer;
1602
1603 span = (dsa_area_span *)
1604 dsa_get_address(area, span_pointer);
1605 next_span_pointer = span->nextspan;
1606
1607 /* Figure out what fullness class should contain this span. */
1608 tfclass = (nmax - span->nallocatable)
1609 * (DSA_FULLNESS_CLASSES - 1) / nmax;
1610
1611 /* Look up next span. */
1612 if (DsaPointerIsValid(span->nextspan))
1613 nextspan = (dsa_area_span *)
1614 dsa_get_address(area, span->nextspan);
1615 else
1616 nextspan = NULL;
1617
1618 /*
1619 * If utilization has dropped enough that this now belongs in some
1620 * other fullness class, move it there.
1621 */
1622 if (tfclass < fclass)
1623 {
1624 /* Remove from the current fullness class list. */
1625 if (pool->spans[fclass] == span_pointer)
1626 {
1627 /* It was the head; remove it. */
1629 pool->spans[fclass] = span->nextspan;
1630 if (nextspan != NULL)
1631 nextspan->prevspan = InvalidDsaPointer;
1632 }
1633 else
1634 {
1635 /* It was not the head. */
1637 prevspan = (dsa_area_span *)
1638 dsa_get_address(area, span->prevspan);
1639 prevspan->nextspan = span->nextspan;
1640 }
1641 if (nextspan != NULL)
1642 nextspan->prevspan = span->prevspan;
1643
1644 /* Push onto the head of the new fullness class list. */
1645 span->nextspan = pool->spans[tfclass];
1646 pool->spans[tfclass] = span_pointer;
1648 if (DsaPointerIsValid(span->nextspan))
1649 {
1650 nextspan = (dsa_area_span *)
1651 dsa_get_address(area, span->nextspan);
1652 nextspan->prevspan = span_pointer;
1653 }
1654 span->fclass = tfclass;
1655 }
1656
1657 /* Advance to next span on list. */
1658 span_pointer = next_span_pointer;
1659 }
1660
1661 /* Stop now if we found a suitable block. */
1662 if (DsaPointerIsValid(pool->spans[1]))
1663 return true;
1664 }
1665
1666 /*
1667 * If there are no blocks that properly belong in fullness class 1, pick
1668 * one from some other fullness class and move it there anyway, so that we
1669 * have an allocation target. Our last choice is to transfer a block
1670 * that's almost empty (and might become completely empty soon if left
1671 * alone), but even that is better than failing, which is what we must do
1672 * if there are no blocks at all with freespace.
1673 */
1674 Assert(!DsaPointerIsValid(pool->spans[1]));
1675 for (fclass = 2; fclass < DSA_FULLNESS_CLASSES - 1; ++fclass)
1676 if (transfer_first_span(area, pool, fclass, 1))
1677 return true;
1678 if (!DsaPointerIsValid(pool->spans[1]) &&
1679 transfer_first_span(area, pool, 0, 1))
1680 return true;
1681
1682 /*
1683 * We failed to find an existing span with free objects, so we need to
1684 * allocate a new superblock and construct a new span to manage it.
1685 *
1686 * First, get a dsa_area_span object to describe the new superblock block
1687 * ... unless this allocation is for a dsa_area_span object, in which case
1688 * that's surely not going to work. We handle that case by storing the
1689 * span describing a block-of-spans inline.
1690 */
1691 if (size_class != DSA_SCLASS_BLOCK_OF_SPANS)
1692 {
1693 span_pointer = alloc_object(area, DSA_SCLASS_BLOCK_OF_SPANS);
1694 if (!DsaPointerIsValid(span_pointer))
1695 return false;
1696 npages = DSA_PAGES_PER_SUPERBLOCK;
1697 }
1698
1699 /* Find or create a segment and allocate the superblock. */
1701 segment_map = get_best_segment(area, npages);
1702 if (segment_map == NULL)
1703 {
1704 segment_map = make_new_segment(area, npages);
1705 if (segment_map == NULL)
1706 {
1708 return false;
1709 }
1710 }
1711
1712 /*
1713 * This shouldn't happen: get_best_segment() or make_new_segment()
1714 * promised that we can successfully allocate npages.
1715 */
1716 if (!FreePageManagerGet(segment_map->fpm, npages, &first_page))
1717 elog(FATAL,
1718 "dsa_allocate could not find %zu free pages for superblock",
1719 npages);
1721
1722 /* Compute the start of the superblock. */
1723 start_pointer =
1724 DSA_MAKE_POINTER(get_segment_index(area, segment_map),
1725 first_page * FPM_PAGE_SIZE);
1726
1727 /*
1728 * If this is a block-of-spans, carve the descriptor right out of the
1729 * allocated space.
1730 */
1731 if (size_class == DSA_SCLASS_BLOCK_OF_SPANS)
1732 {
1733 /*
1734 * We have a pointer into the segment. We need to build a dsa_pointer
1735 * from the segment index and offset into the segment.
1736 */
1737 span_pointer = start_pointer;
1738 }
1739
1740 /* Initialize span and pagemap. */
1741 init_span(area, span_pointer, pool, start_pointer, npages, size_class);
1742 for (i = 0; i < npages; ++i)
1743 segment_map->pagemap[first_page + i] = span_pointer;
1744
1745 return true;
1746}
1747
1748/*
1749 * Return the segment map corresponding to a given segment index, mapping the
1750 * segment in if necessary. For internal segment book-keeping, this is called
1751 * with the area lock held. It is also called by dsa_free and dsa_get_address
1752 * without any locking, relying on the fact they have a known live segment
1753 * index and they always call check_for_freed_segments to ensures that any
1754 * freed segment occupying the same slot is detached first.
1755 */
1756static dsa_segment_map *
1758{
1759 if (unlikely(area->segment_maps[index].mapped_address == NULL))
1760 {
1761 dsm_handle handle;
1762 dsm_segment *segment;
1763 dsa_segment_map *segment_map;
1764 ResourceOwner oldowner;
1765
1766 /*
1767 * If we are reached by dsa_free or dsa_get_address, there must be at
1768 * least one object allocated in the referenced segment. Otherwise,
1769 * their caller has a double-free or access-after-free bug, which we
1770 * have no hope of detecting. So we know it's safe to access this
1771 * array slot without holding a lock; it won't change underneath us.
1772 * Furthermore, we know that we can see the latest contents of the
1773 * slot, as explained in check_for_freed_segments, which those
1774 * functions call before arriving here.
1775 */
1776 handle = area->control->segment_handles[index];
1777
1778 /* It's an error to try to access an unused slot. */
1779 if (handle == DSM_HANDLE_INVALID)
1780 elog(ERROR,
1781 "dsa_area could not attach to a segment that has been freed");
1782
1783 oldowner = CurrentResourceOwner;
1785 segment = dsm_attach(handle);
1786 CurrentResourceOwner = oldowner;
1787 if (segment == NULL)
1788 elog(ERROR, "dsa_area could not attach to segment");
1789 segment_map = &area->segment_maps[index];
1790 segment_map->segment = segment;
1791 segment_map->mapped_address = dsm_segment_address(segment);
1792 segment_map->header =
1793 (dsa_segment_header *) segment_map->mapped_address;
1794 segment_map->fpm = (FreePageManager *)
1795 (segment_map->mapped_address +
1796 MAXALIGN(sizeof(dsa_segment_header)));
1797 segment_map->pagemap = (dsa_pointer *)
1798 (segment_map->mapped_address +
1799 MAXALIGN(sizeof(dsa_segment_header)) +
1800 MAXALIGN(sizeof(FreePageManager)));
1801
1802 /* Remember the highest index this backend has ever mapped. */
1803 if (area->high_segment_index < index)
1804 area->high_segment_index = index;
1805
1806 Assert(segment_map->header->magic ==
1808 }
1809
1810 /*
1811 * Callers of dsa_get_address() and dsa_free() don't hold the area lock,
1812 * but it's a bug in the calling code and undefined behavior if the
1813 * address is not live (ie if the segment might possibly have been freed,
1814 * they're trying to use a dangling pointer).
1815 *
1816 * For dsa.c code that holds the area lock to manipulate segment_bins
1817 * lists, it would be a bug if we ever reach a freed segment here. After
1818 * it's marked as freed, the only thing any backend should do with it is
1819 * unmap it, and it should always have done that in
1820 * check_for_freed_segments_locked() before arriving here to resolve an
1821 * index to a segment_map.
1822 *
1823 * Either way we can assert that we aren't returning a freed segment.
1824 */
1826
1827 return &area->segment_maps[index];
1828}
1829
1830/*
1831 * Return a superblock to the free page manager. If the underlying segment
1832 * has become entirely free, then return it to the operating system.
1833 *
1834 * The appropriate pool lock must be held.
1835 */
1836static void
1838{
1839 dsa_area_span *span = dsa_get_address(area, span_pointer);
1840 int size_class = span->size_class;
1841 dsa_segment_map *segment_map;
1842
1843
1844 /* Remove it from its fullness class list. */
1845 unlink_span(area, span);
1846
1847 /*
1848 * Note: Here we acquire the area lock while we already hold a per-pool
1849 * lock. We never hold the area lock and then take a pool lock, or we
1850 * could deadlock.
1851 */
1854 segment_map =
1856 FreePageManagerPut(segment_map->fpm,
1858 span->npages);
1859 /* Check if the segment is now entirely free. */
1860 if (fpm_largest(segment_map->fpm) == segment_map->header->usable_pages)
1861 {
1862 dsa_segment_index index = get_segment_index(area, segment_map);
1863
1864 /* If it's not the segment with extra control data, free it. */
1865 if (index != 0)
1866 {
1867 /*
1868 * Give it back to the OS, and allow other backends to detect that
1869 * they need to detach.
1870 */
1871 unlink_segment(area, segment_map);
1872 segment_map->header->freed = true;
1874 segment_map->header->size);
1875 area->control->total_segment_size -=
1876 segment_map->header->size;
1878 dsm_detach(segment_map->segment);
1881 segment_map->segment = NULL;
1882 segment_map->header = NULL;
1883 segment_map->mapped_address = NULL;
1884 }
1885 }
1886
1887 /* Move segment to appropriate bin if necessary. */
1888 if (segment_map->header != NULL)
1889 rebin_segment(area, segment_map);
1890
1892
1893 /*
1894 * Span-of-spans blocks store the span which describes them within the
1895 * block itself, so freeing the storage implicitly frees the descriptor
1896 * also. If this is a block of any other type, we need to separately free
1897 * the span object also. This recursive call to dsa_free will acquire the
1898 * span pool's lock. We can't deadlock because the acquisition order is
1899 * always some other pool and then the span pool.
1900 */
1901 if (size_class != DSA_SCLASS_BLOCK_OF_SPANS)
1902 dsa_free(area, span_pointer);
1903}
1904
1905static void
1907{
1908 if (DsaPointerIsValid(span->nextspan))
1909 {
1911
1912 next->prevspan = span->prevspan;
1913 }
1914 if (DsaPointerIsValid(span->prevspan))
1915 {
1916 dsa_area_span *prev = dsa_get_address(area, span->prevspan);
1917
1918 prev->nextspan = span->nextspan;
1919 }
1920 else
1921 {
1922 dsa_area_pool *pool = dsa_get_address(area, span->pool);
1923
1924 pool->spans[span->fclass] = span->nextspan;
1925 }
1926}
1927
1928static void
1930 dsa_pointer span_pointer,
1931 int fclass)
1932{
1933 dsa_area_pool *pool = dsa_get_address(area, span->pool);
1934
1935 if (DsaPointerIsValid(pool->spans[fclass]))
1936 {
1937 dsa_area_span *head = dsa_get_address(area,
1938 pool->spans[fclass]);
1939
1940 head->prevspan = span_pointer;
1941 }
1943 span->nextspan = pool->spans[fclass];
1944 pool->spans[fclass] = span_pointer;
1945 span->fclass = fclass;
1946}
1947
1948/*
1949 * Detach from an area that was either created or attached to by this process.
1950 */
1951void
1953{
1954 int i;
1955
1956 /* Detach from all segments. */
1957 for (i = 0; i <= area->high_segment_index; ++i)
1958 if (area->segment_maps[i].segment != NULL)
1960
1961 /*
1962 * Note that 'detaching' (= detaching from DSM segments) doesn't include
1963 * 'releasing' (= adjusting the reference count). It would be nice to
1964 * combine these operations, but client code might never get around to
1965 * calling dsa_detach because of an error path, and a detach hook on any
1966 * particular segment is too late to detach other segments in the area
1967 * without risking a 'leak' warning in the non-error path.
1968 */
1969
1970 /* Free the backend-local area object. */
1971 pfree(area);
1972}
1973
1974/*
1975 * Unlink a segment from the bin that contains it.
1976 */
1977static void
1979{
1980 if (segment_map->header->prev != DSA_SEGMENT_INDEX_NONE)
1981 {
1982 dsa_segment_map *prev;
1983
1984 prev = get_segment_by_index(area, segment_map->header->prev);
1985 prev->header->next = segment_map->header->next;
1986 }
1987 else
1988 {
1989 Assert(area->control->segment_bins[segment_map->header->bin] ==
1990 get_segment_index(area, segment_map));
1991 area->control->segment_bins[segment_map->header->bin] =
1992 segment_map->header->next;
1993 }
1994 if (segment_map->header->next != DSA_SEGMENT_INDEX_NONE)
1995 {
1997
1998 next = get_segment_by_index(area, segment_map->header->next);
1999 next->header->prev = segment_map->header->prev;
2000 }
2001}
2002
2003/*
2004 * Find a segment that could satisfy a request for 'npages' of contiguous
2005 * memory, or return NULL if none can be found. This may involve attaching to
2006 * segments that weren't previously attached so that we can query their free
2007 * pages map.
2008 */
2009static dsa_segment_map *
2010get_best_segment(dsa_area *area, size_t npages)
2011{
2012 size_t bin;
2013
2016
2017 /*
2018 * Start searching from the first bin that *might* have enough contiguous
2019 * pages.
2020 */
2021 for (bin = contiguous_pages_to_segment_bin(npages);
2023 ++bin)
2024 {
2025 /*
2026 * The minimum contiguous size that any segment in this bin should
2027 * have. We'll re-bin if we see segments with fewer.
2028 */
2029 size_t threshold = (size_t) 1 << (bin - 1);
2030 dsa_segment_index segment_index;
2031
2032 /* Search this bin for a segment with enough contiguous space. */
2033 segment_index = area->control->segment_bins[bin];
2034 while (segment_index != DSA_SEGMENT_INDEX_NONE)
2035 {
2036 dsa_segment_map *segment_map;
2037 dsa_segment_index next_segment_index;
2038 size_t contiguous_pages;
2039
2040 segment_map = get_segment_by_index(area, segment_index);
2041 next_segment_index = segment_map->header->next;
2042 contiguous_pages = fpm_largest(segment_map->fpm);
2043
2044 /* Not enough for the request, still enough for this bin. */
2045 if (contiguous_pages >= threshold && contiguous_pages < npages)
2046 {
2047 segment_index = next_segment_index;
2048 continue;
2049 }
2050
2051 /* Re-bin it if it's no longer in the appropriate bin. */
2052 if (contiguous_pages < threshold)
2053 {
2054 rebin_segment(area, segment_map);
2055
2056 /*
2057 * But fall through to see if it's enough to satisfy this
2058 * request anyway....
2059 */
2060 }
2061
2062 /* Check if we are done. */
2063 if (contiguous_pages >= npages)
2064 return segment_map;
2065
2066 /* Continue searching the same bin. */
2067 segment_index = next_segment_index;
2068 }
2069 }
2070
2071 /* Not found. */
2072 return NULL;
2073}
2074
2075/*
2076 * Create a new segment that can handle at least requested_pages. Returns
2077 * NULL if the requested total size limit or maximum allowed number of
2078 * segments would be exceeded.
2079 */
2080static dsa_segment_map *
2081make_new_segment(dsa_area *area, size_t requested_pages)
2082{
2083 dsa_segment_index new_index;
2084 size_t metadata_bytes;
2085 size_t total_size;
2086 size_t total_pages;
2087 size_t usable_pages;
2088 dsa_segment_map *segment_map;
2089 dsm_segment *segment;
2090 ResourceOwner oldowner;
2091
2093
2094 /* Find a segment slot that is not in use (linearly for now). */
2095 for (new_index = 1; new_index < DSA_MAX_SEGMENTS; ++new_index)
2096 {
2097 if (area->control->segment_handles[new_index] == DSM_HANDLE_INVALID)
2098 break;
2099 }
2100 if (new_index == DSA_MAX_SEGMENTS)
2101 return NULL;
2102
2103 /*
2104 * If the total size limit is already exceeded, then we exit early and
2105 * avoid arithmetic wraparound in the unsigned expressions below.
2106 */
2107 if (area->control->total_segment_size >=
2109 return NULL;
2110
2111 /*
2112 * The size should be at least as big as requested, and at least big
2113 * enough to follow a geometric series that approximately doubles the
2114 * total storage each time we create a new segment. We use geometric
2115 * growth because the underlying DSM system isn't designed for large
2116 * numbers of segments (otherwise we might even consider just using one
2117 * DSM segment for each large allocation and for each superblock, and then
2118 * we wouldn't need to use FreePageManager).
2119 *
2120 * We decide on a total segment size first, so that we produce tidy
2121 * power-of-two sized segments. This is a good property to have if we
2122 * move to huge pages in the future. Then we work back to the number of
2123 * pages we can fit.
2124 */
2126 ((size_t) 1 << (new_index / DSA_NUM_SEGMENTS_AT_EACH_SIZE));
2131
2132 total_pages = total_size / FPM_PAGE_SIZE;
2133 metadata_bytes =
2134 MAXALIGN(sizeof(dsa_segment_header)) +
2135 MAXALIGN(sizeof(FreePageManager)) +
2136 sizeof(dsa_pointer) * total_pages;
2137
2138 /* Add padding up to next page boundary. */
2139 if (metadata_bytes % FPM_PAGE_SIZE != 0)
2140 metadata_bytes += FPM_PAGE_SIZE - (metadata_bytes % FPM_PAGE_SIZE);
2141 if (total_size <= metadata_bytes)
2142 return NULL;
2143 usable_pages = (total_size - metadata_bytes) / FPM_PAGE_SIZE;
2144 Assert(metadata_bytes + usable_pages * FPM_PAGE_SIZE <= total_size);
2145
2146 /* See if that is enough... */
2147 if (requested_pages > usable_pages)
2148 {
2149 /*
2150 * We'll make an odd-sized segment, working forward from the requested
2151 * number of pages.
2152 */
2153 usable_pages = requested_pages;
2154 metadata_bytes =
2155 MAXALIGN(sizeof(dsa_segment_header)) +
2156 MAXALIGN(sizeof(FreePageManager)) +
2157 usable_pages * sizeof(dsa_pointer);
2158
2159 /* Add padding up to next page boundary. */
2160 if (metadata_bytes % FPM_PAGE_SIZE != 0)
2161 metadata_bytes += FPM_PAGE_SIZE - (metadata_bytes % FPM_PAGE_SIZE);
2162 total_size = metadata_bytes + usable_pages * FPM_PAGE_SIZE;
2163
2164 /* Is that too large for dsa_pointer's addressing scheme? */
2166 return NULL;
2167
2168 /* Would that exceed the limit? */
2171 return NULL;
2172 }
2173
2174 /* Create the segment. */
2175 oldowner = CurrentResourceOwner;
2177 segment = dsm_create(total_size, 0);
2178 CurrentResourceOwner = oldowner;
2179 if (segment == NULL)
2180 return NULL;
2181 dsm_pin_segment(segment);
2182
2183 /* Store the handle in shared memory to be found by index. */
2184 area->control->segment_handles[new_index] =
2185 dsm_segment_handle(segment);
2186 /* Track the highest segment index in the history of the area. */
2187 if (area->control->high_segment_index < new_index)
2188 area->control->high_segment_index = new_index;
2189 /* Track the highest segment index this backend has ever mapped. */
2190 if (area->high_segment_index < new_index)
2191 area->high_segment_index = new_index;
2192 /* Track total size of all segments. */
2196
2197 /* Build a segment map for this segment in this backend. */
2198 segment_map = &area->segment_maps[new_index];
2199 segment_map->segment = segment;
2200 segment_map->mapped_address = dsm_segment_address(segment);
2201 segment_map->header = (dsa_segment_header *) segment_map->mapped_address;
2202 segment_map->fpm = (FreePageManager *)
2203 (segment_map->mapped_address +
2204 MAXALIGN(sizeof(dsa_segment_header)));
2205 segment_map->pagemap = (dsa_pointer *)
2206 (segment_map->mapped_address +
2207 MAXALIGN(sizeof(dsa_segment_header)) +
2208 MAXALIGN(sizeof(FreePageManager)));
2209
2210 /* Set up the free page map. */
2211 FreePageManagerInitialize(segment_map->fpm, segment_map->mapped_address);
2212 FreePageManagerPut(segment_map->fpm, metadata_bytes / FPM_PAGE_SIZE,
2213 usable_pages);
2214
2215 /* Set up the segment header and put it in the appropriate bin. */
2216 segment_map->header->magic =
2217 DSA_SEGMENT_HEADER_MAGIC ^ area->control->handle ^ new_index;
2218 segment_map->header->usable_pages = usable_pages;
2219 segment_map->header->size = total_size;
2220 segment_map->header->bin = contiguous_pages_to_segment_bin(usable_pages);
2221 segment_map->header->prev = DSA_SEGMENT_INDEX_NONE;
2222 segment_map->header->next =
2223 area->control->segment_bins[segment_map->header->bin];
2224 segment_map->header->freed = false;
2225 area->control->segment_bins[segment_map->header->bin] = new_index;
2226 if (segment_map->header->next != DSA_SEGMENT_INDEX_NONE)
2227 {
2229 get_segment_by_index(area, segment_map->header->next);
2230
2231 Assert(next->header->bin == segment_map->header->bin);
2232 next->header->prev = new_index;
2233 }
2234
2235 return segment_map;
2236}
2237
2238/*
2239 * Check if any segments have been freed by destroy_superblock, so we can
2240 * detach from them in this backend. This function is called by
2241 * dsa_get_address and dsa_free to make sure that a dsa_pointer they have
2242 * received can be resolved to the correct segment.
2243 *
2244 * The danger we want to defend against is that there could be an old segment
2245 * mapped into a given slot in this backend, and the dsa_pointer they have
2246 * might refer to some new segment in the same slot. So those functions must
2247 * be sure to process all instructions to detach from a freed segment that had
2248 * been generated by the time this process received the dsa_pointer, before
2249 * they call get_segment_by_index.
2250 */
2251static void
2253{
2254 size_t freed_segment_counter;
2255
2256 /*
2257 * Any other process that has freed a segment has incremented
2258 * freed_segment_counter while holding an LWLock, and that must precede
2259 * any backend creating a new segment in the same slot while holding an
2260 * LWLock, and that must precede the creation of any dsa_pointer pointing
2261 * into the new segment which might reach us here, and the caller must
2262 * have sent the dsa_pointer to this process using appropriate memory
2263 * synchronization (some kind of locking or atomic primitive or system
2264 * call). So all we need to do on the reading side is ask for the load of
2265 * freed_segment_counter to follow the caller's load of the dsa_pointer it
2266 * has, and we can be sure to detect any segments that had been freed as
2267 * of the time that the dsa_pointer reached this process.
2268 */
2270 freed_segment_counter = area->control->freed_segment_counter;
2271 if (unlikely(area->freed_segment_counter != freed_segment_counter))
2272 {
2273 /* Check all currently mapped segments to find what's been freed. */
2277 }
2278}
2279
2280/*
2281 * Workhorse for check_for_freed_segments(), and also used directly in path
2282 * where the area lock is already held. This should be called after acquiring
2283 * the lock but before looking up any segment by index number, to make sure we
2284 * unmap any stale segments that might have previously had the same index as a
2285 * current segment.
2286 */
2287static void
2289{
2290 size_t freed_segment_counter;
2291 int i;
2292
2294 freed_segment_counter = area->control->freed_segment_counter;
2295 if (unlikely(area->freed_segment_counter != freed_segment_counter))
2296 {
2297 for (i = 0; i <= area->high_segment_index; ++i)
2298 {
2299 if (area->segment_maps[i].header != NULL &&
2300 area->segment_maps[i].header->freed)
2301 {
2303 area->segment_maps[i].segment = NULL;
2304 area->segment_maps[i].header = NULL;
2305 area->segment_maps[i].mapped_address = NULL;
2306 }
2307 }
2308 area->freed_segment_counter = freed_segment_counter;
2309 }
2310}
2311
2312/*
2313 * Re-bin segment if it's no longer in the appropriate bin.
2314 */
2315static void
2317{
2318 size_t new_bin;
2319 dsa_segment_index segment_index;
2320
2321 new_bin = contiguous_pages_to_segment_bin(fpm_largest(segment_map->fpm));
2322 if (segment_map->header->bin == new_bin)
2323 return;
2324
2325 /* Remove it from its current bin. */
2326 unlink_segment(area, segment_map);
2327
2328 /* Push it onto the front of its new bin. */
2329 segment_index = get_segment_index(area, segment_map);
2330 segment_map->header->prev = DSA_SEGMENT_INDEX_NONE;
2331 segment_map->header->next = area->control->segment_bins[new_bin];
2332 segment_map->header->bin = new_bin;
2333 area->control->segment_bins[new_bin] = segment_index;
2334 if (segment_map->header->next != DSA_SEGMENT_INDEX_NONE)
2335 {
2337
2338 next = get_segment_by_index(area, segment_map->header->next);
2339 Assert(next->header->bin == new_bin);
2340 next->header->prev = segment_index;
2341 }
2342}
#define pg_read_barrier()
Definition: atomics.h:156
static int32 next
Definition: blutils.c:221
#define Min(x, y)
Definition: c.h:961
#define MAXALIGN(LEN)
Definition: c.h:768
uint8_t uint8
Definition: c.h:486
#define Assert(condition)
Definition: c.h:815
uint16_t uint16
Definition: c.h:487
#define unlikely(x)
Definition: c.h:333
uint32_t uint32
Definition: c.h:488
#define lengthof(array)
Definition: c.h:745
#define fprintf(file, fmt, msg)
Definition: cubescan.l:21
static void unlink_segment(dsa_area *area, dsa_segment_map *segment_map)
Definition: dsa.c:1978
static void check_for_freed_segments(dsa_area *area)
Definition: dsa.c:2252
static const uint16 dsa_size_classes[]
Definition: dsa.c:225
#define DSA_EXTRACT_SEGMENT_NUMBER(dp)
Definition: dsa.c:96
#define DSA_AREA_LOCK(area)
Definition: dsa.c:132
#define DSA_NUM_SEGMENTS_AT_EACH_SIZE
Definition: dsa.c:69
static void add_span_to_fullness_class(dsa_area *area, dsa_area_span *span, dsa_pointer span_pointer, int fclass)
Definition: dsa.c:1929
static bool ensure_active_superblock(dsa_area *area, dsa_area_pool *pool, int size_class)
Definition: dsa.c:1560
#define DSA_SEGMENT_INDEX_NONE
Definition: dsa.c:105
static dsa_area * create_internal(void *place, size_t size, int tranche_id, dsm_handle control_handle, dsm_segment *control_segment, size_t init_segment_size, size_t max_segment_size)
Definition: dsa.c:1218
dsa_area * dsa_attach(dsa_handle handle)
Definition: dsa.c:510
#define DSA_SEGMENT_HEADER_MAGIC
Definition: dsa.c:89
void dsa_trim(dsa_area *area)
Definition: dsa.c:1043
#define DSA_SPAN_NOTHING_FREE
Definition: dsa.c:375
#define DSA_MAKE_POINTER(segment_number, offset)
Definition: dsa.c:92
dsa_area * dsa_create_in_place_ext(void *place, size_t size, int tranche_id, dsm_segment *segment, size_t init_segment_size, size_t max_segment_size)
Definition: dsa.c:471
#define get_segment_index(area, segment_map_ptr)
Definition: dsa.c:379
dsa_area * dsa_attach_in_place(void *place, dsm_segment *segment)
Definition: dsa.c:545
void * dsa_get_address(dsa_area *area, dsa_pointer dp)
Definition: dsa.c:942
void dsa_on_shmem_exit_release_in_place(int code, Datum place)
Definition: dsa.c:590
void dsa_on_dsm_detach_release_in_place(dsm_segment *segment, Datum place)
Definition: dsa.c:576
static dsa_pointer alloc_object(dsa_area *area, int size_class)
Definition: dsa.c:1472
#define DSA_PAGES_PER_SUPERBLOCK
Definition: dsa.c:82
#define DSA_SIZE_CLASS_MAP_QUANTUM
Definition: dsa.c:258
static size_t contiguous_pages_to_segment_bin(size_t n)
Definition: dsa.c:119
static const uint8 dsa_size_class_map[]
Definition: dsa.c:248
dsa_pointer dsa_allocate_extended(dsa_area *area, size_t size, int flags)
Definition: dsa.c:671
static dsa_segment_map * make_new_segment(dsa_area *area, size_t requested_pages)
Definition: dsa.c:2081
size_t dsa_get_total_size(dsa_area *area)
Definition: dsa.c:1027
#define DSA_SUPERBLOCK_SIZE
Definition: dsa.c:376
#define DsaAreaPoolToDsaPointer(area, p)
Definition: dsa.c:322
static void check_for_freed_segments_locked(dsa_area *area)
Definition: dsa.c:2288
#define DSA_EXTRACT_OFFSET(dp)
Definition: dsa.c:99
dsa_area * dsa_create_ext(int tranche_id, size_t init_segment_size, size_t max_segment_size)
Definition: dsa.c:421
static void destroy_superblock(dsa_area *area, dsa_pointer span_pointer)
Definition: dsa.c:1837
#define DSA_MAX_SEGMENTS
Definition: dsa.c:75
size_t dsa_segment_index
Definition: dsa.c:102
static void rebin_segment(dsa_area *area, dsa_segment_map *segment_map)
Definition: dsa.c:2316
#define DSA_SCLASS_LOCK(area, sclass)
Definition: dsa.c:133
void dsa_release_in_place(void *place)
Definition: dsa.c:605
static dsa_segment_map * get_segment_by_index(dsa_area *area, dsa_segment_index index)
Definition: dsa.c:1757
void dsa_set_size_limit(dsa_area *area, size_t limit)
Definition: dsa.c:1018
#define DSA_SCLASS_BLOCK_OF_SPANS
Definition: dsa.c:239
static bool transfer_first_span(dsa_area *area, dsa_area_pool *pool, int fromclass, int toclass)
Definition: dsa.c:1432
static void unlink_span(dsa_area *area, dsa_area_span *span)
Definition: dsa.c:1906
#define DSA_SCLASS_SPAN_LARGE
Definition: dsa.c:240
#define DSA_NUM_SIZE_CLASSES
Definition: dsa.c:236
void dsa_unpin(dsa_area *area)
Definition: dsa.c:994
void dsa_pin_mapping(dsa_area *area)
Definition: dsa.c:635
static dsa_area * attach_internal(void *place, dsm_segment *segment, dsa_handle handle)
Definition: dsa.c:1326
#define NextFreeObjectIndex(object)
Definition: dsa.c:202
void dsa_dump(dsa_area *area)
Definition: dsa.c:1088
dsa_handle dsa_get_handle(dsa_area *area)
Definition: dsa.c:498
static void init_span(dsa_area *area, dsa_pointer span_pointer, dsa_area_pool *pool, dsa_pointer start, size_t npages, uint16 size_class)
Definition: dsa.c:1377
void dsa_detach(dsa_area *area)
Definition: dsa.c:1952
static dsa_segment_map * get_best_segment(dsa_area *area, size_t npages)
Definition: dsa.c:2010
#define DSA_FULLNESS_CLASSES
Definition: dsa.c:266
void dsa_free(dsa_area *area, dsa_pointer dp)
Definition: dsa.c:826
#define DSA_NUM_SEGMENT_BINS
Definition: dsa.c:111
size_t dsa_minimum_size(void)
Definition: dsa.c:1196
void dsa_pin(dsa_area *area)
Definition: dsa.c:975
uint64 dsa_pointer
Definition: dsa.h:62
#define DSA_POINTER_FORMAT
Definition: dsa.h:69
#define DSA_MIN_SEGMENT_SIZE
Definition: dsa.h:100
dsm_handle dsa_handle
Definition: dsa.h:136
#define InvalidDsaPointer
Definition: dsa.h:78
#define DSA_ALLOC_NO_OOM
Definition: dsa.h:74
#define DSA_HANDLE_INVALID
Definition: dsa.h:139
#define DsaPointerIsValid(x)
Definition: dsa.h:106
#define DSA_MAX_SEGMENT_SIZE
Definition: dsa.h:103
#define DSA_ALLOC_HUGE
Definition: dsa.h:73
#define DSA_ALLOC_ZERO
Definition: dsa.h:75
dsm_handle dsm_segment_handle(dsm_segment *seg)
Definition: dsm.c:1123
void dsm_detach(dsm_segment *seg)
Definition: dsm.c:803
void on_dsm_detach(dsm_segment *seg, on_dsm_detach_callback function, Datum arg)
Definition: dsm.c:1132
void dsm_pin_mapping(dsm_segment *seg)
Definition: dsm.c:915
void dsm_unpin_segment(dsm_handle handle)
Definition: dsm.c:988
void dsm_pin_segment(dsm_segment *seg)
Definition: dsm.c:955
void * dsm_segment_address(dsm_segment *seg)
Definition: dsm.c:1095
dsm_segment * dsm_create(Size size, int flags)
Definition: dsm.c:516
dsm_segment * dsm_attach(dsm_handle h)
Definition: dsm.c:665
uint32 dsm_handle
Definition: dsm_impl.h:55
#define DSM_HANDLE_INVALID
Definition: dsm_impl.h:58
int errdetail(const char *fmt,...)
Definition: elog.c:1203
int errcode(int sqlerrcode)
Definition: elog.c:853
int errmsg(const char *fmt,...)
Definition: elog.c:1070
#define FATAL
Definition: elog.h:41
#define ERROR
Definition: elog.h:39
#define elog(elevel,...)
Definition: elog.h:225
#define ereport(elevel,...)
Definition: elog.h:149
bool FreePageManagerGet(FreePageManager *fpm, Size npages, Size *first_page)
Definition: freepage.c:210
void FreePageManagerPut(FreePageManager *fpm, Size first_page, Size npages)
Definition: freepage.c:379
void FreePageManagerInitialize(FreePageManager *fpm, char *base)
Definition: freepage.c:183
#define fpm_largest(fpm)
Definition: freepage.h:88
#define fpm_size_to_pages(sz)
Definition: freepage.h:74
#define FPM_PAGE_SIZE
Definition: freepage.h:30
return str start
int j
Definition: isn.c:73
int i
Definition: isn.c:72
bool LWLockHeldByMe(LWLock *lock)
Definition: lwlock.c:1893
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1168
void LWLockRelease(LWLock *lock)
Definition: lwlock.c:1781
void LWLockInitialize(LWLock *lock, int tranche_id)
Definition: lwlock.c:707
@ LW_EXCLUSIVE
Definition: lwlock.h:114
void pfree(void *pointer)
Definition: mcxt.c:1521
void * palloc(Size size)
Definition: mcxt.c:1317
#define AllocHugeSizeIsValid(size)
Definition: memutils.h:49
#define AllocSizeIsValid(size)
Definition: memutils.h:42
#define pg_leftmost_one_pos_size_t
Definition: pg_bitutils.h:414
static int64 total_size
Definition: pg_checksums.c:62
static Datum PointerGetDatum(const void *X)
Definition: postgres.h:327
uintptr_t Datum
Definition: postgres.h:69
static Pointer DatumGetPointer(Datum X)
Definition: postgres.h:317
ResourceOwner CurrentResourceOwner
Definition: resowner.c:165
static pg_noinline void Size size
Definition: slab.c:607
Definition: lwlock.h:42
dsa_segment_header segment_header
Definition: dsa.c:290
size_t init_segment_size
Definition: dsa.c:300
size_t total_segment_size
Definition: dsa.c:304
int lwlock_tranche_id
Definition: dsa.c:316
size_t max_segment_size
Definition: dsa.c:302
dsa_segment_index high_segment_index
Definition: dsa.c:308
bool pinned
Definition: dsa.c:312
size_t max_total_segment_size
Definition: dsa.c:306
dsa_segment_index segment_bins[DSA_NUM_SEGMENT_BINS]
Definition: dsa.c:296
dsa_area_pool pools[DSA_NUM_SIZE_CLASSES]
Definition: dsa.c:298
size_t freed_segment_counter
Definition: dsa.c:314
int refcnt
Definition: dsa.c:310
LWLock lock
Definition: dsa.c:318
dsa_handle handle
Definition: dsa.c:292
dsm_handle segment_handles[DSA_MAX_SEGMENTS]
Definition: dsa.c:294
dsa_pointer spans[DSA_FULLNESS_CLASSES]
Definition: dsa.c:279
LWLock lock
Definition: dsa.c:277
dsa_pointer nextspan
Definition: dsa.c:187
uint16 fclass
Definition: dsa.c:195
dsa_pointer start
Definition: dsa.c:188
uint16 nallocatable
Definition: dsa.c:192
dsa_pointer prevspan
Definition: dsa.c:186
uint16 size_class
Definition: dsa.c:190
uint16 nmax
Definition: dsa.c:194
uint16 ninitialized
Definition: dsa.c:191
uint16 firstfree
Definition: dsa.c:193
dsa_pointer pool
Definition: dsa.c:185
size_t npages
Definition: dsa.c:189
Definition: dsa.c:348
dsa_segment_map segment_maps[DSA_MAX_SEGMENTS]
Definition: dsa.c:366
dsa_segment_index high_segment_index
Definition: dsa.c:369
size_t freed_segment_counter
Definition: dsa.c:372
dsa_area_control * control
Definition: dsa.c:350
ResourceOwner resowner
Definition: dsa.c:358
uint32 magic
Definition: dsa.c:143
size_t size
Definition: dsa.c:147
dsa_segment_index next
Definition: dsa.c:159
dsa_segment_index prev
Definition: dsa.c:153
size_t usable_pages
Definition: dsa.c:145
size_t bin
Definition: dsa.c:161
dsa_segment_header * header
Definition: dsa.c:336
FreePageManager * fpm
Definition: dsa.c:337
dsm_segment * segment
Definition: dsa.c:334
dsa_pointer * pagemap
Definition: dsa.c:338
char * mapped_address
Definition: dsa.c:335
Definition: type.h:96