aio_init.c

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/*-------------------------------------------------------------------------
 *
 * aio_init.c
 *    AIO - Subsystem Initialization
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/storage/aio/aio_init.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "miscadmin.h"
#include "storage/aio.h"
#include "storage/aio_internal.h"
#include "storage/aio_subsys.h"
#include "storage/bufmgr.h"
#include "storage/io_worker.h"
#include "storage/ipc.h"
#include "storage/proc.h"
#include "storage/shmem.h"
#include "storage/subsystems.h"
#include "utils/guc.h"
 
 
static void AioShmemRequest(void *arg);
static void AioShmemInit(void *arg);
static void AioShmemAttach(void *arg);
 
const ShmemCallbacks AioShmemCallbacks = {
    .request_fn = AioShmemRequest,
    .init_fn = AioShmemInit,
    .attach_fn = AioShmemAttach,
};
 
static PgAioBackend *AioBackendShmemPtr;
static PgAioHandle *AioHandleShmemPtr;
static struct iovec *AioHandleIOVShmemPtr;
static uint64 *AioHandleDataShmemPtr;
 
static uint32
AioProcs(void)
{
    /*
     * While AIO workers don't need their own AIO context, we can't currently
     * guarantee that nothing gets assigned to an IO worker's ProcNumber if we
     * just subtracted MAX_IO_WORKERS.
     */
    return MaxBackends + NUM_AUXILIARY_PROCS;
}
 
static Size
AioBackendShmemSize(void)
{
    return mul_size(AioProcs(), sizeof(PgAioBackend));
}
 
static Size
AioHandleShmemSize(void)
{
    Size        sz;
 
    /* verify AioChooseMaxConcurrency() did its thing */
    Assert(io_max_concurrency > 0);
 
    /* io handles */
    sz = mul_size(AioProcs(),
                  mul_size(io_max_concurrency, sizeof(PgAioHandle)));
 
    return sz;
}
 
static Size
AioHandleIOVShmemSize(void)
{
    /* each IO handle can have up to io_max_combine_limit iovec objects */
    return mul_size(sizeof(struct iovec),
                    mul_size(mul_size(io_max_combine_limit, AioProcs()),
                             io_max_concurrency));
}
 
static Size
AioHandleDataShmemSize(void)
{
    /* each buffer referenced by an iovec can have associated data */
    return mul_size(sizeof(uint64),
                    mul_size(mul_size(io_max_combine_limit, AioProcs()),
                             io_max_concurrency));
}
 
/*
 * Choose a suitable value for io_max_concurrency.
 *
 * It's unlikely that we could have more IOs in flight than buffers that we
 * would be allowed to pin.
 *
 * On the upper end, apply a cap too - just because shared_buffers is large,
 * it doesn't make sense have millions of buffers undergo IO concurrently.
 */
static int
AioChooseMaxConcurrency(void)
{
    uint32      max_backends;
    int         max_proportional_pins;
 
    /* Similar logic to LimitAdditionalPins() */
    max_backends = MaxBackends + NUM_AUXILIARY_PROCS;
    max_proportional_pins = NBuffers / max_backends;
 
    max_proportional_pins = Max(max_proportional_pins, 1);
 
    /* apply upper limit */
    return Min(max_proportional_pins, 64);
}
 
/*
 * Register AIO subsystem's shared memory needs.
 */
static void
AioShmemRequest(void *arg)
{
    /*
     * Resolve io_max_concurrency if not already done
     *
     * We prefer to report this value's source as PGC_S_DYNAMIC_DEFAULT.
     * However, if the DBA explicitly set io_max_concurrency = -1 in the
     * config file, then PGC_S_DYNAMIC_DEFAULT will fail to override that and
     * we must force the matter with PGC_S_OVERRIDE.
     */
    if (io_max_concurrency == -1)
    {
        char        buf[32];
 
        snprintf(buf, sizeof(buf), "%d", AioChooseMaxConcurrency());
        SetConfigOption("io_max_concurrency", buf, PGC_POSTMASTER,
                        PGC_S_DYNAMIC_DEFAULT);
        if (io_max_concurrency == -1)   /* failed to apply it? */
            SetConfigOption("io_max_concurrency", buf, PGC_POSTMASTER,
                            PGC_S_OVERRIDE);
    }
 
    ShmemRequestStruct(.name = "AioCtl",
                       .size = sizeof(PgAioCtl),
                       .ptr = (void **) &pgaio_ctl,
        );
 
    ShmemRequestStruct(.name = "AioBackend",
                       .size = AioBackendShmemSize(),
                       .ptr = (void **) &AioBackendShmemPtr,
        );
 
    ShmemRequestStruct(.name = "AioHandle",
                       .size = AioHandleShmemSize(),
                       .ptr = (void **) &AioHandleShmemPtr,
        );
 
    ShmemRequestStruct(.name = "AioHandleIOV",
                       .size = AioHandleIOVShmemSize(),
                       .ptr = (void **) &AioHandleIOVShmemPtr,
        );
 
    ShmemRequestStruct(.name = "AioHandleData",
                       .size = AioHandleDataShmemSize(),
                       .ptr = (void **) &AioHandleDataShmemPtr,
        );
 
    if (pgaio_method_ops->shmem_callbacks.request_fn)
        pgaio_method_ops->shmem_callbacks.request_fn(pgaio_method_ops->shmem_callbacks.opaque_arg);
}
 
/*
 * Initialize AIO shared memory during postmaster startup.
 */
static void
AioShmemInit(void *arg)
{
    uint32      io_handle_off = 0;
    uint32      iovec_off = 0;
    uint32      per_backend_iovecs = io_max_concurrency * io_max_combine_limit;
 
    pgaio_ctl->io_handle_count = AioProcs() * io_max_concurrency;
    pgaio_ctl->iovec_count = AioProcs() * per_backend_iovecs;
 
    pgaio_ctl->backend_state = AioBackendShmemPtr;
    pgaio_ctl->io_handles = AioHandleShmemPtr;
    pgaio_ctl->iovecs = AioHandleIOVShmemPtr;
    pgaio_ctl->handle_data = AioHandleDataShmemPtr;
 
    for (int procno = 0; procno < AioProcs(); procno++)
    {
        PgAioBackend *bs = &pgaio_ctl->backend_state[procno];
 
        bs->io_handle_off = io_handle_off;
        io_handle_off += io_max_concurrency;
 
        dclist_init(&bs->idle_ios);
        memset(bs->staged_ios, 0, sizeof(PgAioHandle *) * PGAIO_SUBMIT_BATCH_SIZE);
        dclist_init(&bs->in_flight_ios);
 
        /* initialize per-backend IOs */
        for (int i = 0; i < io_max_concurrency; i++)
        {
            PgAioHandle *ioh = &pgaio_ctl->io_handles[bs->io_handle_off + i];
 
            ioh->generation = 1;
            ioh->owner_procno = procno;
            ioh->iovec_off = iovec_off;
            ioh->handle_data_len = 0;
            ioh->report_return = NULL;
            ioh->resowner = NULL;
            ioh->num_callbacks = 0;
            ioh->distilled_result.status = PGAIO_RS_UNKNOWN;
            ioh->flags = 0;
 
            ConditionVariableInit(&ioh->cv);
 
            dclist_push_tail(&bs->idle_ios, &ioh->node);
            iovec_off += io_max_combine_limit;
        }
    }
 
    if (pgaio_method_ops->shmem_callbacks.init_fn)
        pgaio_method_ops->shmem_callbacks.init_fn(pgaio_method_ops->shmem_callbacks.opaque_arg);
}
 
static void
AioShmemAttach(void *arg)
{
    if (pgaio_method_ops->shmem_callbacks.attach_fn)
        pgaio_method_ops->shmem_callbacks.attach_fn(pgaio_method_ops->shmem_callbacks.opaque_arg);
}
 
void
pgaio_init_backend(void)
{
    /* shouldn't be initialized twice */
    Assert(!pgaio_my_backend);
 
    if (MyBackendType == B_IO_WORKER)
        return;
 
    if (MyProc == NULL || MyProcNumber >= AioProcs())
        elog(ERROR, "aio requires a normal PGPROC");
 
    pgaio_my_backend = &pgaio_ctl->backend_state[MyProcNumber];
 
    if (pgaio_method_ops->init_backend)
        pgaio_method_ops->init_backend();
 
    before_shmem_exit(pgaio_shutdown, 0);
}