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Redispatch ZIOs in deep call graphs #2786

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Redispatch ZIOs in deep call graphs #2786

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1 change: 1 addition & 0 deletions include/sys/zio.h
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Original file line number Diff line number Diff line change
Expand Up @@ -440,6 +440,7 @@ struct zio {
uint64_t io_child_count;
uint64_t io_phys_children;
uint64_t io_parent_count;
uint64_t io_recursion_count;
uint64_t *io_stall;
zio_t *io_gang_leader;
zio_gang_node_t *io_gang_tree;
Expand Down
9 changes: 6 additions & 3 deletions module/zfs/vdev_queue.c
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Expand Up @@ -650,6 +650,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
}

zio_add_child(dio, aio);
dio->io_recursion_count = aio->io_recursion_count + 1;
vdev_queue_io_remove(vq, dio);
zio_vdev_io_bypass(dio);
zio_execute(dio);
Expand All @@ -661,7 +662,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
}

static zio_t *
vdev_queue_io_to_issue(vdev_queue_t *vq)
vdev_queue_io_to_issue(vdev_queue_t *vq, uint64_t recursion_count)
{
zio_t *zio, *aio;
zio_priority_t p;
Expand Down Expand Up @@ -708,6 +709,7 @@ vdev_queue_io_to_issue(vdev_queue_t *vq)
*/
if (zio->io_flags & ZIO_FLAG_NODATA) {
mutex_exit(&vq->vq_lock);
zio->io_recursion_count = recursion_count + 1;
zio_vdev_io_bypass(zio);
zio_execute(zio);
mutex_enter(&vq->vq_lock);
Expand Down Expand Up @@ -750,7 +752,7 @@ vdev_queue_io(zio_t *zio)
mutex_enter(&vq->vq_lock);
zio->io_timestamp = gethrtime();
vdev_queue_io_add(vq, zio);
nio = vdev_queue_io_to_issue(vq);
nio = vdev_queue_io_to_issue(vq, zio->io_recursion_count);
mutex_exit(&vq->vq_lock);

if (nio == NULL)
Expand Down Expand Up @@ -781,7 +783,8 @@ vdev_queue_io_done(zio_t *zio)
vq->vq_io_complete_ts = gethrtime();
vq->vq_io_delta_ts = vq->vq_io_complete_ts - zio->io_timestamp;

while ((nio = vdev_queue_io_to_issue(vq)) != NULL) {
while ((nio = vdev_queue_io_to_issue(vq, zio->io_recursion_count))
!= NULL) {
mutex_exit(&vq->vq_lock);
if (nio->io_done == vdev_queue_agg_io_done) {
zio_nowait(nio);
Expand Down
17 changes: 17 additions & 0 deletions module/zfs/zio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,7 @@ kmem_cache_t *zio_buf_cache[SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT];
kmem_cache_t *zio_data_buf_cache[SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT];
int zio_bulk_flags = 0;
int zio_delay_max = ZIO_DELAY_MAX;
int zio_recursion_threshold = 16; /* Threshold to redispatch zio_t objects */

/*
* The following actions directly effect the spa's sync-to-convergence logic.
Expand Down Expand Up @@ -516,6 +517,7 @@ zio_notify_parent(zio_t *pio, zio_t *zio, enum zio_wait_type wait)

if (*countp == 0 && pio->io_stall == countp) {
pio->io_stall = NULL;
pio->io_recursion_count = zio->io_recursion_count + 1;
mutex_exit(&pio->io_lock);
__zio_execute(pio);
} else {
Expand Down Expand Up @@ -975,6 +977,8 @@ zio_vdev_child_io(zio_t *pio, blkptr_t *bp, vdev_t *vd, uint64_t offset,
if (vd->vdev_ops->vdev_op_leaf && zio->io_logical != NULL)
zio->io_logical->io_phys_children++;

zio->io_recursion_count = pio->io_recursion_count + 1;

return (zio);
}

Expand Down Expand Up @@ -1268,6 +1272,9 @@ zio_taskq_dispatch(zio_t *zio, zio_taskq_type_t q, boolean_t cutinline)
zio_type_t t = zio->io_type;
int flags = (cutinline ? TQ_FRONT : 0);

/* Reset the notify counter */
zio->io_recursion_count = 0;

/*
* If we're a config writer or a probe, the normal issue and
* interrupt threads may all be blocked waiting for the config lock.
Expand Down Expand Up @@ -1391,6 +1398,16 @@ __zio_execute(zio_t *zio)
cut = (stage == ZIO_STAGE_VDEV_IO_START) ?
zio_requeue_io_start_cut_in_line : B_FALSE;

/*
* Deep call graphs can cause us to overrun the stack.
* Redispatch ZIO when we hit zio_recursion_threshold.
*/
if (zio->io_recursion_count &&
(zio->io_recursion_count >= zio_recursion_threshold)) {
zio_taskq_dispatch(zio, ZIO_TASKQ_ISSUE, B_TRUE);
return;
}

/*
* If we are in interrupt context and this pipeline stage
* will grab a config lock that is held across I/O,
Expand Down