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Gang ABD Type

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Adding the gang ABD type, which allows for linear and scatter ABDs to
be chained together into a single ABD.

This can be used to avoid doing memory copies to/from ABDs. An example
of this can be found in vdev_queue.c in the vdev_queue_aggregate()
function.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Brian <bwa@clemson.edu>
Co-authored-by: Mark Maybee <mmaybee@cray.com>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Closes #10069
This commit is contained in:
Brian Atkinson
2020-05-20 19:06:09 -06:00
committed by GitHub
parent 501a1511ae
commit fb822260b1
7 changed files with 629 additions and 106 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/vdev_queue.c
+46 -20
View File
@@ -535,15 +535,6 @@ vdev_queue_pending_remove(vdev_queue_t *vq, zio_t *zio)
static void
vdev_queue_agg_io_done(zio_t *aio)
{
if (aio->io_type == ZIO_TYPE_READ) {
zio_t *pio;
zio_link_t *zl = NULL;
while ((pio = zio_walk_parents(aio, &zl)) != NULL) {
abd_copy_off(pio->io_abd, aio->io_abd,
0, pio->io_offset - aio->io_offset, pio->io_size);
}
}
abd_free(aio->io_abd);
}
@@ -556,6 +547,14 @@ vdev_queue_agg_io_done(zio_t *aio)
#define IO_SPAN(fio, lio) ((lio)->io_offset + (lio)->io_size - (fio)->io_offset)
#define IO_GAP(fio, lio) (-IO_SPAN(lio, fio))
/*
* Sufficiently adjacent io_offset's in ZIOs will be aggregated. We do this
* by creating a gang ABD from the adjacent ZIOs io_abd's. By using
* a gang ABD we avoid doing memory copies to and from the parent,
* child ZIOs. The gang ABD also accounts for gaps between adjacent
* io_offsets by simply getting the zero ABD for writes or allocating
* a new ABD for reads and placing them in the gang ABD as well.
*/
static zio_t *
vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
{
@@ -568,6 +567,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
boolean_t stretch = B_FALSE;
avl_tree_t *t = vdev_queue_type_tree(vq, zio->io_type);
enum zio_flag flags = zio->io_flags & ZIO_FLAG_AGG_INHERIT;
uint64_t next_offset;
abd_t *abd;
maxblocksize = spa_maxblocksize(vq->vq_vdev->vdev_spa);
@@ -695,7 +695,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
size = IO_SPAN(first, last);
ASSERT3U(size, <=, maxblocksize);
abd = abd_alloc_for_io(size, B_TRUE);
abd = abd_alloc_gang_abd();
if (abd == NULL)
return (NULL);
@@ -706,32 +706,58 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
aio->io_timestamp = first->io_timestamp;
nio = first;
next_offset = first->io_offset;
do {
dio = nio;
nio = AVL_NEXT(t, dio);
zio_add_child(dio, aio);
vdev_queue_io_remove(vq, dio);
if (dio->io_offset != next_offset) {
/* allocate a buffer for a read gap */
ASSERT3U(dio->io_type, ==, ZIO_TYPE_READ);
ASSERT3U(dio->io_offset, >, next_offset);
abd = abd_alloc_for_io(
dio->io_offset - next_offset, B_TRUE);
abd_gang_add(aio->io_abd, abd, B_TRUE);
}
if (dio->io_abd &&
(dio->io_size != abd_get_size(dio->io_abd))) {
/* abd size not the same as IO size */
ASSERT3U(abd_get_size(dio->io_abd), >, dio->io_size);
abd = abd_get_offset_size(dio->io_abd, 0, dio->io_size);
abd_gang_add(aio->io_abd, abd, B_TRUE);
} else {
if (dio->io_flags & ZIO_FLAG_NODATA) {
/* allocate a buffer for a write gap */
ASSERT3U(dio->io_type, ==, ZIO_TYPE_WRITE);
ASSERT3P(dio->io_abd, ==, NULL);
abd_gang_add(aio->io_abd,
abd_get_zeros(dio->io_size), B_TRUE);
} else {
/*
* We pass B_FALSE to abd_gang_add()
* because we did not allocate a new
* ABD, so it is assumed the caller
* will free this ABD.
*/
abd_gang_add(aio->io_abd, dio->io_abd,
B_FALSE);
}
}
next_offset = dio->io_offset + dio->io_size;
} while (dio != last);
ASSERT3U(abd_get_size(aio->io_abd), ==, aio->io_size);
/*
* We need to drop the vdev queue's lock during zio_execute() to
* avoid a deadlock that we could encounter due to lock order
* reversal between vq_lock and io_lock in zio_change_priority().
* Use the dropped lock to do memory copy without congestion.
*/
mutex_exit(&vq->vq_lock);
while ((dio = zio_walk_parents(aio, &zl)) != NULL) {
ASSERT3U(dio->io_type, ==, aio->io_type);
if (dio->io_flags & ZIO_FLAG_NODATA) {
ASSERT3U(dio->io_type, ==, ZIO_TYPE_WRITE);
abd_zero_off(aio->io_abd,
dio->io_offset - aio->io_offset, dio->io_size);
} else if (dio->io_type == ZIO_TYPE_WRITE) {
abd_copy_off(aio->io_abd, dio->io_abd,
dio->io_offset - aio->io_offset, 0, dio->io_size);
}
zio_vdev_io_bypass(dio);
zio_execute(dio);
}