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Trust ARC_BUF_SHARED() more
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In my understanding ARC_BUF_SHARED() and arc_buf_is_shared() should
return identical results, except the second also asserts it deeper.
The first is much cheaper though, saving few pointer dereferences.
Replace production arc_buf_is_shared() calls with ARC_BUF_SHARED(),
and call arc_buf_is_shared() in random assertions, while making it
even more strict.

On my tests this in half reduces arc_buf_destroy_impl() time, that
noticeably reduces hash_lock congestion under heavy dbuf eviction.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes #15397
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@amotin
amotin authored Oct 20, 2023
1 parent 4fbc524 commit 57b4098
Showing 1 changed file with 24 additions and 17 deletions.
41 changes: 24 additions & 17 deletions module/zfs/arc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1364,7 +1364,7 @@ arc_buf_is_shared(arc_buf_t *buf)
abd_is_linear(buf->b_hdr->b_l1hdr.b_pabd) &&
buf->b_data == abd_to_buf(buf->b_hdr->b_l1hdr.b_pabd));
IMPLY(shared, HDR_SHARED_DATA(buf->b_hdr));
IMPLY(shared, ARC_BUF_SHARED(buf));
EQUIV(shared, ARC_BUF_SHARED(buf));
IMPLY(shared, ARC_BUF_COMPRESSED(buf) || ARC_BUF_LAST(buf));

/*
Expand Down Expand Up @@ -1998,7 +1998,7 @@ arc_buf_fill(arc_buf_t *buf, spa_t *spa, const zbookmark_phys_t *zb,
IMPLY(encrypted, HDR_ENCRYPTED(hdr));
IMPLY(encrypted, ARC_BUF_ENCRYPTED(buf));
IMPLY(encrypted, ARC_BUF_COMPRESSED(buf));
IMPLY(encrypted, !ARC_BUF_SHARED(buf));
IMPLY(encrypted, !arc_buf_is_shared(buf));

/*
* If the caller wanted encrypted data we just need to copy it from
Expand Down Expand Up @@ -2066,7 +2066,9 @@ arc_buf_fill(arc_buf_t *buf, spa_t *spa, const zbookmark_phys_t *zb,
}

if (hdr_compressed == compressed) {
if (!arc_buf_is_shared(buf)) {
if (ARC_BUF_SHARED(buf)) {
ASSERT(arc_buf_is_shared(buf));
} else {
abd_copy_to_buf(buf->b_data, hdr->b_l1hdr.b_pabd,
arc_buf_size(buf));
}
Expand All @@ -2078,7 +2080,7 @@ arc_buf_fill(arc_buf_t *buf, spa_t *spa, const zbookmark_phys_t *zb,
* If the buf is sharing its data with the hdr, unlink it and
* allocate a new data buffer for the buf.
*/
if (arc_buf_is_shared(buf)) {
if (ARC_BUF_SHARED(buf)) {
ASSERT(ARC_BUF_COMPRESSED(buf));

/* We need to give the buf its own b_data */
Expand All @@ -2090,6 +2092,8 @@ arc_buf_fill(arc_buf_t *buf, spa_t *spa, const zbookmark_phys_t *zb,
/* Previously overhead was 0; just add new overhead */
ARCSTAT_INCR(arcstat_overhead_size, HDR_GET_LSIZE(hdr));
} else if (ARC_BUF_COMPRESSED(buf)) {
ASSERT(!arc_buf_is_shared(buf));

/* We need to reallocate the buf's b_data */
arc_free_data_buf(hdr, buf->b_data, HDR_GET_PSIZE(hdr),
buf);
Expand Down Expand Up @@ -2217,7 +2221,7 @@ arc_evictable_space_increment(arc_buf_hdr_t *hdr, arc_state_t *state)

for (arc_buf_t *buf = hdr->b_l1hdr.b_buf; buf != NULL;
buf = buf->b_next) {
if (arc_buf_is_shared(buf))
if (ARC_BUF_SHARED(buf))
continue;
(void) zfs_refcount_add_many(&state->arcs_esize[type],
arc_buf_size(buf), buf);
Expand Down Expand Up @@ -2256,7 +2260,7 @@ arc_evictable_space_decrement(arc_buf_hdr_t *hdr, arc_state_t *state)

for (arc_buf_t *buf = hdr->b_l1hdr.b_buf; buf != NULL;
buf = buf->b_next) {
if (arc_buf_is_shared(buf))
if (ARC_BUF_SHARED(buf))
continue;
(void) zfs_refcount_remove_many(&state->arcs_esize[type],
arc_buf_size(buf), buf);
Expand Down Expand Up @@ -2481,7 +2485,7 @@ arc_change_state(arc_state_t *new_state, arc_buf_hdr_t *hdr)
* add to the refcount if the arc_buf_t is
* not shared.
*/
if (arc_buf_is_shared(buf))
if (ARC_BUF_SHARED(buf))
continue;

(void) zfs_refcount_add_many(
Expand Down Expand Up @@ -2537,7 +2541,7 @@ arc_change_state(arc_state_t *new_state, arc_buf_hdr_t *hdr)
* add to the refcount if the arc_buf_t is
* not shared.
*/
if (arc_buf_is_shared(buf))
if (ARC_BUF_SHARED(buf))
continue;

(void) zfs_refcount_remove_many(
Expand Down Expand Up @@ -3061,9 +3065,10 @@ arc_buf_destroy_impl(arc_buf_t *buf)
arc_cksum_verify(buf);
arc_buf_unwatch(buf);

if (arc_buf_is_shared(buf)) {
if (ARC_BUF_SHARED(buf)) {
arc_hdr_clear_flags(hdr, ARC_FLAG_SHARED_DATA);
} else {
ASSERT(!arc_buf_is_shared(buf));
uint64_t size = arc_buf_size(buf);
arc_free_data_buf(hdr, buf->b_data, size, buf);
ARCSTAT_INCR(arcstat_overhead_size, -size);
Expand Down Expand Up @@ -3104,9 +3109,9 @@ arc_buf_destroy_impl(arc_buf_t *buf)
*/
if (lastbuf != NULL && !ARC_BUF_ENCRYPTED(lastbuf)) {
/* Only one buf can be shared at once */
VERIFY(!arc_buf_is_shared(lastbuf));
ASSERT(!arc_buf_is_shared(lastbuf));
/* hdr is uncompressed so can't have compressed buf */
VERIFY(!ARC_BUF_COMPRESSED(lastbuf));
ASSERT(!ARC_BUF_COMPRESSED(lastbuf));

ASSERT3P(hdr->b_l1hdr.b_pabd, !=, NULL);
arc_hdr_free_abd(hdr, B_FALSE);
Expand Down Expand Up @@ -6189,7 +6194,7 @@ arc_release(arc_buf_t *buf, const void *tag)
ASSERT(hdr->b_l1hdr.b_buf != buf || buf->b_next != NULL);
VERIFY3S(remove_reference(hdr, tag), >, 0);

if (arc_buf_is_shared(buf) && !ARC_BUF_COMPRESSED(buf)) {
if (ARC_BUF_SHARED(buf) && !ARC_BUF_COMPRESSED(buf)) {
ASSERT3P(hdr->b_l1hdr.b_buf, !=, buf);
ASSERT(ARC_BUF_LAST(buf));
}
Expand All @@ -6206,9 +6211,9 @@ arc_release(arc_buf_t *buf, const void *tag)
* If the current arc_buf_t and the hdr are sharing their data
* buffer, then we must stop sharing that block.
*/
if (arc_buf_is_shared(buf)) {
if (ARC_BUF_SHARED(buf)) {
ASSERT3P(hdr->b_l1hdr.b_buf, !=, buf);
VERIFY(!arc_buf_is_shared(lastbuf));
ASSERT(!arc_buf_is_shared(lastbuf));

/*
* First, sever the block sharing relationship between
Expand Down Expand Up @@ -6241,7 +6246,7 @@ arc_release(arc_buf_t *buf, const void *tag)
*/
ASSERT(arc_buf_is_shared(lastbuf) ||
arc_hdr_get_compress(hdr) != ZIO_COMPRESS_OFF);
ASSERT(!ARC_BUF_SHARED(buf));
ASSERT(!arc_buf_is_shared(buf));
}

ASSERT(hdr->b_l1hdr.b_pabd != NULL || HDR_HAS_RABD(hdr));
Expand Down Expand Up @@ -6335,9 +6340,10 @@ arc_write_ready(zio_t *zio)
arc_cksum_free(hdr);
arc_buf_unwatch(buf);
if (hdr->b_l1hdr.b_pabd != NULL) {
if (arc_buf_is_shared(buf)) {
if (ARC_BUF_SHARED(buf)) {
arc_unshare_buf(hdr, buf);
} else {
ASSERT(!arc_buf_is_shared(buf));
arc_hdr_free_abd(hdr, B_FALSE);
}
}
Expand Down Expand Up @@ -6636,9 +6642,10 @@ arc_write(zio_t *pio, spa_t *spa, uint64_t txg,
* The hdr will remain with a NULL data pointer and the
* buf will take sole ownership of the block.
*/
if (arc_buf_is_shared(buf)) {
if (ARC_BUF_SHARED(buf)) {
arc_unshare_buf(hdr, buf);
} else {
ASSERT(!arc_buf_is_shared(buf));
arc_hdr_free_abd(hdr, B_FALSE);
}
VERIFY3P(buf->b_data, !=, NULL);
Expand Down

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