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Decouple arc_read_done callback from arc buf instantiation

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Add ARC_FLAG_NO_BUF to indicate that a buffer need not be
instantiated.  This fixes a ~20% performance regression on
cached reads due to zfetch changes.

Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #11220 
Closes #11232
This commit is contained in:
Matthew Macy
2020-12-09 15:05:06 -08:00
committed by GitHub
parent edb20ff3ba
commit 1e4732cbda
3 changed files with 10 additions and 3 deletions
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module/zfs/arc.c
+3 -2
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@@ -5924,6 +5924,7 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
boolean_t noauth_read = BP_IS_AUTHENTICATED(bp) &&
(zio_flags & ZIO_FLAG_RAW_ENCRYPT) != 0;
boolean_t embedded_bp = !!BP_IS_EMBEDDED(bp);
boolean_t no_buf = *arc_flags & ARC_FLAG_NO_BUF;
int rc = 0;
ASSERT(!embedded_bp ||
@@ -5998,7 +5999,7 @@ top:
}
ASSERT(*arc_flags & ARC_FLAG_NOWAIT);
if (done) {
if (done && !no_buf) {
arc_callback_t *acb = NULL;
acb = kmem_zalloc(sizeof (arc_callback_t),
@@ -6027,7 +6028,7 @@ top:
ASSERT(hdr->b_l1hdr.b_state == arc_mru ||
hdr->b_l1hdr.b_state == arc_mfu);
if (done) {
if (done && !no_buf) {
if (hdr->b_flags & ARC_FLAG_PREDICTIVE_PREFETCH) {
/*
* This is a demand read which does not have to