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Decouple arc_read_done callback from arc buf instantiation 

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
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 10 additions and 3 deletions
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5
include/sys/arc.h
View File

@ -154,6 +154,11 @@ typedef enum arc_flags
*/
ARC_FLAG_CACHED_ONLY = 1 << 22,
/*
* Don't instantiate an arc_buf_t for arc_read_done.
*/
ARC_FLAG_NO_BUF = 1 << 23,
/*
* The arc buffer's compression mode is stored in the top 7 bits of the
* flags field, so these dummy flags are included so that MDB can

5
module/zfs/arc.c
View File

@ -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

3
module/zfs/dbuf.c
View File

@ -3040,7 +3040,8 @@ dbuf_issue_final_prefetch(dbuf_prefetch_arg_t *dpa, blkptr_t *bp)
int zio_flags = ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE;
arc_flags_t aflags =
dpa->dpa_aflags | ARC_FLAG_NOWAIT | ARC_FLAG_PREFETCH;
dpa->dpa_aflags | ARC_FLAG_NOWAIT | ARC_FLAG_PREFETCH |
ARC_FLAG_NO_BUF;
/* dnodes are always read as raw and then converted later */
if (BP_GET_TYPE(bp) == DMU_OT_DNODE && BP_IS_PROTECTED(bp) &&