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Fix ARC stats for embedded blkptrs

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Re-factor arc_read() to better account for embedded data blkptrs.
Previously, reading the payload from an embedded blkptr would cause
arcstats such as demand_metadata_misses to be bumped when there was
actually no cache "miss" because the data are already available in
the blkptr.

The following test procedure was used to demonstrate the problem:

   zpool create tank ...
   zfs create -o compression=lz4 tank/fs
   echo blah > /tank/fs/blah
   stat /tank/fs/blah
   grep 'meta.*mis' /proc/spl/kstat/zfs/arcstats

and repeating the last two steps to watch the metadata miss counter
increment.  This can also be demonstrated via the  zfs_arc_miss DTRACE4
probe in arc_read().

Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed-by: George Wilson <george.wilson@delphix.com>
Reviewed-by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes #8319
This commit is contained in:
Tim Chase 2019-02-04 11:33:30 -06:00 committed by Brian Behlendorf
parent 9634299657
commit 0902c4577f
1 changed files with 32 additions and 15 deletions
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47
module/zfs/arc.c
View File

@ -6147,13 +6147,14 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
(zio_flags & ZIO_FLAG_RAW_ENCRYPT) != 0;
boolean_t noauth_read = BP_IS_AUTHENTICATED(bp) &&
(zio_flags & ZIO_FLAG_RAW_ENCRYPT) != 0;
boolean_t embedded_bp = !!BP_IS_EMBEDDED(bp);
int rc = 0;
ASSERT(!BP_IS_EMBEDDED(bp) ||
ASSERT(!embedded_bp ||
BPE_GET_ETYPE(bp) == BP_EMBEDDED_TYPE_DATA);
top:
if (!BP_IS_EMBEDDED(bp)) {
if (!embedded_bp) {
/*
* Embedded BP's have no DVA and require no I/O to "read".
* Create an anonymous arc buf to back it.
@ -6253,7 +6254,7 @@ top:
ARC_FLAG_PRESCIENT_PREFETCH);
}
ASSERT(!BP_IS_EMBEDDED(bp) || !BP_IS_HOLE(bp));
ASSERT(!embedded_bp || !BP_IS_HOLE(bp));
/* Get a buf with the desired data in it. */
rc = arc_buf_alloc_impl(hdr, spa, zb, private,
@ -6321,14 +6322,17 @@ top:
}
if (hdr == NULL) {
/* this block is not in the cache */
/*
* This block is not in the cache or it has
* embedded data.
*/
arc_buf_hdr_t *exists = NULL;
arc_buf_contents_t type = BP_GET_BUFC_TYPE(bp);
hdr = arc_hdr_alloc(spa_load_guid(spa), psize, lsize,
BP_IS_PROTECTED(bp), BP_GET_COMPRESS(bp), type,
encrypted_read);
if (!BP_IS_EMBEDDED(bp)) {
if (!embedded_bp) {
hdr->b_dva = *BP_IDENTITY(bp);
hdr->b_birth = BP_PHYSICAL_BIRTH(bp);
exists = buf_hash_insert(hdr, &hash_lock);
@ -6465,17 +6469,25 @@ top:
arc_hdr_clear_flags(hdr, ARC_FLAG_PRIO_ASYNC_READ);
/*
* At this point, we have a level 1 cache miss. Try again in
* L2ARC if possible.
* At this point, we have a level 1 cache miss or a blkptr
* with embedded data. Try again in L2ARC if possible.
*/
ASSERT3U(HDR_GET_LSIZE(hdr), ==, lsize);
DTRACE_PROBE4(arc__miss, arc_buf_hdr_t *, hdr, blkptr_t *, bp,
uint64_t, lsize, zbookmark_phys_t *, zb);
ARCSTAT_BUMP(arcstat_misses);
ARCSTAT_CONDSTAT(!HDR_PREFETCH(hdr),
demand, prefetch, !HDR_ISTYPE_METADATA(hdr),
data, metadata, misses);
/*
* Skip ARC stat bump for block pointers with embedded
* data. The data are read from the blkptr itself via
* decode_embedded_bp_compressed().
*/
if (!embedded_bp) {
DTRACE_PROBE4(arc__miss, arc_buf_hdr_t *, hdr,
blkptr_t *, bp, uint64_t, lsize,
zbookmark_phys_t *, zb);
ARCSTAT_BUMP(arcstat_misses);
ARCSTAT_CONDSTAT(!HDR_PREFETCH(hdr),
demand, prefetch, !HDR_ISTYPE_METADATA(hdr), data,
metadata, misses);
}
if (vd != NULL && l2arc_ndev != 0 && !(l2arc_norw && devw)) {
/*
@ -6567,7 +6579,12 @@ top:
} else {
if (vd != NULL)
spa_config_exit(spa, SCL_L2ARC, vd);
if (l2arc_ndev != 0) {
/*
* Skip ARC stat bump for block pointers with
* embedded data. The data are read from the blkptr
* itself via decode_embedded_bp_compressed().
*/
if (l2arc_ndev != 0 && !embedded_bp) {
DTRACE_PROBE1(l2arc__miss,
arc_buf_hdr_t *, hdr);
ARCSTAT_BUMP(arcstat_l2_misses);
@ -6592,7 +6609,7 @@ top:
out:
/* embedded bps don't actually go to disk */
if (!BP_IS_EMBEDDED(bp))
if (!embedded_bp)
spa_read_history_add(spa, zb, *arc_flags);
return (rc);
}