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zfetch: Don't issue new streams when old have not completed

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The current dmu_zfetch code implicitly assumes that I/Os complete
within min_sec_reap seconds. With async dmu and a readonly workload
(and thus no exponential backoff in operations from the "write
throttle") such as L2ARC rebuild it is possible to saturate the drives
with I/O requests. These are then effectively compounded with prefetch
requests.

This change reference counts streams and prevents them from being
recycled after their min_sec_reap timeout if they still have
outstanding I/Os.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #10900
This commit is contained in:
Matthew Macy
2020-09-27 17:08:38 -07:00
committed by GitHub
parent cf2667759f
commit af20b97078
4 changed files with 166 additions and 44 deletions
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module/zfs/dbuf.c
+52 -19
View File
@@ -3003,8 +3003,29 @@ typedef struct dbuf_prefetch_arg {
zio_priority_t dpa_prio; /* The priority I/Os should be issued at. */
zio_t *dpa_zio; /* The parent zio_t for all prefetches. */
arc_flags_t dpa_aflags; /* Flags to pass to the final prefetch. */
dbuf_prefetch_fn dpa_cb; /* prefetch completion callback */
void *dpa_arg; /* prefetch completion arg */
} dbuf_prefetch_arg_t;
static void
dbuf_prefetch_fini(dbuf_prefetch_arg_t *dpa, boolean_t io_done)
{
if (dpa->dpa_cb != NULL)
dpa->dpa_cb(dpa->dpa_arg, io_done);
kmem_free(dpa, sizeof (*dpa));
}
static void
dbuf_issue_final_prefetch_done(zio_t *zio, const zbookmark_phys_t *zb,
const blkptr_t *iobp, arc_buf_t *abuf, void *private)
{
dbuf_prefetch_arg_t *dpa = private;
dbuf_prefetch_fini(dpa, B_TRUE);
if (abuf != NULL)
arc_buf_destroy(abuf, private);
}
/*
* Actually issue the prefetch read for the block given.
*/
@@ -3017,7 +3038,7 @@ dbuf_issue_final_prefetch(dbuf_prefetch_arg_t *dpa, blkptr_t *bp)
SPA_FEATURE_REDACTED_DATASETS));
if (BP_IS_HOLE(bp) || BP_IS_EMBEDDED(bp) || BP_IS_REDACTED(bp))
return;
return (dbuf_prefetch_fini(dpa, B_FALSE));
int zio_flags = ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE;
arc_flags_t aflags =
@@ -3031,7 +3052,8 @@ dbuf_issue_final_prefetch(dbuf_prefetch_arg_t *dpa, blkptr_t *bp)
ASSERT3U(dpa->dpa_curlevel, ==, BP_GET_LEVEL(bp));
ASSERT3U(dpa->dpa_curlevel, ==, dpa->dpa_zb.zb_level);
ASSERT(dpa->dpa_zio != NULL);
(void) arc_read(dpa->dpa_zio, dpa->dpa_spa, bp, NULL, NULL,
(void) arc_read(dpa->dpa_zio, dpa->dpa_spa, bp,
dbuf_issue_final_prefetch_done, dpa,
dpa->dpa_prio, zio_flags, &aflags, &dpa->dpa_zb);
}
@@ -3051,8 +3073,7 @@ dbuf_prefetch_indirect_done(zio_t *zio, const zbookmark_phys_t *zb,
if (abuf == NULL) {
ASSERT(zio == NULL || zio->io_error != 0);
kmem_free(dpa, sizeof (*dpa));
return;
return (dbuf_prefetch_fini(dpa, B_TRUE));
}
ASSERT(zio == NULL || zio->io_error == 0);
@@ -3084,11 +3105,9 @@ dbuf_prefetch_indirect_done(zio_t *zio, const zbookmark_phys_t *zb,
dmu_buf_impl_t *db = dbuf_hold_level(dpa->dpa_dnode,
dpa->dpa_curlevel, curblkid, FTAG);
if (db == NULL) {
kmem_free(dpa, sizeof (*dpa));
arc_buf_destroy(abuf, private);
return;
return (dbuf_prefetch_fini(dpa, B_TRUE));
}
(void) dbuf_read(db, NULL,
DB_RF_MUST_SUCCEED | DB_RF_NOPREFETCH | DB_RF_HAVESTRUCT);
dbuf_rele(db, FTAG);
@@ -3105,11 +3124,10 @@ dbuf_prefetch_indirect_done(zio_t *zio, const zbookmark_phys_t *zb,
dpa->dpa_dnode->dn_objset->os_dsl_dataset,
SPA_FEATURE_REDACTED_DATASETS));
if (BP_IS_HOLE(bp) || BP_IS_REDACTED(bp)) {
kmem_free(dpa, sizeof (*dpa));
dbuf_prefetch_fini(dpa, B_TRUE);
} else if (dpa->dpa_curlevel == dpa->dpa_zb.zb_level) {
ASSERT3U(nextblkid, ==, dpa->dpa_zb.zb_blkid);
dbuf_issue_final_prefetch(dpa, bp);
kmem_free(dpa, sizeof (*dpa));
} else {
arc_flags_t iter_aflags = ARC_FLAG_NOWAIT;
zbookmark_phys_t zb;
@@ -3139,9 +3157,10 @@ dbuf_prefetch_indirect_done(zio_t *zio, const zbookmark_phys_t *zb,
* complete. Note that the prefetch might fail if the dataset is encrypted and
* the encryption key is unmapped before the IO completes.
*/
void
dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
arc_flags_t aflags)
int
dbuf_prefetch_impl(dnode_t *dn, int64_t level, uint64_t blkid,
zio_priority_t prio, arc_flags_t aflags, dbuf_prefetch_fn cb,
void *arg)
{
blkptr_t bp;
int epbs, nlevels, curlevel;
@@ -3151,10 +3170,10 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
if (blkid > dn->dn_maxblkid)
return;
goto no_issue;
if (level == 0 && dnode_block_freed(dn, blkid))
return;
goto no_issue;
/*
* This dnode hasn't been written to disk yet, so there's nothing to
@@ -3162,11 +3181,11 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
*/
nlevels = dn->dn_phys->dn_nlevels;
if (level >= nlevels || dn->dn_phys->dn_nblkptr == 0)
return;
goto no_issue;
epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
if (dn->dn_phys->dn_maxblkid < blkid << (epbs * level))
return;
goto no_issue;
dmu_buf_impl_t *db = dbuf_find(dn->dn_objset, dn->dn_object,
level, blkid);
@@ -3176,7 +3195,7 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
* This dbuf already exists. It is either CACHED, or
* (we assume) about to be read or filled.
*/
return;
goto no_issue;
}
/*
@@ -3212,7 +3231,7 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
dsl_dataset_feature_is_active(dn->dn_objset->os_dsl_dataset,
SPA_FEATURE_REDACTED_DATASETS));
if (BP_IS_HOLE(&bp) || BP_IS_REDACTED(&bp))
return;
goto no_issue;
ASSERT3U(curlevel, ==, BP_GET_LEVEL(&bp));
@@ -3230,6 +3249,8 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
dpa->dpa_dnode = dn;
dpa->dpa_epbs = epbs;
dpa->dpa_zio = pio;
dpa->dpa_cb = cb;
dpa->dpa_arg = arg;
/* flag if L2ARC eligible, l2arc_noprefetch then decides */
if (DNODE_LEVEL_IS_L2CACHEABLE(dn, level))
@@ -3245,7 +3266,6 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
if (curlevel == level) {
ASSERT3U(curblkid, ==, blkid);
dbuf_issue_final_prefetch(dpa, &bp);
kmem_free(dpa, sizeof (*dpa));
} else {
arc_flags_t iter_aflags = ARC_FLAG_NOWAIT;
zbookmark_phys_t zb;
@@ -3266,6 +3286,19 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
* dpa may have already been freed.
*/
zio_nowait(pio);
return (1);
no_issue:
if (cb != NULL)
cb(arg, B_FALSE);
return (0);
}
int
dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
arc_flags_t aflags)
{
return (dbuf_prefetch_impl(dn, level, blkid, prio, aflags, NULL, NULL));
}
/*