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System-wide speculative prefetch limit. #14516

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merged 1 commit into from
Mar 1, 2023
Merged

System-wide speculative prefetch limit. #14516

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1 change: 1 addition & 0 deletions include/sys/arc_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@
#define _SYS_ARC_IMPL_H

#include <sys/arc.h>
#include <sys/multilist.h>
#include <sys/zio_crypt.h>
#include <sys/zthr.h>
#include <sys/aggsum.h>
Expand Down
29 changes: 24 additions & 5 deletions module/zfs/dmu_zfetch.c
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
*/

#include <sys/zfs_context.h>
#include <sys/arc_impl.h>
#include <sys/dnode.h>
#include <sys/dmu_objset.h>
#include <sys/dmu_zfetch.h>
Expand Down Expand Up @@ -65,20 +66,23 @@ typedef struct zfetch_stats {
kstat_named_t zfetchstat_misses;
kstat_named_t zfetchstat_max_streams;
kstat_named_t zfetchstat_io_issued;
kstat_named_t zfetchstat_io_active;
} zfetch_stats_t;

static zfetch_stats_t zfetch_stats = {
{ "hits", KSTAT_DATA_UINT64 },
{ "misses", KSTAT_DATA_UINT64 },
{ "max_streams", KSTAT_DATA_UINT64 },
{ "io_issued", KSTAT_DATA_UINT64 },
{ "io_issued", KSTAT_DATA_UINT64 },
{ "io_active", KSTAT_DATA_UINT64 },
};

struct {
wmsum_t zfetchstat_hits;
wmsum_t zfetchstat_misses;
wmsum_t zfetchstat_max_streams;
wmsum_t zfetchstat_io_issued;
aggsum_t zfetchstat_io_active;
} zfetch_sums;

#define ZFETCHSTAT_BUMP(stat) \
Expand All @@ -104,6 +108,8 @@ zfetch_kstats_update(kstat_t *ksp, int rw)
wmsum_value(&zfetch_sums.zfetchstat_max_streams);
zs->zfetchstat_io_issued.value.ui64 =
wmsum_value(&zfetch_sums.zfetchstat_io_issued);
zs->zfetchstat_io_active.value.ui64 =
aggsum_value(&zfetch_sums.zfetchstat_io_active);
return (0);
}

Expand All @@ -114,6 +120,7 @@ zfetch_init(void)
wmsum_init(&zfetch_sums.zfetchstat_misses, 0);
wmsum_init(&zfetch_sums.zfetchstat_max_streams, 0);
wmsum_init(&zfetch_sums.zfetchstat_io_issued, 0);
aggsum_init(&zfetch_sums.zfetchstat_io_active, 0);

zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
Expand All @@ -138,6 +145,8 @@ zfetch_fini(void)
wmsum_fini(&zfetch_sums.zfetchstat_misses);
wmsum_fini(&zfetch_sums.zfetchstat_max_streams);
wmsum_fini(&zfetch_sums.zfetchstat_io_issued);
ASSERT0(aggsum_value(&zfetch_sums.zfetchstat_io_active));
aggsum_fini(&zfetch_sums.zfetchstat_io_active);
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}

/*
Expand Down Expand Up @@ -294,6 +303,7 @@ dmu_zfetch_done(void *arg, uint64_t level, uint64_t blkid, boolean_t io_issued)
zs->zs_more = B_TRUE;
if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
dmu_zfetch_stream_fini(zs);
aggsum_add(&zfetch_sums.zfetchstat_io_active, -1);
}

/*
Expand Down Expand Up @@ -407,20 +417,28 @@ dmu_zfetch_prepare(zfetch_t *zf, uint64_t blkid, uint64_t nblks,
* Start prefetch from the demand access size (nblks). Double the
* distance every access up to zfetch_min_distance. After that only
* if needed increase the distance by 1/8 up to zfetch_max_distance.
*
* Don't double the distance beyond single block if we have more
* than ~6% of ARC held by active prefetches. It should help with
* getting out of RAM on some badly mispredicted read patterns.
*/
unsigned int nbytes = nblks << zf->zf_dnode->dn_datablkshift;
unsigned int dbs = zf->zf_dnode->dn_datablkshift;
unsigned int nbytes = nblks << dbs;
unsigned int pf_nblks;
if (fetch_data) {
if (unlikely(zs->zs_pf_dist < nbytes))
zs->zs_pf_dist = nbytes;
else if (zs->zs_pf_dist < zfetch_min_distance)
else if (zs->zs_pf_dist < zfetch_min_distance &&
(zs->zs_pf_dist < (1 << dbs) ||
aggsum_compare(&zfetch_sums.zfetchstat_io_active,
arc_c_max >> (4 + dbs)) < 0))
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zs->zs_pf_dist *= 2;
else if (zs->zs_more)
zs->zs_pf_dist += zs->zs_pf_dist / 8;
zs->zs_more = B_FALSE;
if (zs->zs_pf_dist > zfetch_max_distance)
zs->zs_pf_dist = zfetch_max_distance;
pf_nblks = zs->zs_pf_dist >> zf->zf_dnode->dn_datablkshift;
pf_nblks = zs->zs_pf_dist >> dbs;
} else {
pf_nblks = 0;
}
Expand All @@ -439,7 +457,7 @@ dmu_zfetch_prepare(zfetch_t *zf, uint64_t blkid, uint64_t nblks,
zs->zs_ipf_dist *= 2;
if (zs->zs_ipf_dist > zfetch_max_idistance)
zs->zs_ipf_dist = zfetch_max_idistance;
pf_nblks = zs->zs_ipf_dist >> zf->zf_dnode->dn_datablkshift;
pf_nblks = zs->zs_ipf_dist >> dbs;
if (zs->zs_ipf_start < zs->zs_pf_end)
zs->zs_ipf_start = zs->zs_pf_end;
if (zs->zs_ipf_end < zs->zs_pf_end + pf_nblks)
Expand Down Expand Up @@ -510,6 +528,7 @@ dmu_zfetch_run(zstream_t *zs, boolean_t missed, boolean_t have_lock)
dmu_zfetch_stream_fini(zs);
return;
}
aggsum_add(&zfetch_sums.zfetchstat_io_active, issued);

if (!have_lock)
rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);
Expand Down