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OpenZFS 9188 - increase size of dbuf cache to reduce indirect block decompression #7273

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Mar 13, 2018
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OpenZFS 9188 - increase size of dbuf cache to reduce indirect block decompression #7273

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51 changes: 51 additions & 0 deletions man/man5/zfs-module-parameters.5
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,57 @@ Description of the different parameters to the ZFS module.
.sp
.LP

.sp
.ne 2
.na
\fBdbuf_cache_max_bytes\fR (ulong)
.ad
.RS 12n
Maximum size in bytes of the dbuf cache. When \fB0\fR this value will default
to \fB1/2^dbuf_cache_shift\fR (1/32) of the target ARC size, otherwise the
provided value in bytes will be used. The behavior of the dbuf cache and its
associated settings can be observed via the \fB/proc/spl/kstat/zfs/dbufstats\fR
kstat.
.sp
Default value: \fB0\fR.
.RE

.sp
.ne 2
.na
\fBdbuf_cache_hiwater_pct\fR (uint)
.ad
.RS 12n
The percentage over \fBdbuf_cache_max_bytes\fR when dbufs must be evicted
directly.
.sp
Default value: \fB10\fR%.
.RE

.sp
.ne 2
.na
\fBdbuf_cache_lowater_pct\fR (uint)
.ad
.RS 12n
The percentage below \fBdbuf_cache_max_bytes\fR when the evict thread stops
evicting dbufs.
.sp
Default value: \fB10\fR%.
.RE

.sp
.ne 2
.na
\fBdbuf_cache_shift\fR (int)
.ad
.RS 12n
Set the size of the dbuf cache, \fBdbuf_cache_max_bytes\fR, to a log2 fraction
of the target arc size.
.sp
Default value: \fB5\fR.
.RE

.sp
.ne 2
.na
Expand Down
26 changes: 15 additions & 11 deletions module/zfs/dbuf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -186,10 +186,10 @@ static boolean_t dbuf_evict_thread_exit;
*/
static multilist_t *dbuf_cache;
static refcount_t dbuf_cache_size;
unsigned long dbuf_cache_max_bytes = 100 * 1024 * 1024;
unsigned long dbuf_cache_max_bytes = 0;

/* Cap the size of the dbuf cache to log2 fraction of arc size. */
int dbuf_cache_max_shift = 5;
/* Set the default size of the dbuf cache to log2 fraction of arc size. */
int dbuf_cache_shift = 5;

/*
* The dbuf cache uses a three-stage eviction policy:
Expand Down Expand Up @@ -561,7 +561,7 @@ static inline unsigned long
dbuf_cache_target_bytes(void)
{
return MIN(dbuf_cache_max_bytes,
arc_target_bytes() >> dbuf_cache_max_shift);
arc_target_bytes() >> dbuf_cache_shift);
}

static inline uint64_t
Expand Down Expand Up @@ -787,11 +787,15 @@ dbuf_init(void)
dbuf_stats_init(h);

/*
* Setup the parameters for the dbuf cache. We cap the size of the
* dbuf cache to 1/32nd (default) of the size of the ARC.
* Setup the parameters for the dbuf cache. We set the size of the
* dbuf cache to 1/32nd (default) of the target size of the ARC. If
* the value has been specified as a module option and it's not
* greater than the target size of the ARC, then we honor that value.
*/
dbuf_cache_max_bytes = MIN(dbuf_cache_max_bytes,
arc_target_bytes() >> dbuf_cache_max_shift);
if (dbuf_cache_max_bytes == 0 ||
dbuf_cache_max_bytes >= arc_target_bytes()) {
dbuf_cache_max_bytes = arc_target_bytes() >> dbuf_cache_shift;
}

/*
* All entries are queued via taskq_dispatch_ent(), so min/maxalloc
Expand Down Expand Up @@ -4216,8 +4220,8 @@ MODULE_PARM_DESC(dbuf_cache_lowater_pct,
"Percentage below dbuf_cache_max_bytes when the evict thread stops "
"evicting dbufs.");

module_param(dbuf_cache_max_shift, int, 0644);
MODULE_PARM_DESC(dbuf_cache_max_shift,
"Cap the size of the dbuf cache to a log2 fraction of arc size.");
module_param(dbuf_cache_shift, int, 0644);
MODULE_PARM_DESC(dbuf_cache_shift,
"Set the size of the dbuf cache to a log2 fraction of arc size.");
/* END CSTYLED */
#endif