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Reinstate zfs_arc_p_min_shift

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Commit f521ce1 removed the minimum value for "arc_p" allowing it to
drop to zero or grow to "arc_c".  This was done to improve specific
workload which constantly dirties new "metadata" but also frequently
touches a "small" amount of mfu data (e.g. mkdir's).

This change may still be desirable but it needs to be re-investigated.
in the context of the recent ARC changes from upstream.  Therefore
this code is being restored to facilitate benchmarking.  By setting
"zfs_arc_p_min_shift=64" we easily compare the performance.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #3533
This commit is contained in:
Brian Behlendorf 2015-06-26 15:59:23 -07:00
parent 36da08ef9b
commit 728d6ae91e
2 changed files with 26 additions and 2 deletions
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12
man/man5/zfs-module-parameters.5
View File

@ -521,6 +521,18 @@ the reclaim thread catches up and the overflow condition no longer exists.
Default value: \fB8\fR.
.RE
.sp
.ne 2
.na
\fBzfs_arc_p_min_shift\fR (int)
.ad
.RS 12n
arc_c shift to calc min/max arc_p
.sp
Default value: \fB4\fR.
.RE
.sp
.ne 2
.na

16
module/zfs/arc.c
View File

@ -188,6 +188,9 @@ static int arc_grow_retry = 5;
/* shift of arc_c for calculating overflow limit in arc_get_data_buf */
int zfs_arc_overflow_shift = 8;
/* shift of arc_c for calculating both min and max arc_p */
static int arc_p_min_shift = 4;
/* log2(fraction of arc to reclaim) */
static int arc_shrink_shift = 7;
@ -230,6 +233,7 @@ unsigned long zfs_arc_meta_limit = 0;
unsigned long zfs_arc_meta_min = 0;
int zfs_arc_grow_retry = 0;
int zfs_arc_shrink_shift = 0;
int zfs_arc_p_min_shift = 0;
int zfs_disable_dup_eviction = 0;
int zfs_arc_average_blocksize = 8 * 1024; /* 8KB */
@ -3718,6 +3722,7 @@ static void
arc_adapt(int bytes, arc_state_t *state)
{
int mult;
uint64_t arc_p_min = (arc_c >> arc_p_min_shift);
int64_t mrug_size = refcount_count(&arc_mru_ghost->arcs_size);
int64_t mfug_size = refcount_count(&arc_mfu_ghost->arcs_size);
@ -3738,7 +3743,7 @@ arc_adapt(int bytes, arc_state_t *state)
if (!zfs_arc_p_dampener_disable)
mult = MIN(mult, 10); /* avoid wild arc_p adjustment */
arc_p = MIN(arc_c, arc_p + bytes * mult);
arc_p = MIN(arc_c - arc_p_min, arc_p + bytes * mult);
} else if (state == arc_mfu_ghost) {
uint64_t delta;
@ -3747,7 +3752,7 @@ arc_adapt(int bytes, arc_state_t *state)
mult = MIN(mult, 10);
delta = MIN(bytes * mult, arc_p);
arc_p = MAX(0, arc_p - delta);
arc_p = MAX(arc_p_min, arc_p - delta);
}
ASSERT((int64_t)arc_p >= 0);
@ -5265,6 +5270,10 @@ arc_tuning_update(void)
arc_no_grow_shift = MIN(arc_no_grow_shift, arc_shrink_shift -1);
}
/* Valid range: 1 - N */
if (zfs_arc_p_min_shift)
arc_p_min_shift = zfs_arc_p_min_shift;
/* Valid range: 1 - N ticks */
if (zfs_arc_min_prefetch_lifespan)
arc_min_prefetch_lifespan = zfs_arc_min_prefetch_lifespan;
@ -6996,6 +7005,9 @@ MODULE_PARM_DESC(zfs_arc_p_dampener_disable, "disable arc_p adapt dampener");
module_param(zfs_arc_shrink_shift, int, 0644);
MODULE_PARM_DESC(zfs_arc_shrink_shift, "log2(fraction of arc to reclaim)");
module_param(zfs_arc_p_min_shift, int, 0644);
MODULE_PARM_DESC(zfs_arc_p_min_shift, "arc_c shift to calc min/max arc_p");
module_param(zfs_disable_dup_eviction, int, 0644);
MODULE_PARM_DESC(zfs_disable_dup_eviction, "disable duplicate buffer eviction");