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Allow "arc_p" to drop to zero or grow to "arc_c"

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Setting a limit on the minimum value of "arc_p" has been shown to have
detrimental effects on the arc hit rate for certain "metadata" intensive
workloads. Specifically, this has been exhibited with a workload that
constantly dirties new "metadata" but also frequently touches a "small"
amount of mfu data (e.g. mkdir's).

What is seen is that the new anon data throttles the mfu list to a
negligible size (because arc_p > anon + mru in arc_get_data_buf), even
though the mfu ghost list receives a constant stream of hits. To remedy
this, arc_p is now allowed to drop to zero if the algorithm deems it
necessary.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2110
This commit is contained in:
Prakash Surya 2014-01-03 10:20:21 -08:00 committed by Brian Behlendorf
parent 89c8cac493
commit f521ce1b9c
2 changed files with 4 additions and 24 deletions
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11
man/man5/zfs-module-parameters.5
View File

@ -293,17 +293,6 @@ Min life of prefetch block
Default value: \fB100\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

17
module/zfs/arc.c
View File

@ -172,9 +172,6 @@ int arc_evict_iterations = 100;
/* number of seconds before growing cache again */
int zfs_arc_grow_retry = 5;
/* shift of arc_c for calculating both min and max arc_p */
int zfs_arc_p_min_shift = 4;
/* disable anon data aggressively growing arc_p */
int zfs_arc_p_aggressive_disable = 1;
@ -2335,7 +2332,6 @@ void
arc_shrink(uint64_t bytes)
{
if (arc_c > arc_c_min) {
uint64_t arc_p_min;
uint64_t to_free;
to_free = bytes ? bytes : arc_c >> zfs_arc_shrink_shift;
@ -2345,13 +2341,12 @@ arc_shrink(uint64_t bytes)
else
arc_c = arc_c_min;
arc_p_min = (arc_c >> zfs_arc_p_min_shift);
to_free = bytes ? bytes : arc_p >> zfs_arc_shrink_shift;
if (arc_p > arc_p_min + to_free)
if (arc_p > to_free)
atomic_add_64(&arc_p, -to_free);
else
arc_p = arc_p_min;
arc_p = 0;
if (arc_c > arc_size)
arc_c = MAX(arc_size, arc_c_min);
@ -2622,7 +2617,6 @@ static void
arc_adapt(int bytes, arc_state_t *state)
{
int mult;
uint64_t arc_p_min = (arc_c >> zfs_arc_p_min_shift);
if (state == arc_l2c_only)
return;
@ -2641,7 +2635,7 @@ arc_adapt(int bytes, arc_state_t *state)
1 : (arc_mfu_ghost->arcs_size/arc_mru_ghost->arcs_size));
mult = MIN(mult, 10); /* avoid wild arc_p adjustment */
arc_p = MIN(arc_c - arc_p_min, arc_p + bytes * mult);
arc_p = MIN(arc_c, arc_p + bytes * mult);
} else if (state == arc_mfu_ghost) {
uint64_t delta;
@ -2650,7 +2644,7 @@ arc_adapt(int bytes, arc_state_t *state)
mult = MIN(mult, 10);
delta = MIN(bytes * mult, arc_p);
arc_p = MAX(arc_p_min, arc_p - delta);
arc_p = MAX(0, arc_p - delta);
}
ASSERT((int64_t)arc_p >= 0);
@ -5563,9 +5557,6 @@ MODULE_PARM_DESC(zfs_arc_p_aggressive_disable, "disable aggressive arc_p grow");
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");