From 728d6ae91e5381cda813672c9e9f66a269f58368 Mon Sep 17 00:00:00 2001
From: Brian Behlendorf <behlendorf1@llnl.gov>
Date: Fri, 26 Jun 2015 15:59:23 -0700
Subject: [PATCH] Reinstate zfs_arc_p_min_shift
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
---
man/man5/zfs-module-parameters.5 | 12 ++++++++++++
module/zfs/arc.c | 16 ++++++++++++++--
2 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index 0444d9050c..5b6eb7afd9 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -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
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index aaf2682642..2661bc8a78 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -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");