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Enforce ARC meta-data limits

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This change ensures the ARC meta-data limits are enforced.  Without
this enforcement meta-data can grow to consume all of the ARC cache
pushing out data and hurting performance.  The cache is aggressively
reclaimed but this is a soft and not a hard limit.  The cache may
exceed the set limit briefly before being brought under control.

By default 25% of the ARC capacity can be used for meta-data.  This
limit can be tuned by setting the 'zfs_arc_meta_limit' module option.
Once this limit is exceeded meta-data reclaim will occur in 3 percent
chunks, or may be tuned using 'arc_reduce_dnlc_percent'.

Closes #193
This commit is contained in:
Brian Behlendorf 2011-03-30 18:59:17 -07:00
parent 36df284366
commit 6a8f9b6bf0
1 changed files with 15 additions and 2 deletions
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17
module/zfs/arc.c
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@ -180,6 +180,7 @@ unsigned long zfs_arc_meta_limit = 0;
int zfs_arc_grow_retry = 0;
int zfs_arc_shrink_shift = 0;
int zfs_arc_p_min_shift = 0;
int zfs_arc_reduce_dnlc_percent = 0;
/*
* Note that buffers can be in one of 6 states:
@ -2084,14 +2085,16 @@ arc_kmem_reap_now(arc_reclaim_strategy_t strat)
kmem_cache_t *prev_data_cache = NULL;
extern kmem_cache_t *zio_buf_cache[];
extern kmem_cache_t *zio_data_buf_cache[];
#ifdef _KERNEL
if (arc_meta_used >= arc_meta_limit) {
int retry = 0;
while ((arc_meta_used >= arc_meta_limit) && (retry < 10)) {
/*
* We are exceeding our meta-data cache limit.
* Purge some DNLC entries to release holds on meta-data.
*/
dnlc_reduce_cache((void *)(uintptr_t)arc_reduce_dnlc_percent);
retry++;
}
#if defined(__i386)
/*
@ -2157,6 +2160,10 @@ arc_reclaim_thread(void)
arc_no_grow = FALSE;
}
/* Keep meta data usage within limits */
if (arc_meta_used >= arc_meta_limit)
arc_kmem_reap_now(ARC_RECLAIM_CONS);
arc_adjust();
if (arc_eviction_list != NULL)
@ -3583,6 +3590,9 @@ arc_init(void)
if (zfs_arc_p_min_shift > 0)
arc_p_min_shift = zfs_arc_p_min_shift;
if (zfs_arc_reduce_dnlc_percent > 0)
arc_reduce_dnlc_percent = zfs_arc_reduce_dnlc_percent;
/* if kmem_flags are set, lets try to use less memory */
if (kmem_debugging())
arc_c = arc_c / 2;
@ -4765,4 +4775,7 @@ MODULE_PARM_DESC(zfs_arc_max, "Maximum arc size");
module_param(zfs_arc_meta_limit, ulong, 0644);
MODULE_PARM_DESC(zfs_arc_meta_limit, "Meta limit for arc size");
module_param(arc_reduce_dnlc_percent, uint, 0644);
MODULE_PARM_DESC(arc_reduce_dnlc_percent, "Meta reclaim percentage");
#endif