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Illumos 5034 - ARC's buf_hash_table is too small 

5034 ARC's buf_hash_table is too small

Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Reviewed by: Richard Elling <richard.elling@gmail.com>
Approved by: Gordon Ross <gwr@nexenta.com>

References:
  https://www.illumos.org/issues/5034
  https://github.com/illumos/illumos-gate/commit/63e911b

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2615
This commit is contained in:
Matthew Ahrens 2014-08-20 10:09:40 -07:00 committed by Brian Behlendorf
parent d09a99f96b
commit 49ddb31506
2 changed files with 26 additions and 3 deletions
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16
man/man5/zfs-module-parameters.5
View File

@ -274,6 +274,22 @@ Min time before an active prefetch stream can be reclaimed
Default value: \fB2\fR. Default value: \fB2\fR.
.RE .RE
.sp
.ne 2
.na
\fBzfs_arc_average_blocksize\fR (int)
.ad
.RS 12n
The ARC's buffer hash table is sized based on the assumption of an average
block size of \fBzfs_arc_average_blocksize\fR (default 8K). This works out
to roughly 1MB of hash table per 1GB of physical memory with 8-byte pointers.
For configurations with a known larger average block size this value can be
increased to reduce the memory footprint.
.sp
Default value: \fB8192\fR.
.RE
.sp .sp
.ne 2 .ne 2
.na .na

13
module/zfs/arc.c
View File

@ -193,6 +193,9 @@ int zfs_arc_memory_throttle_disable = 1;
/* disable duplicate buffer eviction */ /* disable duplicate buffer eviction */
int zfs_disable_dup_eviction = 0; int zfs_disable_dup_eviction = 0;
/* average block used to size buf_hash_table */
int zfs_arc_average_blocksize = 8 * 1024; /* 8KB */
/* /*
* If this percent of memory is free, don't throttle. * If this percent of memory is free, don't throttle.
*/ */
@ -1003,10 +1006,11 @@ buf_init(void)
/* /*
* The hash table is big enough to fill all of physical memory * The hash table is big enough to fill all of physical memory
* with an average 64K block size. The table will take up * with an average block size of zfs_arc_average_blocksize (default 8K).
* totalmem*sizeof(void*)/64K (eg. 128KB/GB with 8-byte pointers). * By default, the table will take up
* totalmem * sizeof(void*) / 8K (1MB per GB with 8-byte pointers).
*/ */
while (hsize * 65536 < physmem * PAGESIZE) while (hsize * zfs_arc_average_blocksize < physmem * PAGESIZE)
hsize <<= 1; hsize <<= 1;
retry: retry:
buf_hash_table.ht_mask = hsize - 1; buf_hash_table.ht_mask = hsize - 1;
@ -5657,6 +5661,9 @@ MODULE_PARM_DESC(zfs_arc_shrink_shift, "log2(fraction of arc to reclaim)");
module_param(zfs_disable_dup_eviction, int, 0644); module_param(zfs_disable_dup_eviction, int, 0644);
MODULE_PARM_DESC(zfs_disable_dup_eviction, "disable duplicate buffer eviction"); MODULE_PARM_DESC(zfs_disable_dup_eviction, "disable duplicate buffer eviction");
module_param(zfs_arc_average_blocksize, int, 0444);
MODULE_PARM_DESC(zfs_arc_average_blocksize, "Target average block size");
module_param(zfs_arc_memory_throttle_disable, int, 0644); module_param(zfs_arc_memory_throttle_disable, int, 0644);
MODULE_PARM_DESC(zfs_arc_memory_throttle_disable, "disable memory throttle"); MODULE_PARM_DESC(zfs_arc_memory_throttle_disable, "disable memory throttle");