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Increase default arc_c_min

Increase the default arc_c_min value to which whichever is larger,
either 32M or 1/32 of total system memory.  This is advantageous for
systems with more than 1G of memory where performance issues may
occur when the ARC is allowed to collapse below a minimum size.
At the same time we want to use the bare minimum value which is
still functional so the filesystem can be used in very low memory
environments.

Reviewed-by: Tim Chase <tim@chase2k.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #6659
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behlendorf authored and tonyhutter committed Sep 20, 2017
1 parent c474f5e commit 266b181e7594592e6db63b5e22584373585922ef
Showing with 4 additions and 3 deletions.
  1. +4 −3 module/zfs/arc.c
@@ -6508,16 +6508,17 @@ arc_init(void)
/* Set max to 1/2 of all memory */
arc_c_max = allmem / 2;

#ifdef _KERNEL
/* Set min cache to 1/32 of all memory, or 32MB, whichever is more */
arc_c_min = MAX(allmem / 32, 2ULL << SPA_MAXBLOCKSHIFT);
#else
/*
* In userland, there's only the memory pressure that we artificially
* create (see arc_available_memory()). Don't let arc_c get too
* small, because it can cause transactions to be larger than
* arc_c, causing arc_tempreserve_space() to fail.
*/
#ifndef _KERNEL
arc_c_min = MAX(arc_c_max / 2, 2ULL << SPA_MAXBLOCKSHIFT);
#else
arc_c_min = 2ULL << SPA_MAXBLOCKSHIFT;
#endif

arc_c = arc_c_max;

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