Date: Tue, 16 Aug 2016 22:34:16 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: freebsd-fs@freebsd.org Subject: ZFS ARC under memory pressure Message-ID: <20160816193416.GM8192@zxy.spb.ru>
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I see issuses with ZFS ARC inder memory pressure.
ZFS ARC size can be dramaticaly reduced, up to arc_min.
As I see memory pressure event cause call arc_lowmem and set needfree:
arc.c:arc_lowmem
needfree = btoc(arc_c >> arc_shrink_shift);
After this, arc_available_memory return negative vaules (PAGESIZE *
(-needfree)) until needfree is zero. Independent how too much memory
freed. needfree set to 0 in arc_reclaim_thread(), when arc_size <=
arc_c. Until arc_size don't drop below arc_c (arc_c deceased at every
loop interation).
arc_c droped to minimum value if arc_size fast enough droped.
No control current to initial memory allocation.
As result, I can see needless arc reclaim, from 10x to 100x times.
Can some one check me and comment this?
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