Date: Thu, 18 Aug 2016 17:54:55 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Matthias Gamsjager <mgamsjager@gmail.com>, freebsd-fs@freebsd.org Subject: Re: ZFS ARC under memory pressure Message-ID: <20160818145455.GA48739@zxy.spb.ru> In-Reply-To: <CA%2BD9Qhv0MW6mkEWDhGuB-S7W_6oxV5bKJ6GGpSzdqQYnNPeyhA@mail.gmail.com> References: <20160816193416.GM8192@zxy.spb.ru> <CA%2BD9Qhv0MW6mkEWDhGuB-S7W_6oxV5bKJ6GGpSzdqQYnNPeyhA@mail.gmail.com>
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On Wed, Aug 17, 2016 at 09:18:20AM +0200, Matthias Gamsjager wrote: > On 16 August 2016 at 21:34, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote: > > > 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? > > _______________________________________________ > > > > > What version are you on? stable/10, same code in stable/11/9 and current/12 -- Slawa Olhovchenkov
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