Date: Sat, 7 Sep 2019 10:43:23 -0400 From: Mark Johnston <markj@freebsd.org> To: Andriy Gapon <avg@freebsd.org> Cc: Slawa Olhovchenkov <slw@zxy.spb.ru>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r351673 - in head: lib/libmemstat share/man/man9 sys/cddl/compat/opensolaris/kern sys/kern sys/vm Message-ID: <20190907144323.GA6523@spy> In-Reply-To: <8b049a33-e844-1a47-2be1-c267946b8f95@FreeBSD.org> References: <201909012222.x81MMh0F022462@repo.freebsd.org> <79c74018-1329-ee69-3480-e2f99821fa93@FreeBSD.org> <20190903161427.GA38096@zxy.spb.ru> <20190903220106.GB26733@raichu> <8b049a33-e844-1a47-2be1-c267946b8f95@FreeBSD.org>
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On Wed, Sep 04, 2019 at 09:27:00AM +0300, Andriy Gapon wrote: > On 04/09/2019 01:01, Mark Johnston wrote: > > Some of the vm_lowmem eventhandlers probably shouldn't be called each > > time the page daemon scans the inactive queue (every 0.1s under memory > > pressure). ufsdirhash_lowmem and mb_reclaim in particular don't seem > > like they need to be invoked very frequently. We could easily define > > multiple eventhandlers to differentiate between these cases, though. > > My proposal is to run uma_reclaim(UMA_RECLAIM_TRIM) before invoking vm_lowmem. > If that reclaims "enough" memory, then do not call vm_lowmem at all. > > Oh, and I have a related question. > Say, a zone has X items in use and Y items in cache. > After running vm_lowmem the composition changes to X - C and Y + C respectively. > Then we run uma_reclaim(UMA_RECLAIM_TRIM). > Question: is that guaranteed to free at least C items? No. The estimation cannot distinguish between items that were freed as a result of a lowmem request vs. those that were freed as a regular operation. As a result it considers the extra C items as part of the cache's working size. > I am thinking about a possibility that the zone's workset size is estimated to > be at least X (and maybe even more than X + Y). In that case UMA_RECLAIM_TRIM > won't free those C items, they will stay in the cache. So, it seems like > releasing them was in vain, at least for the immediate reclaim. This is true. Of course, the items may eventually become reclaimable as the estimate decays.home | help
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