Date: Sun, 25 Jul 2010 23:43:08 +0300 From: Andriy Gapon <avg@freebsd.org> To: RW <rwmaillists@googlemail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: pageout question Message-ID: <4C4CA1DC.2050902@freebsd.org> In-Reply-To: <20100725212849.1e07f40c@gumby.homeunix.com> References: <4C4B4BAB.3000005@freebsd.org> <20100725003144.3cfead39@gumby.homeunix.com> <4C4C0CD9.6000002@freebsd.org> <20100725144141.6f1f33cc@gumby.homeunix.com> <4C4C47FD.6080802@freebsd.org> <20100725212849.1e07f40c@gumby.homeunix.com>
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on 25/07/2010 23:28 RW said the following: > On Sun, 25 Jul 2010 17:19:41 +0300 > Andriy Gapon <avg@freebsd.org> wrote: > >> on 25/07/2010 16:41 RW said the following: > >>> In FreeBSD the inactive queue contains disk cache pages which >>> normally provide most of the clean pages needed. In addition pages >>> are dribbled out to swap, and the resulting clean pages are placed >>> at the back of the inactive queue to make another pass. >> Well, "normally" and "most" are not quite quantitative. >> Personally, I do not see any guarantees that inactive queue would >> contain enough clean pages to reach paging target on a single pass. > > I didn't say it say it was guaranteed. I just think the scenario where > a first pass ends up between the watermarks is rare. And when it > happens I don't see a compelling reason to do extra paging to reach an > arbitrary target. Well, it seems neither I nor you have data to show whether it's rare or not (and it would greatly depend on workload too). As to "arbitrary target" - well, that's the whole point of hysteresis-like behavior. We start paging also at an "arbitrary" point. -- Andriy Gapon
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