From owner-freebsd-hackers@FreeBSD.ORG Sun Jul 25 20:43:13 2010 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id DE979106564A for ; Sun, 25 Jul 2010 20:43:13 +0000 (UTC) (envelope-from avg@freebsd.org) Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140]) by mx1.freebsd.org (Postfix) with ESMTP id 4F1038FC0A for ; Sun, 25 Jul 2010 20:43:12 +0000 (UTC) Received: from porto.topspin.kiev.ua (porto-e.starpoint.kiev.ua [212.40.38.100]) by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id XAA08883; Sun, 25 Jul 2010 23:43:10 +0300 (EEST) (envelope-from avg@freebsd.org) Received: from localhost.topspin.kiev.ua ([127.0.0.1]) by porto.topspin.kiev.ua with esmtp (Exim 4.34 (FreeBSD)) id 1Od82P-000Day-NR; Sun, 25 Jul 2010 23:43:09 +0300 Message-ID: <4C4CA1DC.2050902@freebsd.org> Date: Sun, 25 Jul 2010 23:43:08 +0300 From: Andriy Gapon User-Agent: Thunderbird 2.0.0.24 (X11/20100603) MIME-Version: 1.0 To: RW 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> In-Reply-To: <20100725212849.1e07f40c@gumby.homeunix.com> X-Enigmail-Version: 0.96.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: freebsd-hackers@freebsd.org Subject: Re: pageout question X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 25 Jul 2010 20:43:13 -0000 on 25/07/2010 23:28 RW said the following: > On Sun, 25 Jul 2010 17:19:41 +0300 > Andriy Gapon 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