Date: Wed, 16 May 2001 01:55:13 +0200 From: Roger Larsson <roger.larsson@norran.net> To: Matt Dillon <dillon@earth.backplane.com> Cc: Rik van Riel <riel@conectiva.com.br>, arch@FreeBSD.ORG, linux-mm@kvack.org, sfkaplan@cs.amherst.edu Subject: Re: on load control / process swapping Message-ID: <200105160005.f4G05fe26435@maila.telia.com> In-Reply-To: <200105151724.f4FHOYt54576@earth.backplane.com> References: <Pine.LNX.4.21.0105131417550.5468-100000@imladris.rielhome.conectiva> <3B00CECF.9A3DEEFA@mindspring.com> <200105151724.f4FHOYt54576@earth.backplane.com>
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On Tuesday 15 May 2001 19:24, Matt Dillon wrote: > I implemented a special page-recycling algorithm in 4.1/4.2 (which is > still there in 4.3). Basically it tries predict when it is possible to > throw away pages 'behind' a sequentially accessed file, so as not to > allow that file to blow away your cache. E.G. if you have 128M of ram > and you are sequentially accessing a 200MB file, obviously there is > not much point in trying to cache the data as you read it. > > But being able to predict something like this is extremely difficult. > In fact, nearly impossible. And without being able to make the > prediction accurately you simply cannot determine how much data you > should try to cache before you begin recycling it. I wound up having > to change the algorithm to act more like a heuristic -- it does a rough > prediction but doesn't hold the system to it, then allows the page > priority mechanism to refine the prediction. But it can take several > passes (or non-passes) on the file before the page recycling > stabilizes. > Are the heuristics persistent? Or will the first use after boot use the rough prediction? For how long time will the heuristic stick? Suppose it is suddenly used in a slightly different way. Like two sequential readers instead of one... /RogerL -- Roger Larsson Skellefteċ Sweden To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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