From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 25 May 2000 09:18:49 -0700 (PDT) From: Matthew Dillon Message-Id: <200005251618.JAA82894@apollo.backplane.com> Subject: Re: [RFC] 2.3/4 VM queues idea References: <200005242057.NAA77059@apollo.backplane.com> <20000525115202.A19969@pcep-jamie.cern.ch> Sender: owner-linux-mm@kvack.org Return-Path: To: Jamie Lokier Cc: Rik van Riel , linux-mm@kvack.org List-ID: : :Matthew Dillon wrote: :> Virtual :> page scanning has severe scaleability problems over physical page :> scanning. For example, what happens when you have an oracle database :> running with a hundred independant (non-threaded) processes mapping :> 300MB+ of shared memory? : :Actually you can make this scalable quite easily. I think it's :asymptotically equivalent to physical page scanning. : :First, ensure the async. unmapper can limit the number of mapped :ptes. Method: whenever the number of established ptes increases :above a high water mark (e.g. due to a page fault), invoke the unmapper :synchronously to push the number below a low water mark. (Both marks :can be the same). : :Second, make the scanner scale independently of the virtual addresses :used. Method: store boundary tags in the /unused/ ptes so that :scanning skips unused ptes. Ok, this can have fiddly interactions with :not-present swap entries. : :In this way, the work required to scan _all_ mapped pages can be :strictly bounded. : :cheers, :-- Jamie Yes, but at an unreasonable cost: Artificially limiting the number of discrete processes able to share a given amount of memory. Any reasonable limit would still be an order of magnitude more expensive then a physical page scan. And even with limits you still wind up with extremely non-deterministic scanning. I'm not advocating a physical page scan for the current linux kernel, it just isn't designed for it, but I would argue that doing a physical page scan should be considered after you get past your next release. -Matt Matthew Dillon -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux.eu.org/Linux-MM/