From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 20 May 2002 20:15:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 20 May 2002 20:15:31 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.101]:41164 "EHLO e1.ny.us.ibm.com") by vger.kernel.org with ESMTP id ; Mon, 20 May 2002 20:15:30 -0400 Date: Mon, 20 May 2002 17:14:24 -0700 From: "Martin J. Bligh" To: Andrea Arcangeli , Rik van Riel cc: Andrew Morton , Martin Schwidefsky , linux-kernel@vger.kernel.org, Alan Cox Subject: Re: Bug with shared memory. Message-ID: <262840000.1021940064@flay> In-Reply-To: <20020520234622.GL21806@dualathlon.random> X-Mailer: Mulberry/2.1.2 (Linux/x86) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > For the memclass_related_bhs() fix in -aa, that's in the testing TODO > list of Martin (on the multi giga machines), he also nicely proposed to > compare it to the other throw-away-all-bh-regardless patch from Andrew > (that I actually didn't seen floating around yet but it's clear how it > works, it's a subset of memclass_related_bhs). However the right way to > test the memclass_related_bhs vs throw-away-all-bh, is to run a rewrite > test that fits in cache, so write,fsync,write,fsync,write,fsync. specweb > or any other read-only test will obviously perform exactly the same both > ways (actually theoretically a bit cpu-faster in throw-away-all-bh > because it doesn't check the bh list). The only thing that worries me in theory about your approach for this Andrea is fragmentation - if we try to shrink only when we're low on memory, isn't there a danger that one buffer_head per page of slab cache will be in use, and thus no pages are freeable (obviously this is extreme, but I can certainly see a situation with lots of partially used pages)? With Andrew's approach, keeping things freed as we go, we should reuse the partially allocated slab pages, which would seem (to me) to result in less fragmentation? Thanks, M.