From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from haymarket.ed.ac.uk (haymarket.ed.ac.uk [129.215.128.53]) by kvack.org (8.8.7/8.8.7) with ESMTP id OAA07476 for ; Thu, 2 Apr 1998 14:23:24 -0500 Date: Wed, 1 Apr 1998 21:28:49 +0100 Message-Id: <199804012028.VAA04493@dax.dcs.ed.ac.uk> From: "Stephen C. Tweedie" MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Subject: Re: new allocation algorithm In-Reply-To: References: Sender: owner-linux-mm@kvack.org To: Linus Torvalds Cc: Rik van Riel , "Stephen C. Tweedie" , linux-mm List-ID: Hi, On Fri, 27 Mar 1998 09:30:40 -0800 (PST), Linus Torvalds said: > The current scheme is fairly efficient and extremely stable, and gives > good behaviour for the cases we _really_ care about (pageorders 0, 1 and > to some degree 2). It comes reasonably close to working for the higher > orders too, but they really aren't as critical.. Sorry to put a spanner in the works at this stage, but there's something we haven't really considered yet in the page balancing. The aim I'm currently working towards is to eliminate free memory as much as possible, by replacing "free" space with reserved, lazy-reclaimed cache memory. We ought to be able to maintain 5-10% memory in this form with much less performance impact than we would have if that memory was truly free, but the downside is that this nearly-free memory is not on our free page lists and therefore we have no simple way of assessing the fragmentation of the lazy-reclaimable pages. Now, this is both a blessing and a curse. The positive side is that we can do what to some extent happens today, and keep as much memory as possible on the lazy list in the blind hope that we will be able to find free higher order pages when we need them by returning lazy pages to the free list one by one. The drawback is that we don't have an easy way of suspending kswapd when we get enough free higher order pages. This is just an observation --- we cannot tune this stuff until it is stable enough to integrate, but the impact on our free space heuristics may be worth thinking about now. --Stephen