From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423102AbWJYILu (ORCPT ); Wed, 25 Oct 2006 04:11:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423106AbWJYILu (ORCPT ); Wed, 25 Oct 2006 04:11:50 -0400 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:14734 "EHLO amd.ucw.cz") by vger.kernel.org with ESMTP id S1423102AbWJYILt (ORCPT ); Wed, 25 Oct 2006 04:11:49 -0400 Date: Wed, 25 Oct 2006 10:11:35 +0200 From: Pavel Machek To: Nigel Cunningham Cc: "Rafael J. Wysocki" , Andrew Morton , LKML Subject: Re: [PATCH] Use extents for recording what swap is allocated. Message-ID: <20061025081135.GM5851@elf.ucw.cz> References: <1161576857.3466.9.camel@nigel.suspend2.net> <200610242208.34426.rjw@sisk.pl> <20061024213402.GC5662@elf.ucw.cz> <1161728153.22729.22.camel@nigel.suspend2.net> <20061024221950.GB5851@elf.ucw.cz> <1161729027.22729.37.camel@nigel.suspend2.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1161729027.22729.37.camel@nigel.suspend2.net> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.11+cvs20060126 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > > > That's right. In using this, we're relying on the fact that the swap > > > allocator tries to act sensibly. I've only seen worse case performance > > > when a user had two swap devices with the same priority (striped), but > > > that was a bug. :) > > > > Ok, but if the allocator somehow manages to stripe between two swap > > devices, what happens? > > > > IIRC original code was something like .1% overhead (8bytes per 4K, or > > something?), bitmaps should be even better. If it is 1% in worst case, > > that's probably okay, but it would be bad if it had overhead bigger > > than 10times original code (worst case). > > With the code I have in Suspend2 (which is what I'm working towards), > the value includes the swap_type, so there's no overlap. Assuming the > swap allocator does it's normal thing and swap allocated is contiguous, > you'll probably end up with two extents: one containing the swap > allocated on the first device, and the other containing the swap > allocated on the second device. So (with the current version), striping > would use 6 * sizeof(unsigned long) instead of 3 * sizeof(unsigned > long). And now, can you do same computation assuming the swap allocator goes completely crazy, and free space is in 1-page chunks? In particular, how much swap space can we have before we run out of low memory? What is the overhead compared to bitmaps? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html