From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753969AbXIHQVa (ORCPT ); Sat, 8 Sep 2007 12:21:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753317AbXIHQVX (ORCPT ); Sat, 8 Sep 2007 12:21:23 -0400 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:1593 "EHLO spitz.ucw.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753295AbXIHQVW (ORCPT ); Sat, 8 Sep 2007 12:21:22 -0400 Date: Fri, 7 Sep 2007 12:24:37 +0000 From: Pavel Machek To: Rik van Riel Cc: Linux kernel Mailing List , linux-mm@kvack.org, akpm@linux-foundation.org, safari-kernel@safari.iki.fi Subject: Re: [PATCH] prevent kswapd from freeing excessive amounts of lowmem Message-ID: <20070907122437.GC3901@ucw.cz> References: <46DF3545.4050604@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46DF3545.4050604@redhat.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > The current VM can get itself into trouble fairly easily > on systems > with a small ZONE_HIGHMEM, which is common on i686 > computers with > 1GB of memory. > > On one side, page_alloc() will allocate down to > zone->pages_low, > while on the other side, kswapd() and balance_pgdat() > will try > to free memory from every zone, until every zone has > more free > pages than zone->pages_high. > > Highmem can be filled up to zone->pages_low with page > tables, > ramfs, vmalloc allocations and other unswappable things > quite > easily and without many bad side effects, since we still > have > a huge ZONE_NORMAL to do future allocations from. > > However, as long as the number of free pages in the > highmem > zone is below zone->pages_high, kswapd will continue > swapping > things out from ZONE_NORMAL, too! > > Sami Farin managed to get his system into a stage where > kswapd > had freed about 700MB of low memory and was still "going > strong". > > The attached patch will make kswapd stop paging out data > from > zones when there is more than enough memory free. We do > go above > zone->pages_high in order to keep pressure between zones > equal > in normal circumstances, but the patch should prevent > the kind > of excesses that made Sami's computer totally unusable. > > Please merge this into -mm. > > Signed-off-by: Rik van Riel > --- linux-2.6.22.noarch/mm/vmscan.c.excessive 2007-09-05 12:19:49.000000000 -0400 > +++ linux-2.6.22.noarch/mm/vmscan.c 2007-09-05 12:21:40.000000000 -0400 > @@ -1371,7 +1371,13 @@ loop_again: > temp_priority[i] = priority; > sc.nr_scanned = 0; > note_zone_scanning_priority(zone, priority); > - nr_reclaimed += shrink_zone(priority, zone, &sc); > + /* > + * We put equal pressure on every zone, unless one > + * zone has way too many pages free already. > + */ That does not seem right. Having empty HIGHMEM and full LOWMEM would be very bad, right? We may stop freeing when there's enough LOWMEM free, but not if there's only HIGHMEM free. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html