From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755312AbXIHUVG (ORCPT ); Sat, 8 Sep 2007 16:21:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754615AbXIHUUz (ORCPT ); Sat, 8 Sep 2007 16:20:55 -0400 Received: from mx1.redhat.com ([66.187.233.31]:47039 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754002AbXIHUUy (ORCPT ); Sat, 8 Sep 2007 16:20:54 -0400 Message-ID: <46E30411.3070500@redhat.com> Date: Sat, 08 Sep 2007 16:20:33 -0400 From: Rik van Riel Organization: Red Hat, Inc User-Agent: Thunderbird 1.5.0.7 (X11/20061008) MIME-Version: 1.0 To: Pavel Machek 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 References: <46DF3545.4050604@redhat.com> <20070907122437.GC3901@ucw.cz> In-Reply-To: <20070907122437.GC3901@ucw.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Pavel Machek wrote: > 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. Please read the code this patch applies to. The check I add conditionalizes the individual calls to shrink_zone(), so we do not call shrink_zone() for a zone that has a ton of free pages. We still call shrink_zone() for the other zones. -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic. From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <46E30411.3070500@redhat.com> Date: Sat, 08 Sep 2007 16:20:33 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH] prevent kswapd from freeing excessive amounts of lowmem References: <46DF3545.4050604@redhat.com> <20070907122437.GC3901@ucw.cz> In-Reply-To: <20070907122437.GC3901@ucw.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Pavel Machek Cc: Linux kernel Mailing List , linux-mm@kvack.org, akpm@linux-foundation.org, safari-kernel@safari.iki.fi List-ID: Pavel Machek wrote: > 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. Please read the code this patch applies to. The check I add conditionalizes the individual calls to shrink_zone(), so we do not call shrink_zone() for a zone that has a ton of free pages. We still call shrink_zone() for the other zones. -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic. -- 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-mm.org/ . Don't email: email@kvack.org