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Date: Fri, 10 Sep 2010 16:24:00 +0800 From: Dave Young <hidave.darkstar@...il.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Minchan Kim <minchan.kim@...il.com>, Johannes Weiner <hannes@...xchg.org>, linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Rik van Riel <riel@...hat.com>, "Rafael J. Wysocki" <rjw@...k.pl>, "M. Vefa Bicakci" <bicave@...eronline.com>, stable@...nel.org Subject: Re: [PATCH] vmscan: check all_unreclaimable in direct reclaim path On Thu, Sep 9, 2010 at 6:19 AM, Andrew Morton <akpm@...ux-foundation.org> wrote: > On Thu, 9 Sep 2010 00:45:27 +0900 > Minchan Kim <minchan.kim@...il.com> wrote: > >> +static inline bool zone_reclaimable(struct zone *zone) >> +{ >> + return zone->pages_scanned < zone_reclaimable_pages(zone) * 6; >> +} >> + >> +static inline bool all_unreclaimable(struct zonelist *zonelist, >> + struct scan_control *sc) >> +{ >> + struct zoneref *z; >> + struct zone *zone; >> + bool all_unreclaimable = true; >> + >> + if (!scanning_global_lru(sc)) >> + return false; >> + >> + for_each_zone_zonelist_nodemask(zone, z, zonelist, >> + gfp_zone(sc->gfp_mask), sc->nodemask) { >> + if (!populated_zone(zone)) >> + continue; >> + if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) >> + continue; >> + if (zone_reclaimable(zone)) { >> + all_unreclaimable = false; >> + break; >> + } >> + } >> + >> return all_unreclaimable; >> } > > Could we have some comments over these functions please? Why they > exist, what problem they solve, how they solve them, etc. Stuff which > will be needed for maintaining this code three years from now. > > We may as well remove the `inline's too. gcc will tkae care of that. > >> - if (nr_slab == 0 && >> - zone->pages_scanned >= (zone_reclaimable_pages(zone) * 6)) >> + if (nr_slab == 0 && !zone_reclaimable(zone)) > > Extra marks for working out and documenting how we decided on the value > of "6". Sigh. It's hopefully in the git record somewhere. Here it is (necessary to add additional comment?): commit 4ff1ffb4870b007b86f21e5f27eeb11498c4c077 Author: Nick Piggin <npiggin@...e.de> Date: Mon Sep 25 23:31:28 2006 -0700 [PATCH] oom: reclaim_mapped on oom Potentially it takes several scans of the lru lists before we can even start reclaiming pages. mapped pages, with young ptes can take 2 passes on the active list + one on the inactive list. But reclaim_mapped may not always kick in instantly, so it could take even more than that. Raise the threshold for marking a zone as all_unreclaimable from a factor of 4 time the pages in the zone to 6. Introduce a mechanism to force reclaim_mapped if we've reached a factor 3 and still haven't made progress. Previously, a customer doing stress testing was able to easily OOM the box after using only a small fraction of its swap (~100MB). After the patches, it would only OOM after having used up all swap (~800MB). > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@...ck.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a> > > -- Regards dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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