Re: [PATCH v2 -mm] limit direct reclaim for higher order allocations
From: Mel Gorman <mgorman@suse.de>
Date: 2011-09-28 10:02:21
Also in:
lkml
Subsystem:
memory management, memory management - mglru (multi-gen lru), memory management - reclaim, the rest · Maintainers:
Andrew Morton, Johannes Weiner, Linus Torvalds
On Tue, Sep 27, 2011 at 10:52:46AM -0400, Rik van Riel wrote:
When suffering from memory fragmentation due to unfreeable pages, THP page faults will repeatedly try to compact memory. Due to the unfreeable pages, compaction fails. Needless to say, at that point page reclaim also fails to create free contiguous 2MB areas. However, that doesn't stop the current code from trying, over and over again, and freeing a minimum of 4MB (2UL << sc->order pages) at every single invocation. This resulted in my 12GB system having 2-3GB free memory, a corresponding amount of used swap and very sluggish response times. This can be avoided by having the direct reclaim code not reclaim from zones that already have plenty of free memory available for compaction. If compaction still fails due to unmovable memory, doing additional reclaim will only hurt the system, not help. Signed-off-by: Rik van Riel <redacted>
Because this patch improves things; Acked-by: Mel Gorman <mgorman@suse.de> That said, shrink_zones potentially returns having scanning and reclaimed 0 pages. We still fall through to shrink_slab and because we are reclaiming 0 pages, we loop over all priorities in do_try_to_free_pages() and potentially even call wait_iff_congested. I think this patch would be better if shrink_zones() returned true if we did not reclaim because compaction was ready and returned early from shrink_zones.
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 117eb4d..ead9c94 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c@@ -2061,14 +2061,19 @@ restart: * * If a zone is deemed to be full of pinned pages then just give it a light * scan then give up on it. + * + * This function returns true if a zone is being reclaimed for a high-order + * allocation that will use compaction and compaction is ready to begin. This + * indicates to the caller that further reclaim is unnecessary. */ -static void shrink_zones(int priority, struct zonelist *zonelist, +static bool shrink_zones(int priority, struct zonelist *zonelist, struct scan_control *sc) { struct zoneref *z; struct zone *zone; unsigned long nr_soft_reclaimed; unsigned long nr_soft_scanned; + bool abort_reclaim_compaction = false; for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -2090,8 +2095,10 @@ static void shrink_zones(int priority, struct zonelist *zonelist, */ if (sc->order > PAGE_ALLOC_COSTLY_ORDER && (compaction_suitable(zone, sc->order) || - compaction_deferred(zone))) + compaction_deferred(zone))) { + abort_reclaim_compaction = true; continue; + } } /* * This steals pages from memory cgroups over softlimit
@@ -2110,6 +2117,8 @@ static void shrink_zones(int priority, struct zonelist *zonelist, shrink_zone(priority, zone, sc); } + + return abort_reclaim_compaction; } static bool zone_reclaimable(struct zone *zone)
@@ -2174,7 +2183,8 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, sc->nr_scanned = 0; if (!priority) disable_swap_token(sc->mem_cgroup); - shrink_zones(priority, zonelist, sc); + if (shrink_zones(priority, zonelist, sc)) + break; /* * Don't shrink slabs when reclaiming memory from * over limit cgroups --
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