path: root/mm/vmscan.c
diff options
authorMel Gorman <mgorman@suse.de>2012-01-12 17:19:45 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-12 20:13:09 -0800
commitfe4b1b244bdb96136855f2c694071cb09d140766 (patch)
treec1fafe7ef5b5bd7c77ae981b47fa82916e0436eb /mm/vmscan.c
parenta6bc32b899223a877f595ef9ddc1e89ead5072b8 (diff)
mm: vmscan: when reclaiming for compaction, ensure there are sufficient free pages available
In commit e0887c19 ("vmscan: limit direct reclaim for higher order allocations"), Rik noted that reclaim was too aggressive when THP was enabled. In his initial patch he used the number of free pages to decide if reclaim should abort for compaction. My feedback was that reclaim and compaction should be using the same logic when deciding if reclaim should be aborted. Unfortunately, this had the effect of reducing THP success rates when the workload included something like streaming reads that continually allocated pages. The window during which compaction could run and return a THP was too small. This patch combines Rik's two patches together. compaction_suitable() is still used to decide if reclaim should be aborted to allow compaction is used. However, it will also ensure that there is a reasonable buffer of free pages available. This improves upon the THP allocation success rates but bounds the number of pages that are freed for compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel<riel@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: Dave Jones <davej@redhat.com> Cc: Jan Kara <jack@suse.cz> Cc: Andy Isaacson <adi@hexapodia.org> Cc: Nai Xia <nai.xia@gmail.com> Cc: Johannes Weiner <jweiner@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
1 files changed, 39 insertions, 5 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index efbcab1c8f5..3b8ede88239 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2163,6 +2163,42 @@ static void shrink_zone(int priority, struct zone *zone,
} while (memcg);
+/* Returns true if compaction should go ahead for a high-order request */
+static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
+ unsigned long balance_gap, watermark;
+ bool watermark_ok;
+ /* Do not consider compaction for orders reclaim is meant to satisfy */
+ if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
+ return false;
+ /*
+ * Compaction takes time to run and there are potentially other
+ * callers using the pages just freed. Continue reclaiming until
+ * there is a buffer of free pages available to give compaction
+ * a reasonable chance of completing and allocating the page
+ */
+ balance_gap = min(low_wmark_pages(zone),
+ (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
+ watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
+ watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
+ /*
+ * If compaction is deferred, reclaim up to a point where
+ * compaction will have a chance of success when re-enabled
+ */
+ if (compaction_deferred(zone))
+ return watermark_ok;
+ /* If compaction is not ready to start, keep reclaiming */
+ if (!compaction_suitable(zone, sc->order))
+ return false;
+ return watermark_ok;
* This is the direct reclaim path, for page-allocating processes. We only
* try to reclaim pages from zones which will satisfy the caller's allocation
@@ -2180,8 +2216,8 @@ static void shrink_zone(int priority, struct zone *zone,
* scan then give up on it.
* This function returns true if a zone is being reclaimed for a costly
- * high-order allocation and compaction is either ready to begin or deferred.
- * This indicates to the caller that it should retry the allocation or fail.
+ * high-order allocation and compaction is ready to begin. This indicates to
+ * the caller that it should retry the allocation or fail.
static bool shrink_zones(int priority, struct zonelist *zonelist,
struct scan_control *sc)
@@ -2215,9 +2251,7 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
* noticable problem, like transparent huge page
* allocations.
- if (sc->order > PAGE_ALLOC_COSTLY_ORDER &&
- (compaction_suitable(zone, sc->order) ||
- compaction_deferred(zone))) {
+ if (compaction_ready(zone, sc)) {
should_abort_reclaim = true;