Hi!

On 15.10.2012 13:09, Mel Gorman wrote:

On Mon, Oct 15, 2012 at 11:54:13AM +0200, Jiri Slaby wrote:

quoted

On 10/12/2012 03:57 PM, Mel Gorman wrote:

quoted

mm: vmscan: scale number of pages reclaimed by reclaim/compaction only in direct reclaim
Jiri Slaby reported the following:

 > [...]

quoted

quoted

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2624edc..2b7edfa 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -1763,14 +1763,20 @@ static bool in_reclaim_compaction(struct scan_control *sc)
  #ifdef CONFIG_COMPACTION
  /*
   * If compaction is deferred for sc->order then scale the number of pages
- * reclaimed based on the number of consecutive allocation failures
+ * reclaimed based on the number of consecutive allocation failures. This
+ * scaling only happens for direct reclaim as it is about to attempt
+ * compaction. If compaction fails, future allocations will be deferred
+ * and reclaim avoided. On the other hand, kswapd does not take compaction
+ * deferral into account so if it scaled, it could scan excessively even
+ * though allocations are temporarily not being attempted.
   */
  static unsigned long scale_for_compaction(unsigned long pages_for_compaction,
  			struct lruvec *lruvec, struct scan_control *sc)
  {
  	struct zone *zone = lruvec_zone(lruvec);

-	if (zone->compact_order_failed <= sc->order)
+	if (zone->compact_order_failed <= sc->order &&
+	    !current_is_kswapd())
  		pages_for_compaction <<= zone->compact_defer_shift;
  	return pages_for_compaction;
  }

Yes, applying this instead of the revert fixes the issue as well.

Just wondering, is there a reason why this patch wasn't applied to 
mainline? Did it simply fall through the cracks? Or am I missing something?

I'm asking because I think I stil see the issue on 
3.7-rc2-git-checkout-from-friday. Seems Fedora rawhide users are hitting 
it, too:
https://bugzilla.redhat.com/show_bug.cgi?id=866988

Or are we seeing something different which just looks similar? I can 
test the patch if it needs further testing, but from the discussion I 
got the impression that everything is clear and the patch ready for merging.

CU
  knurd

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