On Wed, Jun 26, 2013 at 12:39:25PM -0700, Andrew Morton wrote:
> On Wed, 26 Jun 2013 13:39:23 +0100 Mel Gorman <mgorman@xxxxxxx> wrote:
>
> > Page reclaim at priority 0 will scan the entire LRU as priority 0 is
> > considered to be a near OOM condition. Direct reclaim can reach this
> > priority while still making reclaim progress. This patch avoids
> > reclaiming at priority 0 unless no reclaim progress was made and
> > the page allocator would consider firing the OOM killer. The
> > user-visible impact is that direct reclaim will not easily reach
> > priority 0 and start swapping prematurely.
>
> That's a bandaid.
>
> Priority 0 should be a pretty darn rare condition. How often is it
> occurring, and do you know why?
>
There are no flys on you.
The actual rescanning never happens in my experience but priority 0
is reached quickly. Instrumentation showed that it was due to a bug in
reclaim/compaction. Please consider replacing the patch with this.
---8<---
mm: vmscan: Do not continue scanning if reclaim was aborted for compaction
Direct reclaim is not aborting to allow compaction to go ahead properly.
do_try_to_free_pages is told to abort reclaim which is happily ignores
and instead increases priority instead until it reaches 0 and starts
shrinking file/anon equally. This patch corrects the situation by
aborting reclaim when requested instead of raising priority.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/vmscan.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2a5dee2..2f0193c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2381,8 +2381,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
aborted_reclaim = shrink_zones(zonelist, sc);
/*
- * Don't shrink slabs when reclaiming memory from
- * over limit cgroups
+ * Don't shrink slabs when reclaiming memory from over limit
+ * cgroups but do shrink slab at least once when aborting
+ * reclaim for compaction to avoid unevenly scanning file/anon
+ * LRU pages over slab pages.
*/
if (global_reclaim(sc)) {
unsigned long lru_pages = 0;
@@ -2428,7 +2430,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
WB_REASON_TRY_TO_FREE_PAGES);
sc->may_writepage = 1;
}
- } while (--sc->priority >= 0);
+ } while (--sc->priority >= 0 && !aborted_reclaim);
out:
delayacct_freepages_end();
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>