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authorMel Gorman <mgorman@suse.de>2013-07-04 02:01:51 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-04 03:07:28 +0400
commit283aba9f9e0e4882bf09bd37a2983379a6fae805 (patch)
tree8c856efae71bb2daaadae48ff565132dd6e0b06b /include
parentd43006d503ac921c7df4f94d13c17db6f13c9d26 (diff)
downloadlinux-283aba9f9e0e4882bf09bd37a2983379a6fae805.tar.xz
mm: vmscan: block kswapd if it is encountering pages under writeback
Historically, kswapd used to congestion_wait() at higher priorities if it was not making forward progress. This made no sense as the failure to make progress could be completely independent of IO. It was later replaced by wait_iff_congested() and removed entirely by commit 258401a6 (mm: don't wait on congested zones in balance_pgdat()) as it was duplicating logic in shrink_inactive_list(). This is problematic. If kswapd encounters many pages under writeback and it continues to scan until it reaches the high watermark then it will quickly skip over the pages under writeback and reclaim clean young pages or push applications out to swap. The use of wait_iff_congested() is not suited to kswapd as it will only stall if the underlying BDI is really congested or a direct reclaimer was unable to write to the underlying BDI. kswapd bypasses the BDI congestion as it sets PF_SWAPWRITE but even if this was taken into account then it would cause direct reclaimers to stall on writeback which is not desirable. This patch sets a ZONE_WRITEBACK flag if direct reclaim or kswapd is encountering too many pages under writeback. If this flag is set and kswapd encounters a PageReclaim page under writeback then it'll assume that the LRU lists are being recycled too quickly before IO can complete and block waiting for some IO to complete. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Michal Hocko <mhocko@suse.cz> Acked-by: Rik van Riel <riel@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Tested-by: Zlatko Calusic <zcalusic@bitsync.net> Cc: dormando <dormando@rydia.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/mmzone.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2aaf72f7e345..fce64afba042 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -499,6 +499,9 @@ typedef enum {
* many dirty file pages at the tail
* of the LRU.
*/
+ ZONE_WRITEBACK, /* reclaim scanning has recently found
+ * many pages under writeback
+ */
} zone_flags_t;
static inline void zone_set_flag(struct zone *zone, zone_flags_t flag)
@@ -526,6 +529,11 @@ static inline int zone_is_reclaim_dirty(const struct zone *zone)
return test_bit(ZONE_TAIL_LRU_DIRTY, &zone->flags);
}
+static inline int zone_is_reclaim_writeback(const struct zone *zone)
+{
+ return test_bit(ZONE_WRITEBACK, &zone->flags);
+}
+
static inline int zone_is_reclaim_locked(const struct zone *zone)
{
return test_bit(ZONE_RECLAIM_LOCKED, &zone->flags);