vmscan: comment too_many_isolated()

Fengguang Wu · torvalds · commit d37dd5dcb955 · 2012-12-18T15:02:15.000-08:00
Comment "Why it's doing so" rather than "What it does" as proposed by
Andrew Morton.

Signed-off-by: Wu Fengguang &lt;fengguang.wu@intel.com&gt;
Reviewed-by: KOSAKI Motohiro &lt;kosaki.motohiro@jp.fujitsu.com&gt;
Reviewed-by: Minchan Kim &lt;minchan.kim@gmail.com&gt;
Reviewed-by: Rik van Riel &lt;riel@redhat.com&gt;
Cc: Mel Gorman &lt;mel@csn.ul.ie&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git a/mm/vmscan.c b/mm/vmscan.c
@@ -1177,7 +1177,11 @@ int isolate_lru_page(struct page *page)
 }
 
 /*
- * Are there way too many processes in the direct reclaim path already?
+ * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
+ * then get resheduled. When there are massive number of tasks doing page
+ * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
+ * the LRU list will go small and be scanned faster than necessary, leading to
+ * unnecessary swapping, thrashing and OOM.
  */
 static int too_many_isolated(struct zone *zone, int file,
 		struct scan_control *sc)
