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vmscan: comment too_many_isolated()

PATCH RESEND New Fengguang Wu 1 participant 1 message Dec 10, 2012

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PATCH RESEND 1/1 vmscan: comment too_many_isolated()

Comment "Why it's doing so" rather than "What it does" as proposed by Andrew Morton.

---
 mm/vmscan.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
mm/vmscan.c +5 -1
@@ -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)

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