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From: KOSAKI Motohiro on 5 Aug 2010 02:20
congestion_wait() mean "waiting quueue congestion is cleared".
That said, if the system have plenty dirty pages and flusher thread push
new request to IO queue conteniously, IO queue are not cleared
congestion status for long time. thus, congestion_wait(HZ/10) become
almostly equivalent schedule_timeout(HZ/10).

However, synchronous lumpy reclaim donesn't need this
congestion_wait() at all. shrink_page_list(PAGEOUT_IO_SYNC) are
using wait_on_page_writeback() and it provide sufficient waiting.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com>
---
mm/vmscan.c | 1 -
1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index cf51d62..1cdc3db 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1341,7 +1341,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,

/* Check if we should syncronously wait for writeback */
if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
- congestion_wait(BLK_RW_ASYNC, HZ/10);
/*
* The attempt at page out may have made some
* of the pages active, mark them inactive again.
--
1.6.5.2



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