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mm: vmscan: do not scale writeback pages when deciding whether to set ZONE_WRITEBACK 

After the patch "mm: vmscan: Flatten kswapd priority loop" was merged
the scanning priority of kswapd changed.

The priority now rises until it is scanning enough pages to meet the
high watermark.  shrink_inactive_list sets ZONE_WRITEBACK if a number of
pages were encountered under writeback but this value is scaled based on
the priority.  As kswapd frequently scans with a higher priority now it
is relatively easy to set ZONE_WRITEBACK.  This patch removes the
scaling and treates writeback pages similar to how it treats unqueued
dirty pages and congested pages.  The user-visible effect should be that
kswapd will writeback fewer pages from reclaim context.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Mel Gorman 2013-07-08 16:00:25 -07:00 committed by Linus Torvalds
parent 5a1c9cbc15
commit 918fc718c5
1 changed files with 1 additions and 15 deletions
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16
mm/vmscan.c
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@ -1443,25 +1443,11 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
* as there is no guarantee the dirtying process is throttled in the
* same way balance_dirty_pages() manages.
*
* This scales the number of dirty pages that must be under writeback
* before a zone gets flagged ZONE_WRITEBACK. It is a simple backoff
* function that has the most effect in the range DEF_PRIORITY to
* DEF_PRIORITY-2 which is the priority reclaim is considered to be
* in trouble and reclaim is considered to be in trouble.
*
* DEF_PRIORITY 100% isolated pages must be PageWriteback to throttle
* DEF_PRIORITY-1 50% must be PageWriteback
* DEF_PRIORITY-2 25% must be PageWriteback, kswapd in trouble
* ...
* DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
* isolated page is PageWriteback
*
* Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
* of pages under pages flagged for immediate reclaim and stall if any
* are encountered in the nr_immediate check below.
*/
if (nr_writeback && nr_writeback >=
(nr_taken >> (DEF_PRIORITY - sc->priority)))
if (nr_writeback && nr_writeback == nr_taken)
zone_set_flag(zone, ZONE_WRITEBACK);
/*