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Commit 491d79ae authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

mm: remove unnecessary back-off function when retrying page reclaim 

The backoff mechanism is not needed.  If we have MAX_RECLAIM_RETRIES
loops without progress, we'll OOM anyway; backing off might cut one or
two iterations off that in the rare OOM case.  If we have intermittent
success reclaiming a few pages, the backoff function gets reset also,
and so is of little help in these scenarios.

We might want a backoff function for when there IS progress, but not
enough to be satisfactory.  But this isn't that.  Remove it.

Link: http://lkml.kernel.org/r/20170228214007.5621-10-hannes@cmpxchg.org


Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarHillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Jia He <hejianet@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3db65812

mm/page_alloc.c

+6 −9
Original line number Diff line number Diff line
@@ -3515,11 +3515,10 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask) 
/*

 * Checks whether it makes sense to retry the reclaim to make a forward progress

 * for the given allocation request.

 * The reclaim feedback represented by did_some_progress (any progress during

 * the last reclaim round) and no_progress_loops (number of reclaim rounds without

 * any progress in a row) is considered as well as the reclaimable pages on the

 * applicable zone list (with a backoff mechanism which is a function of

 * no_progress_loops).

 *

 * We give up when we either have tried MAX_RECLAIM_RETRIES in a row

 * without success, or when we couldn't even meet the watermark if we

 * reclaimed all remaining pages on the LRU lists.

 *

 * Returns true if a retry is viable or false to enter the oom path.

 */
@@ -3564,13 +3563,11 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order, 
		bool wmark;



		available = reclaimable = zone_reclaimable_pages(zone);

		available -= DIV_ROUND_UP((*no_progress_loops) * available,

					  MAX_RECLAIM_RETRIES);

		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);



		/*

		 * Would the allocation succeed if we reclaimed the whole

		 * available?

		 * Would the allocation succeed if we reclaimed all

		 * reclaimable pages?

		 */

		wmark = __zone_watermark_ok(zone, order, min_wmark,

				ac_classzone_idx(ac), alloc_flags, available);