mm: remove unnecessary back-off function when retrying page reclaim (491d79ae) · Commits · 戴 / test

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:

Johannes Weiner <hannes@cmpxchg.org> Acked-by:

Hillf Danton <hillf.zj@alibaba-inc.com> Acked-by:

Michal Hocko <mhocko@suse.com> Cc: Jia He <hejianet@gmail.com> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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);

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