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Commit 5ee04716 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm, reclaim: cleanup should_continue_reclaim() 

After commit "mm, reclaim: make should_continue_reclaim perform dryrun
detection", closer look at the function shows, that nr_reclaimed == 0
means the function will always return false.  And since non-zero
nr_reclaimed implies non_zero nr_scanned, testing nr_scanned serves no
purpose, and so does the testing for __GFP_RETRY_MAYFAIL.

This patch thus cleans up the function to test only !nr_reclaimed upfront,
and remove the __GFP_RETRY_MAYFAIL test and nr_scanned parameter
completely.  Comment is also updated, explaining that approximating "full
LRU list has been scanned" with nr_scanned == 0 didn't really work.

Link: http://lkml.kernel.org/r/20190806014744.15446-3-mike.kravetz@oracle.com


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Acked-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1c6c1597

mm/vmscan.c

+14 −29
Original line number Diff line number Diff line
@@ -2586,7 +2586,6 @@ static bool in_reclaim_compaction(struct scan_control *sc) 
 */

static inline bool should_continue_reclaim(struct pglist_data *pgdat,

					unsigned long nr_reclaimed,

					unsigned long nr_scanned,

					struct scan_control *sc)

{

	unsigned long pages_for_compaction;
@@ -2597,28 +2596,18 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat, 
	if (!in_reclaim_compaction(sc))

		return false;



	/* Consider stopping depending on scan and reclaim activity */

	if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) {

	/*

		 * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the

		 * full LRU list has been scanned and we are still failing

		 * to reclaim pages. This full LRU scan is potentially

		 * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed

		 */

		if (!nr_reclaimed && !nr_scanned)

			return false;

	} else {

		/*

		 * For non-__GFP_RETRY_MAYFAIL allocations which can presumably

		 * fail without consequence, stop if we failed to reclaim

		 * any pages from the last SWAP_CLUSTER_MAX number of

		 * pages that were scanned. This will return to the

		 * caller faster at the risk reclaim/compaction and

		 * the resulting allocation attempt fails

	 * Stop if we failed to reclaim any pages from the last SWAP_CLUSTER_MAX

	 * number of pages that were scanned. This will return to the caller

	 * with the risk reclaim/compaction and the resulting allocation attempt

	 * fails. In the past we have tried harder for __GFP_RETRY_MAYFAIL

	 * allocations through requiring that the full LRU list has been scanned

	 * first, by assuming that zero delta of sc->nr_scanned means full LRU

	 * scan, but that approximation was wrong, and there were corner cases

	 * where always a non-zero amount of pages were scanned.

	 */

	if (!nr_reclaimed)

		return false;

	}



	/* If compaction would go ahead or the allocation would succeed, stop */

	for (z = 0; z <= sc->reclaim_idx; z++) {
@@ -2645,11 +2634,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat, 
	if (get_nr_swap_pages() > 0)

		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);



	return inactive_lru_pages > pages_for_compaction &&

		/*

		 * avoid dryrun with plenty of inactive pages

		 */

		nr_scanned && nr_reclaimed;

	return inactive_lru_pages > pages_for_compaction;

}



static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
@@ -2794,7 +2779,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) 
			wait_iff_congested(BLK_RW_ASYNC, HZ/10);



	} while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,

					 sc->nr_scanned - nr_scanned, sc));

					 sc));



	/*

	 * Kswapd gives up on balancing particular nodes after too