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Commit d7f05528 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm, vmscan: account for skipped pages as a partial scan 

Page reclaim determines whether a pgdat is unreclaimable by examining
how many pages have been scanned since a page was freed and comparing
that to the LRU sizes.  Skipped pages are not reclaim candidates but
contribute to scanned.  This can prematurely mark a pgdat as
unreclaimable and trigger an OOM kill.

This patch accounts for skipped pages as a partial scan so that an
unreclaimable pgdat will still be marked as such but by scaling the cost
of a skip, it'll avoid the pgdat being marked prematurely.

Link: http://lkml.kernel.org/r/1469110261-7365-6-git-send-email-mgorman@techsingularity.net


Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f8d1a311

mm/vmscan.c

+18 −2
Original line number Diff line number Diff line
@@ -1424,7 +1424,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 
	LIST_HEAD(pages_skipped);



	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&

					!list_empty(src); scan++) {

					!list_empty(src);) {

		struct page *page;



		page = lru_to_page(src);
@@ -1438,6 +1438,12 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 
			continue;

		}



		/*

		 * Account for scanned and skipped separetly to avoid the pgdat

		 * being prematurely marked unreclaimable by pgdat_reclaimable.

		 */

		scan++;



		switch (__isolate_lru_page(page, mode)) {

		case 0:

			nr_pages = hpage_nr_pages(page);
@@ -1465,14 +1471,24 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 
	 */

	if (!list_empty(&pages_skipped)) {

		int zid;

		unsigned long total_skipped = 0;



		list_splice(&pages_skipped, src);

		for (zid = 0; zid < MAX_NR_ZONES; zid++) {

			if (!nr_skipped[zid])

				continue;



			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);

			total_skipped += nr_skipped[zid];

		}



		/*

		 * Account skipped pages as a partial scan as the pgdat may be

		 * close to unreclaimable. If the LRU list is empty, account

		 * skipped pages as a full scan.

		 */

		scan += list_empty(src) ? total_skipped : total_skipped >> 2;



		list_splice(&pages_skipped, src);

	}

	*nr_scanned = scan;

	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, scan,