[Devel] [PATCH RHEL7 COMMIT] ms/mm: compaction: do not mark unmovable pageblocks as skipped in async compaction

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.11.6.vz7.42.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.11.6.vz7.42.4
------>
commit bab8a4ef40873cb44b563bac226e7f9e19e6f7bf
Author: Vlastimil Babka <vbabka at suse.cz>
Date:   Wed Jan 31 18:21:51 2018 +0300

    ms/mm: compaction: do not mark unmovable pageblocks as skipped in async compaction
    
    Compaction temporarily marks pageblocks where it fails to isolate pages
    as to-be-skipped in further compactions, in order to improve efficiency.
    One of the reasons to fail isolating pages is that isolation is not
    attempted in pageblocks that are not of MIGRATE_MOVABLE (or CMA) type.
    
    The problem is that blocks skipped due to not being MIGRATE_MOVABLE in
    async compaction become skipped due to the temporary mark also in future
    sync compaction.  Moreover, this may follow quite soon during
    __alloc_page_slowpath, without much time for kswapd to clear the
    pageblock skip marks.  This goes against the idea that sync compaction
    should try to scan these blocks more thoroughly than the async
    compaction.
    
    The fix is to ensure in async compaction that these !MIGRATE_MOVABLE
    blocks are not marked to be skipped.  Note this should not affect
    performance or locking impact of further async compactions, as skipping
    a block due to being !MIGRATE_MOVABLE is done soon after skipping a
    block marked to be skipped, both without locking.
    
    Signed-off-by: Vlastimil Babka <vbabka at suse.cz>
    Cc: Rik van Riel <riel at redhat.com>
    Acked-by: Mel Gorman <mgorman at suse.de>
    Cc: Joonsoo Kim <iamjoonsoo.kim at lge.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    (cherry picked from commit 50b5b094e683f8e51e82c6dfe97b1608cf97e6c0)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/compaction.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index f324cbaf923d..8ebf3d10ef17 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -472,6 +472,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 	unsigned long flags;
 	bool locked = false;
 	struct page *page = NULL, *valid_page = NULL;
+	bool skipped_async_unsuitable = false;
 
 	/*
 	 * Ensure that there are not too many pages isolated from the LRU
@@ -547,6 +548,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 		if (!cc->sync && last_pageblock_nr != pageblock_nr &&
 		    !migrate_async_suitable(get_pageblock_migratetype(page))) {
 			cc->finished_update_migrate = true;
+			skipped_async_unsuitable = true;
 			goto next_pageblock;
 		}
 
@@ -640,8 +642,13 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 	if (locked)
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
 
-	/* Update the pageblock-skip if the whole pageblock was scanned */
-	if (low_pfn == end_pfn)
+	/*
+	 * Update the pageblock-skip information and cached scanner pfn,
+	 * if the whole pageblock was scanned without isolating any page.
+	 * This is not done when pageblock was skipped due to being unsuitable
+	 * for async compaction, so that eventual sync compaction can try.
+	 */
+	if (low_pfn == end_pfn && !skipped_async_unsuitable)
 		update_pageblock_skip(cc, valid_page, nr_isolated, true);
 
 	trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);