[Devel] [PATCH RHEL7 COMMIT] ms/mm/compaction: check pageblock suitability once per pageblock

[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 69f425145585fcc7e34a8d9fa3c2eaf14840a304
Author: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Date:   Wed Jan 31 18:21:55 2018 +0300

    ms/mm/compaction: check pageblock suitability once per pageblock
    
    isolation_suitable() and migrate_async_suitable() is used to be sure
    that this pageblock range is fine to be migragted.  It isn't needed to
    call it on every page.  Current code do well if not suitable, but, don't
    do well when suitable.
    
    1) It re-checks isolation_suitable() on each page of a pageblock that was
       already estabilished as suitable.
    2) It re-checks migrate_async_suitable() on each page of a pageblock that
       was not entered through the next_pageblock: label, because
       last_pageblock_nr is not otherwise updated.
    
    This patch fixes situation by 1) calling isolation_suitable() only once
    per pageblock and 2) always updating last_pageblock_nr to the pageblock
    that was just checked.
    
    Additionally, move PageBuddy() check after pageblock unit check, since
    pageblock check is the first thing we should do and makes things more
    simple.
    
    [vbabka at suse.cz: rephrase commit description]
    Signed-off-by: Joonsoo Kim <iamjoonsoo.kim at lge.com>
    Acked-by: Vlastimil Babka <vbabka at suse.cz>
    Cc: Mel Gorman <mgorman at suse.de>
    Cc: Rik van Riel <riel at redhat.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 c122b2087ab94192f2b937e47b563a9c4e688ece)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/compaction.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index c4b6b134b197..ba9fa713038d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -533,25 +533,30 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 
 		/* If isolation recently failed, do not retry */
 		pageblock_nr = low_pfn >> pageblock_order;
-		if (!isolation_suitable(cc, page))
-			goto next_pageblock;
+		if (last_pageblock_nr != pageblock_nr) {
+			int mt;
+
+			last_pageblock_nr = pageblock_nr;
+			if (!isolation_suitable(cc, page))
+				goto next_pageblock;
+
+			/*
+			 * For async migration, also only scan in MOVABLE
+			 * blocks. Async migration is optimistic to see if
+			 * the minimum amount of work satisfies the allocation
+			 */
+			mt = get_pageblock_migratetype(page);
+			if (!cc->sync && !migrate_async_suitable(mt)) {
+				cc->finished_update_migrate = true;
+				skipped_async_unsuitable = true;
+				goto next_pageblock;
+			}
+		}
 
 		/* Skip if free */
 		if (PageBuddy(page))
 			continue;
 
-		/*
-		 * For async migration, also only scan in MOVABLE blocks. Async
-		 * migration is optimistic to see if the minimum amount of work
-		 * satisfies the allocation
-		 */
-		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;
-		}
-
 		/*
 		 * Check may be lockless but that's ok as we recheck later.
 		 * It's possible to migrate LRU pages and balloon pages
@@ -643,7 +648,6 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 
 next_pageblock:
 		low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
-		last_pageblock_nr = pageblock_nr;
 	}
 
 	acct_isolated(zone, locked, cc);