[Devel] [PATCH RHEL7 COMMIT] ms/mm, compaction: determine isolation mode only once

[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 6179ca1f3376f3b2da3826a051adecfcdc77fef1
Author: David Rientjes <rientjes at google.com>
Date:   Wed Jan 31 18:21:56 2018 +0300

    ms/mm, compaction: determine isolation mode only once
    
    The conditions that control the isolation mode in
    isolate_migratepages_range() do not change during the iteration, so
    extract them out and only define the value once.
    
    This actually does have an effect, gcc doesn't optimize it itself because
    of cc->sync.
    
    Signed-off-by: David Rientjes <rientjes at google.com>
    Cc: Mel Gorman <mgorman at suse.de>
    Acked-by: Rik van Riel <riel at redhat.com>
    Acked-by: Vlastimil Babka <vbabka at suse.cz>
    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 da1c67a76f7cf2b3404823d24f9f10fa91aa5dc5)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/compaction.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index d833777ddaee..9f2abe03d1aa 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -467,12 +467,13 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 	unsigned long last_pageblock_nr = 0, pageblock_nr;
 	unsigned long nr_scanned = 0, nr_isolated = 0;
 	struct list_head *migratelist = &cc->migratepages;
-	isolate_mode_t mode = 0;
 	struct lruvec *lruvec;
 	unsigned long flags;
 	bool locked = false;
 	struct page *page = NULL, *valid_page = NULL;
 	bool skipped_async_unsuitable = false;
+	const isolate_mode_t mode = (!cc->sync ? ISOLATE_ASYNC_MIGRATE : 0) |
+				    (unevictable ? ISOLATE_UNEVICTABLE : 0);
 
 	/*
 	 * Ensure that there are not too many pages isolated from the LRU
@@ -612,12 +613,6 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 			continue;
 		}
 
-		if (!cc->sync)
-			mode |= ISOLATE_ASYNC_MIGRATE;
-
-		if (unevictable)
-			mode |= ISOLATE_UNEVICTABLE;
-
 		lruvec = mem_cgroup_page_lruvec(page, zone);
 
 		/* Try isolate the page */