[PATCH 3.14 28/37] mm, compaction: determine isolation mode only once

From: Greg Kroah-Hartman
Date: Tue Oct 07 2014 - 19:28:12 EST


3.14-stable review patch. If anyone has any objections, please let me know.

------------------

From: David Rientjes <rientjes@xxxxxxxxxx>

commit da1c67a76f7cf2b3404823d24f9f10fa91aa5dc5 upstream.

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@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
mm/compaction.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)

--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -460,12 +460,13 @@ isolate_migratepages_range(struct zone *
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
@@ -608,12 +609,6 @@ isolate_migratepages_range(struct zone *
continue;
}

- if (!cc->sync)
- mode |= ISOLATE_ASYNC_MIGRATE;
-
- if (unevictable)
- mode |= ISOLATE_UNEVICTABLE;
-
lruvec = mem_cgroup_page_lruvec(page, zone);

/* Try isolate the page */


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