In async mode, compaction doesn't migrate dirty or writeback pages. So,

it's meaningless to pick the page and re-add it to lru list.

Of course, when we isolate the page in compaction, the page might be dirty
or writeback but when we try to migrate the page, the page would be not
dirty, writeback.  So it could be migrated.  But it's very unlikely as
isolate and migration cycle is much faster than writeout.

So, this patch helps cpu overhead and prevent unnecessary LRU churning.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 4bf3b1eed05aa8dfee8dd07fe7cf359164223aa7..ad4b490b926c0bfac1239a2e2266a31f7ddaa0c4 100644 (file)
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -168,7 +168,8 @@ static inline int is_unevictable_lru(enum lru_list l)
 #define ISOLATE_INACTIVE       ((__force fmode_t)0x1)
 /* Isolate active pages */
 #define ISOLATE_ACTIVE         ((__force fmode_t)0x2)
-
+/* Isolate clean file */
+#define ISOLATE_CLEAN          ((__force fmode_t)0x4)
 /* LRU Isolation modes. */
 typedef unsigned __bitwise__ isolate_mode_t;
 

diff --git a/mm/compaction.c b/mm/compaction.c
index 47f717fa42334552f6d57add946961549b734801..a0e420207ebff3778fc5c17136dc2d5176391105 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -261,6 +261,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *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 = ISOLATE_ACTIVE|ISOLATE_INACTIVE;
 
        /* Do not scan outside zone boundaries */
        low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
@@ -348,9 +349,11 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
                        continue;
                }
 
+               if (!cc->sync)
+                       mode |= ISOLATE_CLEAN;
+
                /* Try isolate the page */
-               if (__isolate_lru_page(page,
-                               ISOLATE_ACTIVE|ISOLATE_INACTIVE, 0) != 0)
+               if (__isolate_lru_page(page, mode, 0) != 0)
                        continue;
 
                VM_BUG_ON(PageTransCompound(page));

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 24054a991d5c3ae7918302701105ccab349be2d1..536b45ddc4c6596bab007969f8de454658c5b7e3 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1046,6 +1046,9 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
 
        ret = -EBUSY;
 
+       if ((mode & ISOLATE_CLEAN) && (PageDirty(page) || PageWriteback(page)))
+               return ret;
+
        if (likely(get_page_unless_zero(page))) {
                /*
                 * Be careful not to clear PageLRU until after we're