mm/page_alloc: restrict max order of merging on isolated pageblock

Current pageblock isolation logic could isolate each pageblock
individually.  This causes freepage accounting problem if freepage with
pageblock order on isolate pageblock is merged with other freepage on
normal pageblock.  We can prevent merging by restricting max order of
merging to pageblock order if freepage is on isolate pageblock.

A side-effect of this change is that there could be non-merged buddy
freepage even if finishing pageblock isolation, because undoing
pageblock isolation is just to move freepage from isolate buddy list to
normal buddy list rather than to consider merging.  So, the patch also
makes undoing pageblock isolation consider freepage merge.  When
un-isolation, freepage with more than pageblock order and it's buddy are
checked.  If they are on normal pageblock, instead of just moving, we
isolate the freepage and free it in order to get merged.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Heesub Shin <heesub.shin@samsung.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Ritesh Harjani <ritesh.list@gmail.com>
Cc: Gioh Kim <gioh.kim@lge.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 39 insertions, 2 deletions

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 1fa4a4d72ecc..c8778f7e208e 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -76,17 +76,54 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype)
 {
         struct zone *zone;
         unsigned long flags, nr_pages;
+        struct page *isolated_page = NULL;
+        unsigned int order;
+        unsigned long page_idx, buddy_idx;
+        struct page *buddy;
 
         zone = page_zone(page);
         spin_lock_irqsave(&zone->lock, flags);
         if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
                 goto out;
-        nr_pages = move_freepages_block(zone, page, migratetype);
-        __mod_zone_freepage_state(zone, nr_pages, migratetype);
+
+        /*
+         * Because freepage with more than pageblock_order on isolated
+         * pageblock is restricted to merge due to freepage counting problem,
+         * it is possible that there is free buddy page.
+         * move_freepages_block() doesn't care of merge so we need other
+         * approach in order to merge them. Isolation and free will make
+         * these pages to be merged.
+         */
+        if (PageBuddy(page)) {
+                order = page_order(page);
+                if (order >= pageblock_order) {
+                        page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);
+                        buddy_idx = __find_buddy_index(page_idx, order);
+                        buddy = page + (buddy_idx - page_idx);
+
+                        if (!is_migrate_isolate_page(buddy)) {
+                                __isolate_free_page(page, order);
+                                set_page_refcounted(page);
+                                isolated_page = page;
+                        }
+                }
+        }
+
+        /*
+         * If we isolate freepage with more than pageblock_order, there
+         * should be no freepage in the range, so we could avoid costly
+         * pageblock scanning for freepage moving.
+         */
+        if (!isolated_page) {
+                nr_pages = move_freepages_block(zone, page, migratetype);
+                __mod_zone_freepage_state(zone, nr_pages, migratetype);
+        }
         set_pageblock_migratetype(page, migratetype);
         zone->nr_isolate_pageblock--;
 out:
         spin_unlock_irqrestore(&zone->lock, flags);
+        if (isolated_page)
+                __free_pages(isolated_page, order);
 }
 
 static inline struct page *