On 06/10/2015 05:32 AM, Vlastimil Babka wrote:
> Compaction should finish when the migration and free scanner meet, i.e. they
> reach the same pageblock. Currently however, the test in compact_finished()
> simply just compares the exact pfns, which may yield a false negative when the
> free scanner position is in the middle of a pageblock and the migration
> scanner
> reaches the beginning of the same pageblock.
>
> This hasn't been a problem until commit e14c720efdd7 ("mm, compaction:
> remember
> position within pageblock in free pages scanner") allowed the free scanner
> position to be in the middle of a pageblock between invocations. The hot-fix
> 1d5bfe1ffb5b ("mm, compaction: prevent infinite loop in compact_zone")
> prevented the issue by adding a special check in the migration scanner to
> satisfy the current detection of scanners meeting.
>
> However, the proper fix is to make the detection more robust. This patch
> introduces the compact_scanners_met() function that returns true when the free
> scanner position is in the same or lower pageblock than the migration scanner.
> The special case in isolate_migratepages() introduced by 1d5bfe1ffb5b is
> removed.
>
> Suggested-by: Joonsoo Kim <iamjoonsoo....@lge.com>
> Signed-off-by: Vlastimil Babka <vba...@suse.cz>
> Cc: Minchan Kim <minc...@kernel.org>
> Cc: Mel Gorman <mgor...@suse.de>
> Cc: Joonsoo Kim <iamjoonsoo....@lge.com>
> Cc: Michal Nazarewicz <min...@mina86.com>
> Cc: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
> Cc: Christoph Lameter <c...@linux.com>
> Cc: Rik van Riel <r...@redhat.com>
> Cc: David Rientjes <rient...@google.com>
Acked-by: Rik van Riel <r...@redhat.com>
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