On Wed, May 07 2014, Vlastimil Babka wrote:
> The compaction free scanner in isolate_freepages() currently remembers PFN of
> the highest pageblock where it successfully isolates, to be used as the
> starting pageblock for the next invocation. The rationale behind this is that
> page migration might return free pages to the allocator when migration fails
> and we don't want to skip them if the compaction continues.
>
> Since migration now returns free pages back to compaction code where they can
> be reused, this is no longer a concern. This patch changes isolate_freepages()
> so that the PFN for restarting is updated with each pageblock where isolation
> is attempted. Using stress-highalloc from mmtests, this resulted in 10%
> reduction of the pages scanned by the free scanner.
>
> Note that the somewhat similar functionality that records highest successful
> pageblock in zone->compact_cached_free_pfn, remains unchanged. This cache is
> used when the whole compaction is restarted, not for multiple invocations of
> the free scanner during single compaction.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Cc: Michal Nazarewicz <mina86@mina86.com>

Acked-by: Michal Nazarewicz <mina86@mina86.com>

> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Rik van Riel <riel@redhat.com>
> ---
>  v2: no changes, just keep patches together
>
>  mm/compaction.c | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
>
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