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SubjectRe: [PATCH 3/3] compaction accouting fix
On Sun, Nov 13, 2011 at 01:37:43AM +0900, Minchan Kim wrote:
> I saw the following accouting of compaction during test of the series.
> compact_blocks_moved 251
> compact_pages_moved 44
> It's very awkward to me although it's possbile because it means we try to compact 251 blocks
> but it just migrated 44 pages. As further investigation, I found isolate_migratepages doesn't
> isolate any pages but it returns ISOLATE_SUCCESS and then, it just increases compact_blocks_moved
> but doesn't increased compact_pages_moved.
> This patch makes accouting of compaction works only in case of success of isolation.
> CC: Mel Gorman <>
> CC: Johannes Weiner <>
> CC: Rik van Riel <>
> Signed-off-by: Minchan Kim <>

Acked-by: Johannes Weiner <>

It's a teensy-bit awkward that isolate_migratepages() can return
success without actually isolating any new pages, just because there
are still some pages left from a previous run (cc->nr_migratepages is
maintained across isolation calls).

Maybe isolate_migratepages() should just return an error if compaction
should really be aborted and 0 otherwise, and have compact_zone()
always check for cc->nr_migratepages itself?

if (isolate_migratepages(zone, cc) < 0) {
goto out;

if (!cc->nr_migratepages)


Just a nit-pick, though. If you don't agree, just leave it as is.

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