Deferred compaction is employed to avoid compacting zone where sync direct compaction has recently failed. As such, it makes sense to only defer when a full zone was scanned, which is when compact_zone returns with COMPACT_COMPLETE. It's less useful to defer when compact_zone returns with apparent success (COMPACT_PARTIAL), followed by a watermark check failure, which can happen due to parallel allocation activity. It also does not make much sense to defer compaction which was completely skipped (COMPACT_SKIP) for being unsuitable in the first place.
This patch therefore makes deferred compaction trigger only when COMPACT_COMPLETE is returned from compact_zone(). Results of stress-highalloc becnmark show the difference is within measurement error, so the issue is rather cosmetic. Signed-off-by: Vlastimil Babka <[email protected]> Cc: Minchan Kim <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Joonsoo Kim <[email protected]> Cc: Michal Nazarewicz <[email protected]> Cc: Naoya Horiguchi <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Rik van Riel <[email protected]> Cc: David Rientjes <[email protected]> --- mm/compaction.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/compaction.c b/mm/compaction.c index 4b3e0bd..9107588 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1340,7 +1340,7 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist, goto break_loop; } - if (mode != MIGRATE_ASYNC) { + if (mode != MIGRATE_ASYNC && status == COMPACT_COMPLETE) { /* * We think that allocation won't succeed in this zone * so we defer compaction there. If it ends up -- 1.8.4.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
