On 12/14/2011 10:41 AM, Mel Gorman wrote:
If compaction can proceed for a given zone, shrink_zones() does not reclaim any more pages from it. After commit [e0c2327: vmscan: abort reclaim/compaction if compaction can proceed], do_try_to_free_pages() tries to finish as soon as possible once one zone can compact. This was intended to prevent slabs being shrunk unnecessarily but there are side-effects. One is that a small zone that is ready for compaction will abort reclaim even if the chances of successfully allocating a THP from that zone is small. It also means that reclaim can return too early even though sc->nr_to_reclaim pages were not reclaimed.
Having slabs shrunk "too much" might actually be good, because it does result in more memory blocks where compaction can be successful. If we end up frequently evicting frequently accessed data from the slab cache, chances are the buffer cache will cache that data (since we reload it often). If we end up evicting infrequently used data, chances are it won't really matter for performance.
This partially reverts the commit until it is proven that slabs are really being shrunk unnecessarily but preserves the check to return 1 to avoid OOM if reclaim was aborted prematurely. [aarcange@xxxxxxxxxx: This patch replaces a revert from Andrea] Signed-off-by: Mel Gorman<mgorman@xxxxxxx>
Reviewed-by: Rik van Riel<riel@xxxxxxxxxx> -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>