On Tue, Jan 17, 2017 at 11:37:01AM +0100, Michal Hocko wrote: > From: Michal Hocko <[email protected]> > > get_scan_count considers the whole node LRU size when > - doing SCAN_FILE due to many page cache inactive pages > - calculating the number of pages to scan > > in both cases this might lead to unexpected behavior especially on 32b > systems where we can expect lowmem memory pressure very often. > > A large highmem zone can easily distort SCAN_FILE heuristic because > there might be only few file pages from the eligible zones on the node > lru and we would still enforce file lru scanning which can lead to > trashing while we could still scan anonymous pages. > > The later use of lruvec_lru_size can be problematic as well. Especially > when there are not many pages from the eligible zones. We would have to > skip over many pages to find anything to reclaim but shrink_node_memcg > would only reduce the remaining number to scan by SWAP_CLUSTER_MAX > at maximum. Therefore we can end up going over a large LRU many times > without actually having chance to reclaim much if anything at all. The > closer we are out of memory on lowmem zone the worse the problem will > be. > > Fix this by filtering out all the ineligible zones when calculating the > lru size for both paths and consider only sc->reclaim_idx zones. > > Acked-by: Minchan Kim <[email protected]> > Acked-by: Hillf Danton <[email protected]> > Signed-off-by: Michal Hocko <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
