On Sun, Mar 17, 2013 at 01:04:07PM +0000, Mel Gorman wrote: > The number of pages kswapd can reclaim is bound by the number of pages it > scans which is related to the size of the zone and the scanning priority. In > many cases the priority remains low because it's reset every SWAP_CLUSTER_MAX > reclaimed pages but in the event kswapd scans a large number of pages it > cannot reclaim, it will raise the priority and potentially discard a large > percentage of the zone as sc->nr_to_reclaim is ULONG_MAX. The user-visible > effect is a reclaim "spike" where a large percentage of memory is suddenly > freed. It would be bad enough if this was just unused memory but because > of how anon/file pages are balanced it is possible that applications get > pushed to swap unnecessarily. > > This patch limits the number of pages kswapd will reclaim to the high > watermark. Reclaim will will overshoot due to it not being a hard limit as will -> still? > shrink_lruvec() will ignore the sc.nr_to_reclaim at DEF_PRIORITY but it > prevents kswapd reclaiming the world at higher priorities. The number of > pages it reclaims is not adjusted for high-order allocations as kswapd will > reclaim excessively if it is to balance zones for high-order allocations. I don't really understand this last sentence. Is the excessive reclaim a result of the patch, a description of what's happening now...? > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> Nice, thank you. Using the high watermark for larger zones is more reasonable than my hack that just always went with SWAP_CLUSTER_MAX, what with inter-zone LRU cycle time balancing and all. Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>