From d778df51c09264076fe0208c099ef7d428f21790 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Fri, 22 Feb 2013 16:32:12 -0800 Subject: mm: vmscan: save work scanning (almost) empty LRU lists In certain cases (kswapd reclaim, memcg target reclaim), a fixed minimum amount of pages is scanned from the LRU lists on each iteration, to make progress. Do not make this minimum bigger than the respective LRU list size, however, and save some busy work trying to isolate and reclaim pages that are not there. Empty LRU lists are quite common with memory cgroups in NUMA environments because there exists a set of LRU lists for each zone for each memory cgroup, while the memory of a single cgroup is expected to stay on just one node. The number of expected empty LRU lists is thus memcgs * (nodes - 1) * lru types Each attempt to reclaim from an empty LRU list does expensive size comparisons between lists, acquires the zone's lru lock etc. Avoid that. Signed-off-by: Johannes Weiner Reviewed-by: Rik van Riel Acked-by: Mel Gorman Reviewed-by: Michal Hocko Cc: Hugh Dickins Cc: Satoru Moriya Cc: Simon Jeons Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) (limited to 'mm/vmscan.c') diff --git a/mm/vmscan.c b/mm/vmscan.c index ff842d9a771..e4521ba1ddd 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1761,15 +1761,17 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, out: for_each_evictable_lru(lru) { int file = is_file_lru(lru); + unsigned long size; unsigned long scan; - scan = get_lru_size(lruvec, lru); + size = get_lru_size(lruvec, lru); if (sc->priority || noswap || !vmscan_swappiness(sc)) { - scan >>= sc->priority; + scan = size >> sc->priority; if (!scan && force_scan) - scan = SWAP_CLUSTER_MAX; + scan = min(size, SWAP_CLUSTER_MAX); scan = div64_u64(scan * fraction[file], denominator); - } + } else + scan = size; nr[lru] = scan; } } -- cgit v1.2.3-70-g09d2