From 246e87a9393448c20873bc5dee64be68ed559e24 Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Thu, 26 May 2011 16:25:34 -0700 Subject: [PATCH] memcg: fix get_scan_count() for small targets During memory reclaim we determine the number of pages to be scanned per zone as (anon + file) >> priority. Assume scan = (anon + file) >> priority. If scan < SWAP_CLUSTER_MAX, the scan will be skipped for this time and priority gets higher. This has some problems. 1. This increases priority as 1 without any scan. To do scan in this priority, amount of pages should be larger than 512M. If pages>>priority < SWAP_CLUSTER_MAX, it's recorded and scan will be batched, later. (But we lose 1 priority.) If memory size is below 16M, pages >> priority is 0 and no scan in DEF_PRIORITY forever. 2. If zone->all_unreclaimabe==true, it's scanned only when priority==0. So, x86's ZONE_DMA will never be recoverred until the user of pages frees memory by itself. 3. With memcg, the limit of memory can be small. When using small memcg, it gets priority < DEF_PRIORITY-2 very easily and need to call wait_iff_congested(). For doing scan before priorty=9, 64MB of memory should be used. Then, this patch tries to scan SWAP_CLUSTER_MAX of pages in force...when 1. the target is enough small. 2. it's kswapd or memcg reclaim. Then we can avoid rapid priority drop and may be able to recover all_unreclaimable in a small zones. And this patch removes nr_saved_scan. This will allow scanning in this priority even when pages >> priority is very small. Signed-off-by: KAMEZAWA Hiroyuki Acked-by: Ying Han Cc: Balbir Singh Cc: KOSAKI Motohiro Cc: Daisuke Nishimura Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mmzone.h | 5 ---- mm/page_alloc.c | 4 +-- mm/vmscan.c | 60 +++++++++++++++++++++++------------------- 3 files changed, 34 insertions(+), 35 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 217bcf6bca77..29312bdf119f 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -273,11 +273,6 @@ struct zone_reclaim_stat { */ unsigned long recent_rotated[2]; unsigned long recent_scanned[2]; - - /* - * accumulated for batching - */ - unsigned long nr_saved_scan[NR_LRU_LISTS]; }; struct zone { diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2a00f17c3bf4..a4e1db3f1981 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4323,10 +4323,8 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat, zone->zone_pgdat = pgdat; zone_pcp_init(zone); - for_each_lru(l) { + for_each_lru(l) INIT_LIST_HEAD(&zone->lru[l].list); - zone->reclaim_stat.nr_saved_scan[l] = 0; - } zone->reclaim_stat.recent_rotated[0] = 0; zone->reclaim_stat.recent_rotated[1] = 0; zone->reclaim_stat.recent_scanned[0] = 0; diff --git a/mm/vmscan.c b/mm/vmscan.c index b0875871820d..2e8fbacd8744 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1717,26 +1717,6 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, return shrink_inactive_list(nr_to_scan, zone, sc, priority, file); } -/* - * Smallish @nr_to_scan's are deposited in @nr_saved_scan, - * until we collected @swap_cluster_max pages to scan. - */ -static unsigned long nr_scan_try_batch(unsigned long nr_to_scan, - unsigned long *nr_saved_scan) -{ - unsigned long nr; - - *nr_saved_scan += nr_to_scan; - nr = *nr_saved_scan; - - if (nr >= SWAP_CLUSTER_MAX) - *nr_saved_scan = 0; - else - nr = 0; - - return nr; -} - /* * Determine how aggressively the anon and file LRU lists should be * scanned. The relative value of each set of LRU lists is determined @@ -1755,6 +1735,22 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc, u64 fraction[2], denominator; enum lru_list l; int noswap = 0; + int force_scan = 0; + + + anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) + + zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON); + file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) + + zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); + + if (((anon + file) >> priority) < SWAP_CLUSTER_MAX) { + /* kswapd does zone balancing and need to scan this zone */ + if (scanning_global_lru(sc) && current_is_kswapd()) + force_scan = 1; + /* memcg may have small limit and need to avoid priority drop */ + if (!scanning_global_lru(sc)) + force_scan = 1; + } /* If we have no swap space, do not bother scanning anon pages. */ if (!sc->may_swap || (nr_swap_pages <= 0)) { @@ -1765,11 +1761,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc, goto out; } - anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) + - zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON); - file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) + - zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); - if (scanning_global_lru(sc)) { free = zone_page_state(zone, NR_FREE_PAGES); /* If we have very few page cache pages, @@ -1836,8 +1827,23 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc, scan >>= priority; scan = div64_u64(scan * fraction[file], denominator); } - nr[l] = nr_scan_try_batch(scan, - &reclaim_stat->nr_saved_scan[l]); + + /* + * If zone is small or memcg is small, nr[l] can be 0. + * This results no-scan on this priority and priority drop down. + * For global direct reclaim, it can visit next zone and tend + * not to have problems. For global kswapd, it's for zone + * balancing and it need to scan a small amounts. When using + * memcg, priority drop can cause big latency. So, it's better + * to scan small amount. See may_noscan above. + */ + if (!scan && force_scan) { + if (file) + scan = SWAP_CLUSTER_MAX; + else if (!noswap) + scan = SWAP_CLUSTER_MAX; + } + nr[l] = scan; } }