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mm: do batched scans for mem_cgroup

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For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, in
which case shrink_list() _still_ calls isolate_pages() with the much
larger SWAP_CLUSTER_MAX.  It effectively scales up the inactive list scan
rate by up to 32 times.

For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4.
So when shrink_zone() expects to scan 4 pages in the active/inactive list,
the active list will be scanned 4 pages, while the inactive list will be
(over) scanned SWAP_CLUSTER_MAX=32 pages in effect.  And that could break
the balance between the two lists.

It can further impact the scan of anon active list, due to the anon
active/inactive ratio rebalance logic in balance_pgdat()/shrink_zone():

inactive anon list over scanned => inactive_anon_is_low() == TRUE
                                => shrink_active_list()
                                => active anon list over scanned

So the end result may be

- anon inactive  => over scanned
- anon active    => over scanned (maybe not as much)
- file inactive  => over scanned
- file active    => under scanned (relatively)

The accesses to nr_saved_scan are not lock protected and so not 100%
accurate, however we can tolerate small errors and the resulted small
imbalanced scan rates between zones.

Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Wu Fengguang 2009-09-21 17:03:11 -07:00 committed by Linus Torvalds
parent 1a8670a29b
commit f862963174
3 changed files with 17 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/mmzone.h
View File

@ -273,6 +273,11 @@ 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 {
@ -327,7 +332,6 @@ struct zone {
spinlock_t lru_lock;
struct zone_lru {
struct list_head list;
unsigned long nr_saved_scan; /* accumulated for batching */
} lru[NR_LRU_LISTS];
struct zone_reclaim_stat reclaim_stat;

2
mm/page_alloc.c
View File

@ -3809,7 +3809,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
zone_pcp_init(zone);
for_each_lru(l) {
INIT_LIST_HEAD(&zone->lru[l].list);
zone->lru[l].nr_saved_scan = 0;
zone->reclaim_stat.nr_saved_scan[l] = 0;
}
zone->reclaim_stat.recent_rotated[0] = 0;
zone->reclaim_stat.recent_rotated[1] = 0;

20
mm/vmscan.c
View File

@ -1586,6 +1586,7 @@ static void shrink_zone(int priority, struct zone *zone,
enum lru_list l;
unsigned long nr_reclaimed = sc->nr_reclaimed;
unsigned long swap_cluster_max = sc->swap_cluster_max;
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
int noswap = 0;
/* If we have no swap space, do not bother scanning anon pages. */
@ -1605,12 +1606,9 @@ static void shrink_zone(int priority, struct zone *zone,
scan >>= priority;
scan = (scan * percent[file]) / 100;
}
if (scanning_global_lru(sc))
nr[l] = nr_scan_try_batch(scan,
&zone->lru[l].nr_saved_scan,
swap_cluster_max);
else
nr[l] = scan;
nr[l] = nr_scan_try_batch(scan,
&reclaim_stat->nr_saved_scan[l],
swap_cluster_max);
}
while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
@ -2220,6 +2218,7 @@ static void shrink_all_zones(unsigned long nr_pages, int prio,
{
struct zone *zone;
unsigned long nr_reclaimed = 0;
struct zone_reclaim_stat *reclaim_stat;
for_each_populated_zone(zone) {
enum lru_list l;
@ -2236,11 +2235,14 @@ static void shrink_all_zones(unsigned long nr_pages, int prio,
l == LRU_ACTIVE_FILE))
continue;
zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1;
if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) {
reclaim_stat = get_reclaim_stat(zone, sc);
reclaim_stat->nr_saved_scan[l] +=
(lru_pages >> prio) + 1;
if (reclaim_stat->nr_saved_scan[l]
>= nr_pages || pass > 3) {
unsigned long nr_to_scan;
zone->lru[l].nr_saved_scan = 0;
reclaim_stat->nr_saved_scan[l] = 0;
nr_to_scan = min(nr_pages, lru_pages);
nr_reclaimed += shrink_list(l, nr_to_scan, zone,
sc, prio);