lkml.org 
[lkml]   [2009]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH -v2 changelog updated] mm: do batched scans for mem_cgroup
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>
CC: 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>
---
include/linux/mmzone.h | 6 +++++-
mm/page_alloc.c | 2 +-
mm/vmscan.c | 20 +++++++++++---------
3 files changed, 17 insertions(+), 11 deletions(-)

--- linux.orig/include/linux/mmzone.h 2009-08-21 15:02:50.000000000 +0800
+++ linux/include/linux/mmzone.h 2009-08-21 15:03:25.000000000 +0800
@@ -269,6 +269,11 @@ 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 {
@@ -323,7 +328,6 @@ 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;
--- linux.orig/mm/vmscan.c 2009-08-21 15:03:15.000000000 +0800
+++ linux/mm/vmscan.c 2009-08-21 15:03:25.000000000 +0800
@@ -1521,6 +1521,7 @@ static void shrink_zone(int priority, st
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. */
@@ -1540,12 +1541,9 @@ static void shrink_zone(int priority, st
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] ||
@@ -2128,6 +2126,7 @@ static void shrink_all_zones(unsigned lo
{
struct zone *zone;
unsigned long nr_reclaimed = 0;
+ struct zone_reclaim_stat *reclaim_stat;

for_each_populated_zone(zone) {
enum lru_list l;
@@ -2144,11 +2143,14 @@ static void shrink_all_zones(unsigned lo
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);
--- linux.orig/mm/page_alloc.c 2009-08-21 15:02:50.000000000 +0800
+++ linux/mm/page_alloc.c 2009-08-21 15:03:25.000000000 +0800
@@ -3734,7 +3734,7 @@ static void __paginginit free_area_init_
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;

\
 
 \ /
  Last update: 2009-08-21 09:31    [W:0.690 / U:0.352 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site