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Date: Thu, 20 Aug 2009 12:13:47 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Wu Fengguang <fengguang.wu@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Rik van Riel <riel@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Avi Kivity <avi@...hat.com>,
Andrea Arcangeli <aarcange@...hat.com>,
"Dike, Jeffrey G" <jeffrey.g.dike@...el.com>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Christoph Lameter <cl@...ux-foundation.org>,
Mel Gorman <mel@....ul.ie>,
LKML <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
"menage@...gle.com" <menage@...gle.com>
Subject: Re: [PATCH] mm: do batched scans for mem_cgroup
On Thu, 20 Aug 2009 10:49:29 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:
> 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, it will be scanned SWAP_CLUSTER_MAX=32 pages in effect.
>
> 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.
>
> This batching won't blur up the cgroup limits, since it is driven by
> "pages reclaimed" rather than "pages scanned". When shrink_zone()
> decides to cancel (and save) one smallish scan, it may well be called
> again to accumulate up nr_saved_scan.
>
> It could possibly be a problem for some tiny mem_cgroup (which may be
> _full_ scanned too much times in order to accumulate up nr_saved_scan).
>
> CC: Rik van Riel <riel@...hat.com>
> CC: Minchan Kim <minchan.kim@...il.com>
> CC: Balbir Singh <balbir@...ux.vnet.ibm.com>
> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
Hmm, how about this ?
==
Now, nr_saved_scan is tied to zone's LRU.
But, considering how vmscan works, it should be tied to reclaim_stat.
By this, memcg can make use of nr_saved_scan information seamlessly.
---
include/linux/mmzone.h | 2 +-
mm/vmscan.c | 19 ++++++++++---------
2 files changed, 11 insertions(+), 10 deletions(-)
Index: linux-2.6.31-rc6/include/linux/mmzone.h
===================================================================
--- linux-2.6.31-rc6.orig/include/linux/mmzone.h 2009-08-17 15:14:21.000000000 +0900
+++ linux-2.6.31-rc6/include/linux/mmzone.h 2009-08-20 12:10:44.000000000 +0900
@@ -269,6 +269,7 @@
*/
unsigned long recent_rotated[2];
unsigned long recent_scanned[2];
+ unsigned long nr_saved_scan[NR_LRU_LISTS];/* accumulated for batching */
};
struct zone {
@@ -323,7 +324,6 @@
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;
Index: linux-2.6.31-rc6/mm/vmscan.c
===================================================================
--- linux-2.6.31-rc6.orig/mm/vmscan.c 2009-08-17 15:14:21.000000000 +0900
+++ linux-2.6.31-rc6/mm/vmscan.c 2009-08-20 12:17:47.000000000 +0900
@@ -1521,6 +1521,7 @@
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 @@
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,
+ &recalim_stat->nr_saved_scan[l],
+ swap_cluster_max);
}
while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
@@ -2128,6 +2126,7 @@
{
struct zone *zone;
unsigned long nr_reclaimed = 0;
+ struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
for_each_populated_zone(zone) {
enum lru_list l;
@@ -2144,11 +2143,13 @@
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->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);
--
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