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Date: Thu, 20 Aug 2009 20:01:21 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: Wu Fengguang <fengguang.wu@...el.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
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 -v2] mm: do batched scans for mem_cgroup
Hi, Wu.
On Thu, Aug 20, 2009 at 1:05 PM, Wu Fengguang<fengguang.wu@...el.com> wrote:
> On Thu, Aug 20, 2009 at 11:13:47AM +0800, KAMEZAWA Hiroyuki wrote:
>> 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.
>
> Good idea, full patch updated with your signed-off-by :)
>
> Thanks,
> Fengguang
> ---
> 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.
Yes. It can scan 32 times pages in only inactive list, not active list.
> 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.
Active list scan would be scanned in 4, inactive list is 32.
>
> 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.
Yes.
> 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.
You mean nr_scan_try_batch logic ?
But that logic works for just global reclaim?
Now am I missing something?
Could you elaborate more? :)
> 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>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.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 2009-07-30 10:45:15.000000000 +0800
> +++ linux/include/linux/mmzone.h 2009-08-20 11:51:08.000000000 +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 2009-08-20 11:48:46.000000000 +0800
> +++ linux/mm/vmscan.c 2009-08-20 12:00:55.000000000 +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 2009-08-20 11:57:54.000000000 +0800
> +++ linux/mm/page_alloc.c 2009-08-20 11:58:39.000000000 +0800
> @@ -3716,7 +3716,7 @@ 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;
>
> --
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>
--
Kind regards,
Minchan Kim
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