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Date: Wed, 22 Jun 2011 17:53:09 +0200
From: Michal Hocko <mhocko@...e.cz>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"bsingharora@...il.com" <bsingharora@...il.com>,
Ying Han <yinghan@...gle.com>,
"hannes@...xchg.org" <hannes@...xchg.org>
Subject: Re: [PATCH 4/7] memcg: update numa information based on event counter
On Thu 16-06-11 12:54:00, KAMEZAWA Hiroyuki wrote:
> From 88090fe10e225ad8769ba0ea01692b7314e8b973 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Date: Wed, 15 Jun 2011 16:19:46 +0900
> Subject: [PATCH 4/7] memcg: update numa information based on event counter
>
> commit 889976 adds an numa node round-robin for memcg. But the information
> is updated once per 10sec.
>
> This patch changes the update trigger from jiffies to memcg's event count.
> After this patch, numa scan information will be updated when
>
> - the number of pagein/out events is larger than 3% of limit
> or
> - the number of pagein/out events is larger than 16k
> (==64MB pagein/pageout if pagesize==4k.)
>
> The counter of mem->numascan_update the sum of percpu events counter.
> When a task hits limit, it checks mem->numascan_update. If it's over
> min(3% of limit, 16k), numa information will be updated.
Yes, I like the event based approach more than the origin (time) based
one.
>
> This patch also adds mutex for updating information. This will allow us
> to avoid unnecessary scan.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> mm/memcontrol.c | 51 +++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 45 insertions(+), 6 deletions(-)
>
> Index: mmotm-0615/mm/memcontrol.c
> ===================================================================
> --- mmotm-0615.orig/mm/memcontrol.c
> +++ mmotm-0615/mm/memcontrol.c
> @@ -108,10 +108,12 @@ enum mem_cgroup_events_index {
> enum mem_cgroup_events_target {
> MEM_CGROUP_TARGET_THRESH,
> MEM_CGROUP_TARGET_SOFTLIMIT,
> + MEM_CGROUP_TARGET_NUMASCAN,
Shouldn't it be defined only for MAX_NUMNODES > 1
> MEM_CGROUP_NTARGETS,
> };
> #define THRESHOLDS_EVENTS_TARGET (128)
> #define SOFTLIMIT_EVENTS_TARGET (1024)
> +#define NUMASCAN_EVENTS_TARGET (1024)
>
> struct mem_cgroup_stat_cpu {
> long count[MEM_CGROUP_STAT_NSTATS];
> @@ -288,8 +290,9 @@ struct mem_cgroup {
> int last_scanned_node;
> #if MAX_NUMNODES > 1
> nodemask_t scan_nodes;
> - unsigned long next_scan_node_update;
> + struct mutex numascan_mutex;
> #endif
> + atomic_t numascan_update;
Why it is out of ifdef?
> /*
> * Should the accounting and control be hierarchical, per subtree?
> */
> @@ -741,6 +744,9 @@ static void __mem_cgroup_target_update(s
> case MEM_CGROUP_TARGET_SOFTLIMIT:
> next = val + SOFTLIMIT_EVENTS_TARGET;
> break;
> + case MEM_CGROUP_TARGET_NUMASCAN:
> + next = val + NUMASCAN_EVENTS_TARGET;
> + break;
MAX_NUMNODES > 1
> default:
> return;
> }
> @@ -764,6 +770,13 @@ static void memcg_check_events(struct me
> __mem_cgroup_target_update(mem,
> MEM_CGROUP_TARGET_SOFTLIMIT);
> }
> + if (unlikely(__memcg_event_check(mem,
> + MEM_CGROUP_TARGET_NUMASCAN))) {
> + atomic_add(MEM_CGROUP_TARGET_NUMASCAN,
> + &mem->numascan_update);
> + __mem_cgroup_target_update(mem,
> + MEM_CGROUP_TARGET_NUMASCAN);
> + }
> }
again MAX_NUMNODES > 1
> }
>
> @@ -1616,17 +1629,32 @@ mem_cgroup_select_victim(struct mem_cgro
> /*
> * Always updating the nodemask is not very good - even if we have an empty
> * list or the wrong list here, we can start from some node and traverse all
> - * nodes based on the zonelist. So update the list loosely once per 10 secs.
> + * nodes based on the zonelist.
> *
> + * The counter of mem->numascan_update is updated once per
> + * NUMASCAN_EVENTS_TARGET. We update the numa information when we see
> + * the number of event is larger than 3% of limit or 64MB pagein/pageout.
> */
> +#define NUMASCAN_UPDATE_RATIO (3)
> +#define NUMASCAN_UPDATE_THRESH (16384UL) /* 16k events of pagein/pageout */
> static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
> {
> int nid;
> -
> - if (time_after(mem->next_scan_node_update, jiffies))
> + unsigned long long limit;
> + /* if no limit, we never reach here */
> + limit = res_counter_read_u64(&mem->res, RES_LIMIT);
> + limit /= PAGE_SIZE;
> + /* 3% of limit */
> + limit = (limit * NUMASCAN_UPDATE_RATIO/100UL);
> + limit = min_t(unsigned long long, limit, NUMASCAN_UPDATE_THRESH);
> + /*
> + * If the number of pagein/out event is larger than 3% of limit or
> + * 64MB pagein/out, refresh numa information.
> + */
> + if (atomic_read(&mem->numascan_update) < limit ||
> + !mutex_trylock(&mem->numascan_mutex))
> return;
I am not sure whether a mutex is not overkill here. What about using an
atomic operation instead?
> -
> - mem->next_scan_node_update = jiffies + 10*HZ;
> + atomic_set(&mem->numascan_update, 0);
> /* make a nodemask where this memcg uses memory from */
> mem->scan_nodes = node_states[N_HIGH_MEMORY];
>
> @@ -1642,6 +1670,7 @@ static void mem_cgroup_may_update_nodema
> continue;
> node_clear(nid, mem->scan_nodes);
> }
> + mutex_unlock(&mem->numascan_mutex);
> }
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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