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Date: Tue, 7 Apr 2009 09:04:38 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: balbir@...ux.vnet.ibm.com Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com> Subject: Re: [RFC][PATCH 3/9] soft limit update filter On Mon, 6 Apr 2009 15:13:51 +0530 Balbir Singh <balbir@...ux.vnet.ibm.com> wrote: > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-04-03 17:12:02]: > > > No changes from v1. > > == > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> > > > > Check/Update softlimit information at every charge is over-killing, so > > we need some filter. > > > > This patch tries to count events in the memcg and if events > threshold > > tries to update memcg's soft limit status and reset event counter to 0. > > > > Event counter is maintained by per-cpu which has been already used, > > Then, no siginificant overhead(extra cache-miss etc..) in theory. > > > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> > > --- > > Index: mmotm-2.6.29-Mar23/mm/memcontrol.c > > =================================================================== > > --- mmotm-2.6.29-Mar23.orig/mm/memcontrol.c > > +++ mmotm-2.6.29-Mar23/mm/memcontrol.c > > @@ -66,6 +66,7 @@ enum mem_cgroup_stat_index { > > MEM_CGROUP_STAT_PGPGIN_COUNT, /* # of pages paged in */ > > MEM_CGROUP_STAT_PGPGOUT_COUNT, /* # of pages paged out */ > > > > + MEM_CGROUP_STAT_EVENTS, /* sum of page-in/page-out for internal use */ > > MEM_CGROUP_STAT_NSTATS, > > }; > > > > @@ -105,6 +106,22 @@ static s64 mem_cgroup_local_usage(struct > > return ret; > > } > > > > +/* For intenal use of per-cpu event counting. */ > > + > > +static inline void > > +__mem_cgroup_stat_reset_safe(struct mem_cgroup_stat_cpu *stat, > > + enum mem_cgroup_stat_index idx) > > +{ > > + stat->count[idx] = 0; > > +} > > Why do we do this and why do we need a special event? > 2 points. 1. we do "reset" this counter. 2. We're counting page-in/page-out. I wonder I should counter others... > > + > > +static inline s64 > > +__mem_cgroup_stat_read_local(struct mem_cgroup_stat_cpu *stat, > > + enum mem_cgroup_stat_index idx) > > +{ > > + return stat->count[idx]; > > +} > > + > > /* > > * per-zone information in memory controller. > > */ > > @@ -235,6 +252,8 @@ static void mem_cgroup_charge_statistics > > else > > __mem_cgroup_stat_add_safe(cpustat, > > MEM_CGROUP_STAT_PGPGOUT_COUNT, 1); > > + __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_EVENTS, 1); > > + > > put_cpu(); > > } > > > > @@ -897,9 +916,26 @@ static void record_last_oom(struct mem_c > > mem_cgroup_walk_tree(mem, NULL, record_last_oom_cb); > > } > > > > +#define SOFTLIMIT_EVENTS_THRESH (1024) /* 1024 times of page-in/out */ > > +/* > > + * Returns true if sum of page-in/page-out events since last check is > > + * over SOFTLIMIT_EVENT_THRESH. (counter is per-cpu.) > > + */ > > static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem) > > { > > - return false; > > + bool ret = false; > > + int cpu = get_cpu(); > > + s64 val; > > + struct mem_cgroup_stat_cpu *cpustat; > > + > > + cpustat = &mem->stat.cpustat[cpu]; > > + val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_EVENTS); > > + if (unlikely(val > SOFTLIMIT_EVENTS_THRESH)) { > > + __mem_cgroup_stat_reset_safe(cpustat, MEM_CGROUP_STAT_EVENTS); > > + ret = true; > > + } > > + put_cpu(); > > + return ret; > > } > > > > It is good to have the caller and the function in the same patch. > Otherwise, you'll notice unused warnings. I think this function can be > simplified further > > 1. Lets gid rid of MEM_CGRUP_STAT_EVENTS > 2. Lets rewrite mem_cgroup_soft_limit_check as > > static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem) > { > bool ret = false; > int cpu = get_cpu(); > s64 pgin, pgout; > struct mem_cgroup_stat_cpu *cpustat; > > cpustat = &mem->stat.cpustat[cpu]; > pgin = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_PGPGIN_COUNT); > pgout = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_PGPGOUT_COUNT); > val = pgin + pgout - mem->last_event_count; > if (unlikely(val > SOFTLIMIT_EVENTS_THRESH)) { > mem->last_event_count = pgin + pgout; > ret = true; > } > put_cpu(); > return ret; > } > > mem->last_event_count can either be atomic or protected using one of > the locks you intend to introduce. This will avoid the overhead of > incrementing event at every charge_statistics. > Incrementing always hits cache. Hmm, making mem->last_event_count as per-cpu, we can do above. And maybe no difference with current code. But you don't seem to like counting, it's ok to change the shape. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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