Re: [RFC][preview] memcg: reduce lock contention at uncharge by batching

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 26 Aug 2009 14:25:20 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> On Wed, 26 Aug 2009 10:02:56 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > With attached patch below, per-cpu-precharge,
> > 
> > I got this number,
> > 
> > [Before] linux-2.6.31-rc7
> > real    2m46.491s
> > user    4m47.008s
> > sys     3m32.954s
> > 
> > 
> > lock_stat version 0.3
> > -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> >                               class name    con-bounces    contentions   waittime-min   waittime-max waittime-total    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total
> > -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> > 
> >                           &counter->lock:       1167034        1196935           0.52       16291.34      829793.69       18742433       45050576           0.42       30788.81     9490908.36
> >                           --------------
> >                           &counter->lock         638151          [<ffffffff81090fd5>] res_counter_charge+0x45/0xe0
> >                           &counter->lock         558784          [<ffffffff81090f5d>] res_counter_uncharge+0x2d/0x60
> >                           --------------
> >                           &counter->lock         679567          [<ffffffff81090fd5>] res_counter_charge+0x45/0xe0
> >                           &counter->lock         517368          [<ffffffff81090f5d>] res_counter_uncharge+0x2d/0x60
> > 
> > [After] precharge+batched uncharge
> > real    2m46.799s
> > user    4m49.523s
> > sys     3m18.916s
> >                          &counter->lock:         12785          12984           0.71          34.87        6768.24
> >        967813        4937090           0.47       20257.57      953289.67
> >                           --------------
> >                           &counter->lock          11117          [<ffffffff81090f3d>] res_counter_uncharge+0x2d/0x60
> >                           &counter->lock           1867          [<ffffffff81090fb5>] res_counter_charge+0x45/0xe0
> >                           --------------
> >                           &counter->lock          10691          [<ffffffff81090f3d>] res_counter_uncharge+0x2d/0x60
> >                           &counter->lock           2293          [<ffffffff81090fb5>] res_counter_charge+0x45/0xe0
> > 
> > I think patch below is enough simple. (but I need to support flush&cpu-hotplug)
> > I'd like to rebase this onto mmotom. 
> > Main difference with percpu_counter is that this is pre-charge and never goes over limit.
> > 
> I basically agree to this direction, but I have one question.
> 
> What do you mean by "flush" ? I suppose "discard precharges when hitting the limit", right ?
> 

yes.

Thanks,
-Kame

> Thanks,
> Daisuke Nishimura.
> 
> > --
> > Index: linux-2.6.31-rc7/mm/memcontrol.c
> > ===================================================================
> > --- linux-2.6.31-rc7.orig/mm/memcontrol.c	2009-08-26 09:11:57.000000000 +0900
> > +++ linux-2.6.31-rc7/mm/memcontrol.c	2009-08-26 09:46:51.000000000 +0900
> > @@ -67,6 +67,7 @@
> >  	MEM_CGROUP_STAT_PGPGIN_COUNT,	/* # of pages paged in */
> >  	MEM_CGROUP_STAT_PGPGOUT_COUNT,	/* # of pages paged out */
> >  
> > +	MEM_CGROUP_STAT_PRECHARGE, /* # of charges pre-allocated for future */
> >  	MEM_CGROUP_STAT_NSTATS,
> >  };
> >  
> > @@ -959,6 +960,32 @@
> >  	unlock_page_cgroup(pc);
> >  }
> >  
> > +#define CHARGE_SIZE	(4 * ((NR_CPUS >> 5)+1) * PAGE_SIZE)
> > +
> > +bool use_precharge(struct mem_cgroup *mem)
> > +{
> > +	struct mem_cgroup_stat_cpu *cstat;
> > +	int cpu = get_cpu();
> > +	bool ret = true;
> > +
> > +	cstat = &mem->stat.cpustat[cpu];
> > +	if (cstat->count[MEM_CGROUP_STAT_PRECHARGE])
> > +		cstat->count[MEM_CGROUP_STAT_PRECHARGE] -= PAGE_SIZE;
> > +	else
> > +		ret = false;
> > +	put_cpu();
> > +	return ret;
> > +}
> > +
> > +void do_precharge(struct mem_cgroup *mem, int val)
> > +{
> > +	struct mem_cgroup_stat_cpu *cstat;
> > +	int cpu = get_cpu();
> > +	cstat = &mem->stat.cpustat[cpu];
> > +	__mem_cgroup_stat_add_safe(cstat, MEM_CGROUP_STAT_PRECHARGE, val);
> > +	put_cpu();
> > +}
> > +
> >  /*
> >   * Unlike exported interface, "oom" parameter is added. if oom==true,
> >   * oom-killer can be invoked.
> > @@ -995,20 +1022,24 @@
> >  
> >  	VM_BUG_ON(css_is_removed(&mem->css));
> >  
> > +	/* can we use precharge ? */
> > +	if (use_precharge(mem))
> > +		goto got;
> > +
> >  	while (1) {
> >  		int ret;
> >  		bool noswap = false;
> >  
> > -		ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res);
> > +		ret = res_counter_charge(&mem->res, CHARGE_SIZE, &fail_res);
> >  		if (likely(!ret)) {
> >  			if (!do_swap_account)
> >  				break;
> > -			ret = res_counter_charge(&mem->memsw, PAGE_SIZE,
> > +			ret = res_counter_charge(&mem->memsw, CHARGE_SIZE,
> >  							&fail_res);
> >  			if (likely(!ret))
> >  				break;
> >  			/* mem+swap counter fails */
> > -			res_counter_uncharge(&mem->res, PAGE_SIZE);
> > +			res_counter_uncharge(&mem->res, CHARGE_SIZE);
> >  			noswap = true;
> >  			mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> >  									memsw);
> > @@ -1046,6 +1077,8 @@
> >  			goto nomem;
> >  		}
> >  	}
> > +	do_precharge(mem, CHARGE_SIZE-PAGE_SIZE);
> > +got:
> >  	return 0;
> >  nomem:
> >  	css_put(&mem->css);
> > 
> 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>