linux-kernel - Re: [PATCH] Help Resource Counters Scale better (v4.1)

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Message-Id: <20090813140840.125b31fb.nishimura@mxp.nes.nec.co.jp>
Date:	Thu, 13 Aug 2009 14:08:40 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	balbir@...ux.vnet.ibm.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	kamezawa.hiroyu@...fujitsu.com, kosaki.motohiro@...fujitsu.com,
	menage@...gle.com, prarit@...hat.com, andi.kleen@...el.com,
	xemul@...nvz.org, lizf@...fujitsu.com, nishimura@....nes.nec.co.jp,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Help Resource Counters Scale better (v4.1)

On Thu, 13 Aug 2009 09:03:35 +0530, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> * nishimura@....nes.nec.co.jp <nishimura@....nes.nec.co.jp> [2009-08-13 10:03:50]:
> 
> > > @@ -1855,9 +1883,14 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> > >  		break;
> > >  	}
> > >  
> > > -	res_counter_uncharge(&mem->res, PAGE_SIZE, &soft_limit_excess);
> > > -	if (do_swap_account && (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
> > > -		res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
> > > +	if (!mem_cgroup_is_root(mem)) {
> > > +		res_counter_uncharge(&mem->res, PAGE_SIZE, &soft_limit_excess);
> > > +		if (do_swap_account &&
> > > +				(ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
> > > +			res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
> > > +	}
> > > +	if (ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT && mem_cgroup_is_root(mem))
> > > +		mem_cgroup_swap_statistics(mem, true);
> > I think mem_cgroup_is_root(mem) would be unnecessary here.
> > Otherwise, MEM_CGROUP_STAT_SWAPOUT of groups except root memcgroup wouldn't
> > be counted properly.
> > 
> 
> I think you have a valid point, but it will not impact us currently
> since we use SWAPOUT only for root accounting.
> 
> > 
> > > @@ -2461,10 +2496,26 @@ static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
> > >  	name = MEMFILE_ATTR(cft->private);
> > >  	switch (type) {
> > >  	case _MEM:
> > > -		val = res_counter_read_u64(&mem->res, name);
> > > +		if (name == RES_USAGE && mem_cgroup_is_root(mem)) {
> > > +			val = mem_cgroup_read_stat(&mem->stat,
> > > +					MEM_CGROUP_STAT_CACHE);
> > > +			val += mem_cgroup_read_stat(&mem->stat,
> > > +					MEM_CGROUP_STAT_RSS);
> > > +			val <<= PAGE_SHIFT;
> > > +		} else
> > > +			val = res_counter_read_u64(&mem->res, name);
> > >  		break;
> > >  	case _MEMSWAP:
> > > -		val = res_counter_read_u64(&mem->memsw, name);
> > > +		if (name == RES_USAGE && mem_cgroup_is_root(mem)) {
> > > +			val = mem_cgroup_read_stat(&mem->stat,
> > > +					MEM_CGROUP_STAT_CACHE);
> > > +			val += mem_cgroup_read_stat(&mem->stat,
> > > +					MEM_CGROUP_STAT_RSS);
> > > +			val += mem_cgroup_read_stat(&mem->stat,
> > > +					MEM_CGROUP_STAT_SWAPOUT);
> > > +			val <<= PAGE_SHIFT;
> > > +		} else
> > > +			val = res_counter_read_u64(&mem->memsw, name);
> > >  		break;
> > >  	default:
> > >  		BUG();
> > Considering use_hierarchy==1 case in the root memcgroup, shouldn't we use
> > mem_cgroup_walk_tree() here to sum up all the children's usage ?
> > *.usage_in_bytes show sum of all the children's usage now if use_hierarchy==1.
> 
> If memory.use_hiearchy=1, we should use total_stats..right. Let me
> send out a newer version for review.
> 
BTW, I don't think the patch title is suitable for this patch.
This patch doesn't make res_counter scalable at all :)

Of course, I think the patch using percpu_counter for scalability is also important.


Thanks,
Daisuke Nishimura.
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