linux-kernel - Re: [PATCH v3 07/11] memcg: add dirty limits to mem

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Message-ID: <xr93iq0x1p6z.fsf@ninji.mtv.corp.google.com>
Date:	Tue, 19 Oct 2010 21:08:20 -0700
From:	Greg Thelen <gthelen@...gle.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v3 07/11] memcg: add dirty limits to mem_cgroup

Daisuke Nishimura <nishimura@....nes.nec.co.jp> writes:

>> +static unsigned long long
>> +memcg_hierarchical_free_pages(struct mem_cgroup *mem)
>> +{
>> +	struct cgroup *cgroup;
>> +	unsigned long long min_free, free;
>> +
>> +	min_free = res_counter_read_u64(&mem->res, RES_LIMIT) -
>> +		res_counter_read_u64(&mem->res, RES_USAGE);
>> +	cgroup = mem->css.cgroup;
>> +	if (!mem->use_hierarchy)
>> +		goto out;
>> +
>> +	while (cgroup->parent) {
>> +		cgroup = cgroup->parent;
>> +		mem = mem_cgroup_from_cont(cgroup);
>> +		if (!mem->use_hierarchy)
>> +			break;
>> +		free = res_counter_read_u64(&mem->res, RES_LIMIT) -
>> +			res_counter_read_u64(&mem->res, RES_USAGE);
>> +		min_free = min(min_free, free);
>> +	}
>> +out:
>> +	/* Translate free memory in pages */
>> +	return min_free >> PAGE_SHIFT;
>> +}
>> +
> I think you can simplify this function using parent_mem_cgroup().
>
> 	unsigned long free, min_free = ULLONG_MAX;
>
> 	while (mem) {
> 		free = res_counter_read_u64(&mem->res, RES_LIMIT) -
> 			res_counter_read_u64(&mem->res, RES_USAGE);
> 		min_free = min(min_free, free);
> 		mem = parent_mem_cgroup();
> 	}
>
> 	/* Translate free memory in pages */
> 	return min_free >> PAGE_SHIFT;
>
> And, IMHO, we should return min(global_page_state(NR_FREE_PAGES), min_free >> PAGE_SHIFT).
> Because we are allowed to set no-limit(or a very big limit) in memcg,
> so min_free can be very big if we don't set a limit against all the memcg's in hierarchy.
>
>
> Thanks,
> Dasiuke Nishimura.

Thank you.  This is a good suggestion.  I will update the page to include this.

--
Greg
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