linux-kernel - Re: Low overhead patches for the memory cgroup controller (v5)

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Message-Id: <20090622154343.9cdbf23a.akpm@linux-foundation.org>
Date:	Mon, 22 Jun 2009 15:43:43 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	balbir@...ux.vnet.ibm.com
Cc:	kamezawa.hiroyuki@...fujitsu.com, nishimura@....nes.nec.co.jp,
	lizf@...fujitsu.com, menage@...gle.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: Low overhead patches for the memory cgroup controller (v5)

On Mon, 15 Jun 2009 10:09:00 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

>
> ...
> 
> This patch changes the memory cgroup and removes the overhead associated
> with accounting all pages in the root cgroup. As a side-effect, we can
> no longer set a memory hard limit in the root cgroup.
> 
> A new flag to track whether the page has been accounted or not
> has been added as well. Flags are now set atomically for page_cgroup,
> pcg_default_flags is now obsolete and removed.
> 
> ...
>
> @@ -1114,9 +1121,22 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
>  		css_put(&mem->css);
>  		return;
>  	}
> +
>  	pc->mem_cgroup = mem;
>  	smp_wmb();
> -	pc->flags = pcg_default_flags[ctype];
> +	switch (ctype) {
> +	case MEM_CGROUP_CHARGE_TYPE_CACHE:
> +	case MEM_CGROUP_CHARGE_TYPE_SHMEM:
> +		SetPageCgroupCache(pc);
> +		SetPageCgroupUsed(pc);
> +		break;
> +	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
> +		ClearPageCgroupCache(pc);
> +		SetPageCgroupUsed(pc);
> +		break;
> +	default:
> +		break;
> +	}

Do we still need the smp_wmb()?

It's hard to say, because we forgot to document it :(
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