linux-kernel - Re: [patch 4/8] mm: memcg: push !mm handling out to page cache charge function

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Message-ID: <20140312131152.GC11831@dhcp22.suse.cz>
Date:	Wed, 12 Mar 2014 14:11:52 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 4/8] mm: memcg: push !mm handling out to page cache
 charge function

On Tue 11-03-14 21:28:30, Johannes Weiner wrote:
[...]
> @@ -4070,6 +4061,12 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
>  		return 0;
>  
>  	if (!PageSwapCache(page)) {
> +		/*
> +		 * Page cache insertions can happen without an actual
> +		 * task context, e.g. during disk probing on boot.

We read a page cache during disk probing? I have tried to find such a
code path but failed. Could you point me to such a path, please?
I thought that such probing is done from udev context but I am not
familiar with this area TBH.

Thanks!

> +		 */
> +		if (!mm)
> +			memcg = root_mem_cgroup;
>  		ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &memcg, true);
>  		if (ret != -ENOMEM)
>  			__mem_cgroup_commit_charge(memcg, page, 1, type, false);
> -- 
> 1.9.0
> 

-- 
Michal Hocko
SUSE Labs
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