linux-kernel - Re: memcg: cat: memory.memsw.* : Operation not supported

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Message-ID: <20120627154827.GA4420@tiehlicka.suse.cz>
Date:	Wed, 27 Jun 2012 17:48:27 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Zhouping Liu <zliu@...hat.com>
Cc:	linux-mm@...ck.org, Li Zefan <lizefan@...wei.com>,
	Tejun Heo <tj@...nel.org>, CAI Qian <caiqian@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: memcg: cat: memory.memsw.* : Operation not supported

On Tue 26-06-12 23:49:15, Zhouping Liu wrote:
> hi, all
> 
> when I used memory cgroup in latest mainline, the following error occurred:
> 
> # mount -t cgroup -o memory xxx /cgroup/
> # ll /cgroup/memory.memsw.*
> -rw-r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.failcnt
> -rw-r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.limit_in_bytes
> -rw-r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.max_usage_in_bytes
> -r--r--r--. 1 root root 0 Jun 26 23:17 /cgroup/memory.memsw.usage_in_bytes
> # cat /cgroup/memory.memsw.*
> cat: /cgroup/memory.memsw.failcnt: Operation not supported
> cat: /cgroup/memory.memsw.limit_in_bytes: Operation not supported
> cat: /cgroup/memory.memsw.max_usage_in_bytes: Operation not supported
> cat: /cgroup/memory.memsw.usage_in_bytes: Operation not supported
> 
> I'm confusing why it can't read memory.memsw.* files.

Those files are exported if CONFIG_CGROUP_MEM_RES_CTLR_SWAP=y even
if the feature is turned off when any attempt to open the file returns
EOPNOTSUPP which is exactly what you are seeing.
This is a deliberate decision see: b6d9270d (memcg: always create memsw
files if CONFIG_CGROUP_MEM_RES_CTLR_SWAP).

Does this help to explain your problem? Do you actually see any problem
with this behavior?

Thanks
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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