[Devel] Re: [lxc-devel] Memory Resources

[Daniel Lezcano]

KAMEZAWA Hiroyuki wrote:
> On Mon, 24 Aug 2009 16:11:15 +0200
> Daniel Lezcano <daniel.lezcano at free.fr> wrote:
>
>   
>> [ snip ]
>>     
>>>>> i think that /proc/meminfo should be mounted after /proc . why? i think
>>>>> that, because mounting /proc may override /proc/meminfo
>>>>> Am I right? :)
>>>>>
>>>>>
>>>>>       
>>>>>           
>>>> Ha ! haha ! arrgh ! no way ! You are right :/
>>>>
>>>>     
>>>>         
>>> Hehe ;)
>>>
>>>   
>>>       
>>>> In the case of application container, lxc mounts /proc but in the case of
>>>> system container it is the system who do that so after the /proc/meminfo has
>>>> been mounted.
>>>>
>>>> Maybe we can look at modifying fs/proc/meminfo.c instead. Let me do a small
>>>> patch for the kernel...
>>>>
>>>>
>>>>     
>>>>         
>>> Okey. I am waiting for your patch :)
>>>       
>> Quick and dirty patch but at least working. It is no synced on the 
>> latest kernel version.
>> I do not really like to touch fs/proc/meminfo.c but it's an example here.
>>
>>     
>
> I'll strongly Nack to this.
> plz find a way to 
> ln -s /path_to_cgroup/memory.meminfo   /mycontainer/meminfo
>   

Yep, I agree with you, I don't like this approach.

We are trying to solve the problem of the userspace tools which look at 
the /proc/meminfo file to display memory informations. That looks weird 
to set a max memory usage of 256MB via the cgroup and having the 'free' 
command showing 4GB of total memory. More than looking weird, Dietmar 
explained that can puzzle applications relying on these informations for 
taking some decisions.

If we consider having /cgroup/mycontainer/memory.meminfo with memory 
information in the same format than /proc/meminfo, that solves partially 
the problem:
 - we run an application container, the application won't mount /proc so 
the lxc tools do that for the application (at least to isolate the pids 
information), it is easy to mount --bind 
/cgroup/mycontainer/memory.meminfo to /proc/meminfo before the 
application takes the control, that is to say before 'exec'. Tested and 
verified with the memory tools (free, top, etc ...)

 - we run a system container, we can do this mount-bind but when the 
application, aka /sbin/init, takes the control, the /proc is mounted by 
the system services, so we lose the /proc/meminfo we previously set. 
Hence meminfo in the cgroup directory does not solve the problem for 
this use case.

Any ideas ?

Thanks
  -- Daniel


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