linux-kernel - Re: [PATCH] meminfo: show /proc/meminfo base on container's memcg

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Date:	Wed, 30 May 2012 17:35:38 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
cc:	Gao feng <gaofeng@...fujitsu.com>, hannes@...xchg.org,
	kamezawa.hiroyu@...fujitsu.com, mhocko@...e.cz,
	bsingharora@...il.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, containers@...ts.linux-foundation.org
Subject: Re: [PATCH] meminfo: show /proc/meminfo base on container's memcg

On Thu, 31 May 2012, Kirill A. Shutemov wrote:

> > Why?  Because the information exported by /proc/meminfo is considered by 
> > applications to be static whereas the limit of a memcg may change without 
> > any knowledge of the application.
> 
> Memory hotplug does the same, right?
> 

Memory hotplug is a seperate topic, it changes the amount of physical 
memory that is available to the kernel, not any limitation of memory 
available to a set of tasks.  For memory hot-add, this does not 
automatically increase the memory.limit_in_bytes of any non-root memcg, 
the memory usage is still constrained as it was before the hotplug event.  
Thus, applications would want to depend on memory.{limit,usage}_in_bytes 
specifically to determine the amount of available memory even with 
CONFIG_MEMORY_HOTPLUG.

Also, under certain cirucmstances such as when a thread is oom killed, it 
may allocate memory in excess of its memcg limitation and this wouldn't be 
visible as available with this patch via /proc/meminfo.  Cpusets allows 
softwall allocations even when a thread is simply exiting on all nodes 
(and for GFP_ATOMIC allocations) and this also wouldn't be visible in 
/proc/meminfo.
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