linux-kernel - Re: [RFC 0/5] Memory controller soft limit introduction (v3)

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Date:	Sat, 28 Jun 2008 13:36:15 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [RFC 0/5] Memory controller soft limit introduction (v3)

On Fri, 27 Jun 2008 20:48:08 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> This patchset implements the basic changes required to implement soft limits
> in the memory controller. A soft limit is a variation of the currently
> supported hard limit feature. A memory cgroup can exceed it's soft limit
> provided there is no contention for memory.
> 
> These patches were tested on a x86_64 box, by running a programs in parallel,
> and checking their behaviour for various soft limit values.
> 
> These patches were developed on top of 2.6.26-rc5-mm3. Comments, suggestions,
> criticism are all welcome!
> 
> A previous version of the patch can be found at
> 
> http://kerneltrap.org/mailarchive/linux-kernel/2008/2/19/904114
> 
I have a couple of comments.

1. Why you add soft_limit to res_coutner ?
   Is there any other controller which uses soft-limit ?
   I'll move watermark handling to memcg from res_counter becasue it's
   required only by memcg.

2. *please* handle NUMA
   There is a fundamental difference between global VMM and memcg.
     global VMM - reclaim memory at memory shortage.
     memcg     - for reclaim memory at memory limit
   Then, memcg wasn't required to handle place-of-memory at hitting limit. 
   *just reducing the usage* was enough.
   In this set, you try to handle memory shortage handling.
   So, please handle NUMA, i.e. "what node do you want to reclaim memory from ?"
   If not, 
    - memory placement of Apps can be terrible.
    - cannot work well with cpuset. (I think)

3. I think  when "mem_cgroup_reclaim_on_contention" exits is unclear.
   plz add explanation of algorithm. It returns when some pages are reclaimed ?

4. When swap-full cgroup is on the top of heap, which tends to contain
   tons of memory, much amount of cpu-time will be wasted.
   Can we add "ignore me" flag  ?

Maybe "2" is the most important to implement this.
I think this feature itself is interesting, so please handle NUMA.

"4" includes the user's (middleware's) memcg handling problem. But maybe
a problem should be fixed in future.

Thanks,
-Kame


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