Re: [PATCH 4/4] Memory controller soft limit reclaim on contention (v6)

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 16 Mar 2009 17:49:15 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-16 20:58:30]:

> A run away application can do that. Like I mentioned with the tests I
> did for your patches. Soft limits were at 1G/2G and the applications
> (two) tried to touch all the memory in the system. The point is that
> shrink_slab() will be called if the normal system experiences
> watermark issues, soft limits will tackle/control cgroups running out
> of their soft limits and causing memory contention to take place.
> 
Ok, then, how about this ?

 Because our target is "softlimit" and not "memory shortage"
 - don't call soft limit from alloc_pages().
 - don't call soft limit from kswapd and others.
 
Instead of this, add sysctl like this.

  - vm.softlimit_ratio

If vm.softlimit_ratio = 99%, 
  when sum of all usage of memcg is over 99% of system memory,
  softlimit runs and reclaim memory until the whole usage will be below 99%.
   (or some other trigger can be considered.)

Then,
 - We don't have to take care of misc. complicated aspects of memory reclaiming
   We reclaim memory based on our own logic, then, no influence to global LRU.

I think this approach will hide the all corner case and make merging softlimit 
to mainline much easier. If you use this approach, RB-tree is the best one
to go with (and we don't have to care zone's status.)

Thanks,
-Kame

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