Hi,

On Mon 28-03-11 11:01:18, Ying Han wrote:

On Mon, Mar 28, 2011 at 2:39 AM, Michal Hocko [off-list ref] wrote:

quoted

Hi all,

Memory cgroups can be currently used to throttle memory usage of a group of
processes. It, however, cannot be used for an isolation of processes from
the rest of the system because all the pages that belong to the group are
also placed on the global LRU lists and so they are eligible for the global
memory reclaim.

This patchset aims at providing an opt-in memory cgroup isolation. This
means that a cgroup can be configured to be isolated from the rest of the
system by means of cgroup virtual filesystem (/dev/memctl/group/memory.isolated).

Thank you Hugh pointing me to the thread. We are working on similar
problem in memcg currently

Here is the problem we see:
1. In memcg, a page is both on per-memcg-per-zone lru and global-lru.
2. Global memory reclaim will throw page away regardless of cgroup.
3. The zone->lru_lock is shared between per-memcg-per-zone lru and global-lru.

This is the primary motivation for the patchset. Except that I do not
insist on the strict isolation because I found opt-in approach less
invasive because you have to know what you are doing while you are
setting up a group. If the thing is enabled by default we can see many
side-effects during the reclaim, I am afraid.

And we know:
1. We shouldn't do global reclaim since it breaks memory isolation.
2. There is no need for a page to be on both LRU list, especially
after having per-memcg background reclaim.

So our approach is to take off page from global lru after it is
charged to a memcg. Only pages allocated at root cgroup remains in
global LRU, and each memcg reclaims pages on its isolated LRU.

This sounds like an instance where all cgroups are isolated by default
(this can be set by mem_cgroup->isolated = 1).

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

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