On 09/26/2011 07:52 AM, KAMEZAWA Hiroyuki wrote:

On Sat, 24 Sep 2011 11:45:04 -0300
Glauber Costa[off-list ref]  wrote:

quoted

On 09/22/2011 12:09 PM, Balbir Singh wrote:

quoted

On Thu, Sep 22, 2011 at 11:30 AM, Greg Thelen[off-list ref]   wrote:

quoted

On Wed, Sep 21, 2011 at 11:59 AM, Glauber Costa[off-list ref]   wrote:

quoted

Right now I am working under the assumption that tasks are long lived inside
the cgroup. Migration potentially introduces some nasty locking problems in
the mem_schedule path.

Also, unless I am missing something, the memcg already has the policy of
not carrying charges around, probably because of this very same complexity.

True that at least it won't EBUSY you... But I think this is at least a way
to guarantee that the cgroup under our nose won't disappear in the middle of
our allocations.

Here's the memcg user page behavior using the same pattern:

1. user page P is allocate by task T in memcg M1
2. T is moved to memcg M2.  The P charge is left behind still charged
to M1 if memory.move_charge_at_immigrate=0; or the charge is moved to
M2 if memory.move_charge_at_immigrate=1.
3. rmdir M1 will try to reclaim P (if P was left in M1).  If unable to
reclaim, then P is recharged to parent(M1).

We also have some magic in page_referenced() to remove pages
referenced from different containers. What we do is try not to
penalize a cgroup if another cgroup is referencing this page and the
page under consideration is being reclaimed from the cgroup that
touched it.

Balbir Singh

Do you guys see it as a showstopper for this series to be merged, or can
we just TODO it ?

In my experience, 'I can't rmdir cgroup.' is always an important/difficult
problem. The users cannot know where the accouting is leaking other than
kmem.usage_in_bytes or memory.usage_in_bytes. and can't fix the issue.

please add EXPERIMENTAL to Kconfig until this is fixed.

quoted

I can push a proposal for it, but it would be done in a separate patch
anyway. Also, we may be in better conditions to fix this when the slab
part is merged - since it will likely have the same problems...

Yes. considering sockets which can be shared between tasks(cgroups)
you'll finally need
   - owner task of socket
   - account moving callback

Or disallow task moving once accounted.

So,

I tried to come up with proper task charge moving here, and the locking 
easily gets quite complicated. (But I have the feeling I am overlooking 
something...) So I think I'll really need more time for that.

What do you guys think of this following patch, + EXPERIMENTAL ?