Re: [PATCH 3/7] memcg: immigrate charges only when a threadgroup leader is moved

[Tejun Heo <tj@kernel.org>]

On Thu, May 21, 2015 at 04:12:26PM +0200, Michal Hocko wrote:
> On Mon 18-05-15 15:49:51, Tejun Heo wrote:
> > If move_charge flag is set, memcg tries to move memory charges to the
> > destnation css.  The current implementation migrates memory whenever
> > any thread of a process is migrated making the behavior somewhat
> > arbitrary.  Let's tie memory operations to the threadgroup leader so
> > that memory is migrated only when the leader is migrated.
> > 
> > While this is a behavior change, given the inherent fuziness, this
> > change is not too likely to be noticed and allows us to clearly define
> > who owns the memory (always the leader) and helps the planned atomic
> > multi-process migration.
> > 
> > Signed-off-by: Tejun Heo <tj@kernel.org>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Michal Hocko <mhocko@suse.cz>
> 
> OK, I guess the discussion with Oleg confirmed that the patch is not
> really needed because mm_struct->owner check implies thread group
> leader. This should be sufficient for your purpose Tejun, right?

Hmmm... we still need to update so that it actually iterates leaders
to find the owner as first in taskset == leader assumption is going
away but yeah this patch in itself can go away.  I'll update the next
patch accordingly.

Thanks.

-- 
tejun

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