Re: [RFD][PATCH] memcg: Move Usage at Task Move

[yamamoto-jCdQPDEk3idL9jVzuh4AOg@public.gmane.org (YAMAMOTO Takashi)]

> > having said that, if you decide to put too large tasks into
> > a cgroup with too small limit, i don't think that there are
> > many choices besides OOM-kill and allowing "exceed".
> > 
> IMHO, allowing exceed is harmfull without changing the definition of "limit".
> "limit" is hard-limit, now, not soft-limit. Changing the defintion just for
> this is not acceptable for me. 

even with the current code, the "exceed" condition can be created
by simply lowering the limit.
(well, i know that some of your patches floating around change it.)

> Maybe "move" under limit itself is crazy ops....Hmm...
> 
> Should we allow task move when the destination cgroup is unlimited ?
> Isn't it useful ?

i think it makes some sense.

> > actually, i think that #3 and #5 are somewhat similar.
> > a big difference is that, while #5 shrinks the cgroup immediately,
> > #3 does it later.  in case we need to do OOM-kill, i prefer to do it
> > sooner than later.
> > 
> #3 will not cause OOM-killer, I hope...A user can notice memory shortage.

we are talking about the case where a cgroup's working set is getting
hopelessly larger than its limit.  i don't see why #3 will not
cause OOM-kill.  can you explain?

YAMAMOTO Takashi