On Wed, Nov 27, 2013 at 06:38:31PM -0800, David Rientjes wrote: > On Wed, 27 Nov 2013, Johannes Weiner wrote: > > > > The task that is bypassing the memcg charge to the root memcg may not be > > > the process that is chosen by the oom killer, and it's possible the amount > > > of memory freed by killing the victim is less than the amount of memory > > > bypassed. > > > > That's true, though unlikely. > > > > Well, the "goto bypass" allows it and it's trivial to cause by > manipulating /proc/pid/oom_score_adj values to prefer processes with very > little rss. It will just continue looping and killing processes as they > are forked and never cause the memcg to free memory below its limit. At > least the "goto nomem" allows us to free some memory instead of leaking to > the root memcg. Yes, that's the better way of doing it, I'll send the patch. Thanks. > > > Were you targeting these to 3.13 instead? If so, it would have already > > > appeared in 3.13-rc1 anyway. Is it still a work in progress? > > > > I don't know how to answer this question. > > > > It appears as though this work is being developed in Linus's tree rather > than -mm, so I'm asking if we should consider backing some of it out for > 3.14 instead. The changes fix a deadlock problem. Are they creating problems that are worse than deadlocks, that would justify their revert? > > > Should we be checking mem_cgroup_margin() here to ensure > > > task_in_memcg_oom() is still accurate and we haven't raced by freeing > > > memory? > > > > We would have invoked the OOM killer long before this point prior to > > my patches. There is a line we draw and from that point on we start > > killing things. I tried to explain multiple times now that there is > > no race-free OOM killing and I'm tired of it. Convince me otherwise > > or stop repeating this non-sense. > > > > In our internal kernel we call mem_cgroup_margin() with the order of the > charge immediately prior to sending the SIGKILL to see if it's still > needed even after selecting the victim. It makes the race smaller. > > It's obvious that after the SIGKILL is sent, either from the kernel or > from userspace, that memory might subsequently be freed or another process > might exit before the process killed could even wake up. There's nothing > we can do about that since we don't have psychic abilities. I think we > should try to reduce the chance for unnecessary oom killing as much as > possible, however. Since we can't physically draw a perfect line, we should strive for a reasonable and intuitive line. After that it's rapidly diminishing returns. Killing something after that much reclaim effort without success is a completely reasonable and intuitive line to draw. It's also the line that has been drawn a long time ago and we're not breaking this because of a micro optmimization. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>