On Fri 05-06-15 23:57:59, Tejun Heo wrote: > Hello, Michal. > > On Fri, Jun 05, 2015 at 04:35:34PM +0200, Michal Hocko wrote: > > > That doesn't matter because the detection and TIF_MEMDIE assertion are > > > atomic w.r.t. oom_lock and TIF_MEMDIE essentially extends the locking > > > by preventing further OOM kills. Am I missing something? > > > > This is true but TIF_MEMDIE releasing is not atomic wrt. the allocation > > path. So the oom victim could have released memory and dropped > > This is splitting hairs. In vast majority of problem cases, if > anything is gonna be locked up, it's gonna be locked up before > releasing memory it's holding. Yet again, this is a blunt instrument > to unwedge the system. It's difficult to see the point of aiming that > level of granularity. I was just pointing out that the OOM killer is inherently racy even for the global case. Not sure we are talking about the same thing here. > > > TIF_MEMDIE but the allocation path hasn't noticed that because it's passed > > /* > > * Go through the zonelist yet one more time, keep very high watermark > > * here, this is only to catch a parallel oom killing, we must fail if > > * we're still under heavy pressure. > > */ > > page = get_page_from_freelist(gfp_mask | __GFP_HARDWALL, order, > > ALLOC_WMARK_HIGH|ALLOC_CPUSET, ac); > > > > and goes on to kill another task because there is no TIF_MEMDIE > > anymore. > > Why would this be an issue if we disallow parallel killing? I am confused. The whole thread has started by fixing a race in memcg and I was asking about the global case which is racy currently as well. > > > Deadlocks from infallible allocations getting interlocked are > > > different. OOM killer can't really get around that by itself but I'm > > > not talking about those deadlocks but at the same time they're a lot > > > less likely. It's about OOM victim trapped in a deadlock failing to > > > release memory because someone else is waiting for that memory to be > > > released while blocking the victim. > > > > I thought those would be in the allocator context - which was the > > example I've provided. What kind of context do you have in mind? > > Yeah, sure, they'd be in the allocator context holding other resources > which are being waited upon. The first case was deadlock based on > purely memory starvation where NOFAIL allocations interlock with each > other w/o involving other resources. OK, I guess we were just talking past each other. -- Michal Hocko SUSE Labs -- 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>