On 21.10.2021 14:49, Michal Hocko wrote: > On Thu 21-10-21 11:03:43, Vasily Averin wrote: >> On 18.10.2021 12:04, Michal Hocko wrote: >>> On Mon 18-10-21 11:13:52, Vasily Averin wrote: >>> [...] >>>> How could this happen? >>>> >>>> User-space task inside the memcg-limited container generated a page fault, >>>> its handler do_user_addr_fault() called handle_mm_fault which could not >>>> allocate the page due to exceeding the memcg limit and returned VM_FAULT_OOM. >>>> Then do_user_addr_fault() called pagefault_out_of_memory() which executed >>>> out_of_memory() without set of memcg. >> >>> I will be honest that I am not really happy about pagefault_out_of_memory. >>> I have tried to remove it in the past. Without much success back then, >>> unfortunately[1]. >>> >>> [1] I do not have msg-id so I cannot provide a lore link but google >>> pointed me to https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1400402.html >> >> I re-read this discussion and in general I support your position. >> As far as I understand your opponents cannot explain why "random kill" is mandatory here, >> they are just afraid that it might be useful here and do not want to remove it completely. > > That aligns with my recollection. > >> Ok, let's allow him to do it. Moreover I'm ready to keep it as default behavior. >> >> However I would like to have some choice in this point. >> >> In general we can: >> - continue to use "random kill" and rely on the wisdom of the ancestors. > > I do not follow. Does that mean to preserve existing oom killer from > #PF? > >> - do nothing, repeat #PF and rely on fate: "nothing bad will happen if we do it again". >> - add some (progressive) killable delay, rely on good will of (unkillable) neighbors and wait for them to release required memory. > > Again, not really sure what you mean > >> - mark the current task as cycled in #PF and somehow use this mark in allocator > > How? > >> - make sure that the current task is really cycled, have no progress, send him fatal signal to kill it and break the cycle. > > No! We cannot really kill the task if we could we would have done it by > the oom killer already > >> - implement any better ideas, >> - use any combination of previous points >> >> We can select required strategy for example via sysctl. > > Absolutely no! How can admin know any better than the kernel? > >> For me "random kill" is worst choice, >> Why can't we just kill the looped process instead? > > See above. > >> It can be marked as oom-unkillable, so OOM-killer was unable to select it. >> However I doubt it means "never kill it", for me it is something like "last possible victim" priority. > > It means never kill it because of OOM. If it is retrying because of OOM > then it is effectively the same thing. > > The oom killer from the #PF doesn't really provide any clear advantage > these days AFAIK. On the other hand it allows for a very disruptive > behavior. In a worst case it can lead to a system panic if the > VM_FAULT_OOM is not really caused by a memory shortage but rather a > wrong error handling. If a task is looping there without any progress > then it is still kilallable which is a much saner behavior IMHO. Let's continue this discussion in "Re: [PATCH memcg 3/3] memcg: handle memcg oom failures" thread. .
