Michal Hocko wrote: > On Tue 29-03-16 22:45:40, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > From: Michal Hocko <mhocko@xxxxxxxx> > > > > > > __alloc_pages_may_oom is the central place to decide when the > > > out_of_memory should be invoked. This is a good approach for most checks > > > there because they are page allocator specific and the allocation fails > > > right after. > > > > > > The notable exception is GFP_NOFS context which is faking > > > did_some_progress and keep the page allocator looping even though there > > > couldn't have been any progress from the OOM killer. This patch doesn't > > > change this behavior because we are not ready to allow those allocation > > > requests to fail yet. Instead __GFP_FS check is moved down to > > > out_of_memory and prevent from OOM victim selection there. There are > > > two reasons for that > > > - OOM notifiers might release some memory even from this context > > > as none of the registered notifier seems to be FS related > > > - this might help a dying thread to get an access to memory > > > reserves and move on which will make the behavior more > > > consistent with the case when the task gets killed from a > > > different context. > > > > Allowing !__GFP_FS allocations to get TIF_MEMDIE by calling the shortcuts in > > out_of_memory() would be fine. But I don't like the direction you want to go. > > > > I don't like failing !__GFP_FS allocations without selecting OOM victim > > ( http://lkml.kernel.org/r/201603252054.ADH30264.OJQFFLMOHFSOVt@xxxxxxxxxxxxxxxxxxx ). > > I didn't get to read and digest that email yet but from a quick glance > it doesn't seem to be directly related to this patch. Even if we decide > that __GFP_FS vs. OOM killer logic is flawed for some reason then would > build on top as granting the access to memory reserves is not against > it. > I think that removing these shortcuts is better. > > Also, I suggested removing all shortcuts by setting TIF_MEMDIE from oom_kill_process() > > ( http://lkml.kernel.org/r/1458529634-5951-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx ). > > I personally do not like this much. I believe we have already tried to > explain why we have (some of) those shortcuts. They might be too > optimistic and there is a room for improvements for sure but I am not > convinced we can get rid of them that easily. These shortcuts are too optimistic. They assume that the target thread can call exit_oom_victim() but the reality is that the target task can get stuck at down_read(&mm->mmap_sem) in exit_mm(). If SIGKILL were sent to all thread groups sharing that mm, the possibility of the target thread getting stuck at down_read(&mm->mmap_sem) in exit_mm() is significantly reduced. http://lkml.kernel.org/r/20160329141442.GD4466@xxxxxxxxxxxxxx tried to let the OOM reaper to call exit_oom_victim() on behalf of the target thread by waking up the OOM reaper. But the OOM reaper won't call exit_oom_victim() because the OOM reaper will fail to reap memory because some thread sharing that mm and holding mm->mmap_sem for write will not receive SIGKILL if we use these shortcuts. As far as I know, all existing explanations for why we have these shortcuts are ignoring the possibility of such some thread. -- 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>