On Thu, 14 Jul 2016, Tetsuo Handa wrote: > Michal Hocko wrote: > > OK, this is the part I have missed. I didn't realize that the swapout > > path, which is indeed PF_MEMALLOC, can get down to blk code which uses > > mempools. A quick code travers shows that at least > > make_request_fn = blk_queue_bio > > blk_queue_bio > > get_request > > __get_request > > > > might do that. And in that case I agree that the above mentioned patch > > has unintentional side effects and should be re-evaluated. David, what > > do you think? An obvious fixup would be considering TIF_MEMDIE in > > mempool_alloc explicitly. > > TIF_MEMDIE is racy. Since the OOM killer sets TIF_MEMDIE on only one thread, > there is no guarantee that TIF_MEMDIE is set to the thread which is looping > inside mempool_alloc(). If the device mapper subsystem is not returning objects to the mempool, it should be investigated as a bug in the device mapper. There is no need to add workarounds to mempool_alloc to work around that bug. Mikulas > And since __GFP_NORETRY is used (regardless of > f9054c70d28bc214), out_of_memory() is not called via __alloc_pages_may_oom(). > This means that the thread which is looping inside mempool_alloc() can't > get TIF_MEMDIE unless TIF_MEMDIE is set by the OOM killer. > > Maybe set __GFP_NOMEMALLOC by default at mempool_alloc() and remove it > at mempool_alloc() when fatal_signal_pending() is true? But that behavior > can OOM-kill somebody else when current was not OOM-killed. Sigh... > > David Rientjes wrote: > > On Wed, 13 Jul 2016, Mikulas Patocka wrote: > > > > > What are the real problems that f9054c70d28bc214b2857cf8db8269f4f45a5e23 > > > tries to fix? > > > > > > > It prevents the whole system from livelocking due to an oom killed process > > stalling forever waiting for mempool_alloc() to return. No other threads > > may be oom killed while waiting for it to exit. > > Is that concern still valid? We have the OOM reaper for CONFIG_MMU=y case. > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
