On Wed, 26 Jul 2017, Andrea Arcangeli wrote: > From 3d9001490ee1a71f39c7bfaf19e96821f9d3ff16 Mon Sep 17 00:00:00 2001 > From: Andrea Arcangeli <aarcange@xxxxxxxxxx> > Date: Tue, 25 Jul 2017 20:02:27 +0200 > Subject: [PATCH 1/1] mm: oom: let oom_reap_task and exit_mmap to run > concurrently > > This is purely required because exit_aio() may block and exit_mmap() may > never start, if the oom_reap_task cannot start running on a mm with > mm_users == 0. > > At the same time if the OOM reaper doesn't wait at all for the memory > of the current OOM candidate to be freed by exit_mmap->unmap_vmas, it > would generate a spurious OOM kill. > > If it wasn't because of the exit_aio or similar blocking functions in > the last mmput, it would be enough to change the oom_reap_task() in > the case it finds mm_users == 0, to wait for a timeout or to wait for > __mmput to set MMF_OOM_SKIP itself, but it's not just exit_mmap the > problem here so the concurrency of exit_mmap and oom_reap_task is > apparently warranted. > > It's a non standard runtime, exit_mmap() runs without mmap_sem, and > oom_reap_task runs with the mmap_sem for reading as usual (kind of > MADV_DONTNEED). > > The race between the two is solved with a combination of > tsk_is_oom_victim() (serialized by task_lock) and MMF_OOM_SKIP > (serialized by a dummy down_write/up_write cycle on the same lines of > the ksm_exit method). > > If the oom_reap_task() may be running concurrently during exit_mmap, > exit_mmap will wait it to finish in down_write (before taking down mm > structures that would make the oom_reap_task fail with use after > free). > > If exit_mmap comes first, oom_reap_task() will skip the mm if > MMF_OOM_SKIP is already set and in turn all memory is already freed > and furthermore the mm data structures may already have been taken > down by free_pgtables. > > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> With your follow-up one liner to include linux/oom.h folded in: Tested-by: David Rientjes <rientjes@xxxxxxxxxx> -- 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>
