Michal Hocko wrote: > Tetsuo has properly noted that mmput slow path might get blocked waiting > for another party (e.g. exit_aio waits for an IO). If that happens the > oom_reaper would be put out of the way and will not be able to process > next oom victim. We should strive for making this context as reliable > and independent on other subsystems as much as possible. > > Introduce mmput_async which will perform the slow path from an async > (WQ) context. This will delay the operation but that shouldn't be a > problem because the oom_reaper has reclaimed the victim's address space > for most cases as much as possible and the remaining context shouldn't > bind too much memory anymore. The only exception is when mmap_sem > trylock has failed which shouldn't happen too often. > > The issue is only theoretical but not impossible. Just a random thought, but after this patch is applied, do we still need to use a dedicated kernel thread for OOM-reap operation? If I recall correctly, the reason we decided to use a dedicated kernel thread was that calling down_read(&mm->mmap_sem) / mmput() from the OOM killer context is unsafe due to dependency. By replacing mmput() with mmput_async(), since __oom_reap_task() will no longer do operations that might block, can't we try OOM-reap operation from current thread which called mark_oom_victim() or oom_scan_process_thread() ? I want to start waking up the OOM reaper whenever TIF_MEMDIE is set or found. Using a dedicated kernel thread is still better because memory allocation path already consumed a lot of kernel stack? But we don't need to give up OOM-reaping when kthread_run() failed. -- 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>