From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752815AbdHOAVC (ORCPT ); Mon, 14 Aug 2017 20:21:02 -0400 Received: from mail-pg0-f43.google.com ([74.125.83.43]:33359 "EHLO mail-pg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752740AbdHOAVA (ORCPT ); Mon, 14 Aug 2017 20:21:00 -0400 Date: Mon, 14 Aug 2017 17:20:58 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Andrea Arcangeli cc: Michal Hocko , "Kirill A. Shutemov" , Andrew Morton , Tetsuo Handa , Oleg Nesterov , Hugh Dickins , linux-mm@kvack.org, LKML Subject: Re: [PATCH] mm, oom: allow oom reaper to race with exit_mmap In-Reply-To: <20170726162912.GA29716@redhat.com> Message-ID: References: <20170724141526.GM25221@dhcp22.suse.cz> <20170724145142.i5xqpie3joyxbnck@node.shutemov.name> <20170724161146.GQ25221@dhcp22.suse.cz> <20170725142626.GJ26723@dhcp22.suse.cz> <20170725151754.3txp44a2kbffsxdg@node.shutemov.name> <20170725152300.GM26723@dhcp22.suse.cz> <20170725153110.qzfz7wpnxkjwh5bc@node.shutemov.name> <20170725160359.GO26723@dhcp22.suse.cz> <20170725191952.GR29716@redhat.com> <20170726054557.GB960@dhcp22.suse.cz> <20170726162912.GA29716@redhat.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 26 Jul 2017, Andrea Arcangeli wrote: > From 3d9001490ee1a71f39c7bfaf19e96821f9d3ff16 Mon Sep 17 00:00:00 2001 > From: Andrea Arcangeli > 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 With your follow-up one liner to include linux/oom.h folded in: Tested-by: David Rientjes