From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751837AbcF2WnS (ORCPT ); Wed, 29 Jun 2016 18:43:18 -0400 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:52708 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751480AbcF2WnQ (ORCPT ); Wed, 29 Jun 2016 18:43:16 -0400 X-Sasl-enc: Li3wHDSKqPt3UZXVlUgHnIgcyK8YPpVky3HhhCkU9S27 1467239815 Date: Wed, 29 Jun 2016 15:37:00 -0700 From: Greg KH To: David Rientjes Cc: Joonsoo Kim , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, hughd@google.com, mgorman@techsingularity.net, minchan@kernel.org, stable@vger.kernel.org, vbabka@suse.cz Subject: Re: [patch for-4.7] mm, compaction: prevent VM_BUG_ON when terminating freeing scanner Message-ID: <20160629223700.GA26264@kroah.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 29, 2016 at 02:47:20PM -0700, David Rientjes wrote: > It's possible to isolate some freepages in a pageblock and then fail > split_free_page() due to the low watermark check. In this case, we hit > VM_BUG_ON() because the freeing scanner terminated early without a > contended lock or enough freepages. > > This should never have been a VM_BUG_ON() since it's not a fatal > condition. It should have been a VM_WARN_ON() at best, or even handled > gracefully. > > Regardless, we need to terminate anytime the full pageblock scan was not > done. The logic belongs in isolate_freepages_block(), so handle its state > gracefully by terminating the pageblock loop and making a note to restart > at the same pageblock next time since it was not possible to complete the > scan this time. > > Reported-by: Minchan Kim > Signed-off-by: David Rientjes > --- > Note: I really dislike the low watermark check in split_free_page() and > consider it poor software engineering. The function should split a free > page, nothing more. Terminating memory compaction because of a low > watermark check when we're simply trying to migrate memory seems like an > arbitrary heuristic. There was an objection to removing it in the first > proposed patch, but I think we should really consider removing that > check so this is simpler. > > mm/compaction.c | 37 +++++++++++++++---------------------- > 1 file changed, 15 insertions(+), 22 deletions(-) This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read Documentation/stable_kernel_rules.txt for how to do this properly.