From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751532AbaEWIfL (ORCPT ); Fri, 23 May 2014 04:35:11 -0400 Received: from cantor2.suse.de ([195.135.220.15]:53895 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751867AbaEWIfB (ORCPT ); Fri, 23 May 2014 04:35:01 -0400 Message-ID: <537F082F.50501@suse.cz> Date: Fri, 23 May 2014 10:34:55 +0200 From: Vlastimil Babka User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Shawn Guo , Kevin Hilman , Andrew Morton CC: Joonsoo Kim , David Rientjes , Hugh Dickins , Greg Thelen , LKML , linux-mm@kvack.org, Minchan Kim , Mel Gorman , Bartlomiej Zolnierkiewicz , Michal Nazarewicz , Christoph Lameter , Rik van Riel , Olof Johansson , Stephen Warren , linux-arm-kernel Subject: Re: [PATCH v2] mm, compaction: properly signal and act upon lock and need_sched() contention References: <1399904111-23520-1-git-send-email-vbabka@suse.cz> <1400233673-11477-1-git-send-email-vbabka@suse.cz> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/23/2014 04:48 AM, Shawn Guo wrote: > On 23 May 2014 07:49, Kevin Hilman wrote: >> On Fri, May 16, 2014 at 2:47 AM, Vlastimil Babka wrote: >>> Compaction uses compact_checklock_irqsave() function to periodically check for >>> lock contention and need_resched() to either abort async compaction, or to >>> free the lock, schedule and retake the lock. When aborting, cc->contended is >>> set to signal the contended state to the caller. Two problems have been >>> identified in this mechanism. >> >> This patch (or later version) has hit next-20140522 (in the form >> commit 645ceea9331bfd851bc21eea456dda27862a10f4) and according to my >> bisect, appears to be the culprit of several boot failures on ARM >> platforms. > > On i.MX6 where CMA is enabled, the commit causes the drivers calling > dma_alloc_coherent() fail to probe. Tracing it a little bit, it seems > dma_alloc_from_contiguous() always return page as NULL after this > commit. > > Shawn > Really sorry, guys :/ -----8<----- From: Vlastimil Babka Date: Fri, 23 May 2014 10:18:56 +0200 Subject: mm-compaction-properly-signal-and-act-upon-lock-and-need_sched-contention-fix2 Step 1: Change function name and comment between v1 and v2 so that the return value signals the opposite thing. Step 2: Change the call sites to reflect the opposite return value. Step 3: ??? Step 4: Make a complete fool of yourself. Signed-off-by: Vlastimil Babka --- mm/compaction.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index a525cd4..5175019 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -237,13 +237,13 @@ static inline bool compact_should_abort(struct compact_control *cc) if (need_resched()) { if (cc->mode == MIGRATE_ASYNC) { cc->contended = true; - return false; + return true; } cond_resched(); } - return true; + return false; } /* Returns true if the page is within a block suitable for migration to */ -- 1.8.4.5