From mboxrd@z Thu Jan 1 00:00:00 1970 From: swarren@wwwdotorg.org (Stephen Warren) Date: Fri, 30 May 2014 10:59:03 -0600 Subject: [PATCH v2] mm, compaction: properly signal and act upon lock and need_sched() contention In-Reply-To: <537F082F.50501@suse.cz> References: <1399904111-23520-1-git-send-email-vbabka@suse.cz> <1400233673-11477-1-git-send-email-vbabka@suse.cz> <537F082F.50501@suse.cz> Message-ID: <5388B8D7.1020907@wwwdotorg.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 05/23/2014 02:34 AM, Vlastimil Babka wrote: > 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. Tested-by: Stephen Warren This fix doesn't seem to be in linux-next yet:-(