Re: [PATCH] Revert "mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE"

From: Michal Hocko <mhocko@kernel.org>
To: "Joonsoo Kim" <iamjoonsoo.kim@lge.com>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
	Tony Lindgren <tony@atomide.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Laura Abbott <lauraa@codeaurora.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Michal Nazarewicz <mina86@mina86.com>,
	Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>,
	Russell King <linux@armlinux.org.uk>,
	Will Deacon <will.deacon@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Revert "mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE"
Date: Thu, 17 May 2018 19:08:16 +0200	[thread overview]
Message-ID: <20180517170816.GW12670@dhcp22.suse.cz> (raw)
In-Reply-To: <20180517164947.GV12670@dhcp22.suse.cz>

On Thu 17-05-18 18:49:47, Michal Hocko wrote:
> On Thu 17-05-18 16:58:32, Ville Syrjälä wrote:
> > On Thu, May 17, 2018 at 04:36:29PM +0300, Ville Syrjälä wrote:
> > > On Thu, May 17, 2018 at 03:21:09PM +0200, Michal Hocko wrote:
> > > > On Thu 17-05-18 15:59:59, Ville Syrjala wrote:
> > > > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > > 
> > > > > This reverts commit bad8c6c0b1144694ecb0bc5629ede9b8b578b86e.
> > > > > 
> > > > > Make x86 with HIGHMEM=y and CMA=y boot again.
> > > > 
> > > > Is there any bug report with some more details? It is much more
> > > > preferable to fix the issue rather than to revert the whole thing
> > > > right away.
> > > 
> > > The machine I have in front of me right now didn't give me anything.
> > > Black screen, and netconsole was silent. No serial port on this
> > > machine unfortunately.
> > 
> > Booted on another machine with serial:
> 
> Could you provide your .config please?
> 
> [...]
> > [    0.000000] cma: Reserved 4 MiB at 0x0000000037000000
> [...]
> > [    0.000000] BUG: Bad page state in process swapper  pfn:377fe
> > [    0.000000] page:f53effc0 count:0 mapcount:-127 mapping:00000000 index:0x0
> 
> OK, so this looks the be the source of the problem. -128 would be a
> buddy page but I do not see anything that would set the counter to -127
> and the real map count updates shouldn't really happen that early.
> 
> Maybe CONFIG_DEBUG_VM and CONFIG_DEBUG_HIGHMEM will tell us more.

Looking closer, I _think_ that the bug is in set_highmem_pages_init->is_highmem
and zone_movable_is_highmem might force CMA pages in the zone movable to
be initialized as highmem. And that sounds supicious to me. Joonsoo?
-- 
Michal Hocko
SUSE Labs