linux-kernel - Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc

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Date:	Tue, 15 Jan 2013 21:40:14 -0500
From:	Jason Cooper <jason@...edaemon.net>
To:	Soeren Moch <smoch@....de>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>, Arnd Bergmann <arnd@...db.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	linux-mm@...ck.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linaro-mm-sig@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v2] mm: dmapool: use provided gfp flags for all
 dma_alloc_coherent() calls

Soeren,

On Wed, Jan 16, 2013 at 01:17:59AM +0100, Soeren Moch wrote:
> On 15.01.2013 22:56, Jason Cooper wrote:
> >On Tue, Jan 15, 2013 at 03:16:17PM -0500, Jason Cooper wrote:
> >>If my understanding is correct, one of the drivers (most likely one)
> >>either asks for too small of a dma buffer, or is not properly
> >>deallocating blocks from the per-device pool.  Either case leads to
> >>exhaustion, and falling back to the atomic pool.  Which subsequently
> >>gets wiped out as well.
> >
> >If my hunch is right, could you please try each of the three dvb drivers
> >in turn and see which one (or more than one) causes the error?
> 
> In fact I use only 2 types of DVB sticks: em28xx usb bridge plus drxk
> demodulator, and dib0700 usb bridge plus dib7000p demod.
> 
> I would bet for em28xx causing the error, but this is not thoroughly
> tested. Unfortunately testing with removed sticks is not easy, because
> this is a production system and disabling some services for the long
> time we need to trigger this error will certainly result in unhappy
> users.

Just out of curiosity, what board is it?

> I will see what I can do here. Is there an easy way to track the buffer
> usage without having to wait for complete exhaustion?

DMA_API_DEBUG

> In linux-3.5.x there is no such problem. Can we use all available memory
> for dma buffers here on armv5 architectures, in contrast to newer
> kernels?

Were the loads exactly the same when you tested 3.5.x?  I looked at the
changes from v3.5 to v3.7.1 for all four drivers you mentioned as well
as sata_mv.

The biggest thing I see is that all of the media drivers got shuffled
around into their own subdirectories after v3.5.  'git show -M 0c0d06c'
shows it was a clean copy of all the files.

What would be most helpful is if you could do a git bisect between
v3.5.x (working) and the oldest version where you know it started
failing (v3.7.1 or earlier if you know it).

thx,

Jason.
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