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

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Message-ID: <50F5F1B7.3040201@web.de>
Date:	Wed, 16 Jan 2013 01:17:59 +0100
From:	Soeren Moch <smoch@....de>
To:	Jason Cooper <jason@...edaemon.net>
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

On 15.01.2013 22:56, Jason Cooper wrote:
> Soeren,
>
> 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.

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?

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?

Regards,
Soeren

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