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

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Message-ID: <50FFF5C0.60000@web.de>
Date:	Wed, 23 Jan 2013 15:37:52 +0100
From:	Soeren Moch <smoch@....de>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Jason Cooper <jason@...edaemon.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	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 22.01.2013 19:13, Arnd Bergmann wrote:
> On Monday 21 January 2013, Greg KH wrote:
>>>
>>> I don't know a lot about USB, but I always assumed that this was not
>>> a normal condition and that there are only a couple of URBs per endpoint
>>> used at a time. Maybe Greg or someone else with a USB background can
>>> shed some light on this.
>>
>> There's no restriction on how many URBs a driver can have outstanding at
>> once, and if you have a system with a lot of USB devices running at the
>> same time, there could be lots of URBs in flight depending on the number
>> of host controllers and devices and drivers being used.

I only use one host controller and (in this test) two usb devices with
the same driver.

> Ok, thanks for clarifying that. I read some more of the em28xx driver,
> and while it does have a bunch of URBs in flight, there are only five
> audio and five video URBs that I see simultaneously being submitted,
> and then resubmitted from their completion handlers. I think this
> means that there should be 10 URBs active at any given time in this
> driver, which does not explain why we get 256 allocations.

I think the audio part of the em28xx bridge is not used in my DVB tests.

Are there other allocations from orion-ehci directly? Maybe something
special for isochronous transfers (since there is no problem with my 
other dvb sticks using bulk transfers)?

> I also noticed that the initial submissions are all atomic but don't
> need to, so it may be worth trying the patch below, which should also
> help in low-memory situations. We could also try moving the resubmission
> into a workqueue in order to let those be GFP_KERNEL, but I don't think
> that will help.

I built a linux-3.7.4 with the em28xx patch and both of your dma-mapping.c
patches. I still see the
   ERROR: 1024 KiB atomic DMA coherent pool is too small!

Soeren

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