Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc_coherent() calls

Soeren Moch
2013-01-16T17:32:26Z

On 16.01.2013 09:55, Soeren Moch wrote:
> On 16.01.2013 04:24, Soeren Moch wrote:
>> On 16.01.2013 03:40, Jason Cooper wrote:
>>> 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.
>>>
> OK, I could trigger the error
> ERROR: 1024 KiB atomic DMA coherent pool is too small!
> Please increase it with coherent_pool= kernel parameter!
> only with em28xx sticks and sata, dib0700 sticks removed.
>
>>> Just out of curiosity, what board is it?
>>
>> The kirkwood board? A modified Guruplug Server Plus.
> em28xx sticks: "TerraTec Cinergy HTC Stick HD" and "PCTV Quatro Stick"
> dib0700 sticks: "WinTV-NOVA-TD Stick"
>>>
>>>> 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
>>
>> OK, maybe I can try this.
>>>
>>>> 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?
>>
>> Exactly the same, yes.
>>
>>> 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).
>>>
>> I did not bisect it, but Marek mentioned earlier that commit
>> e9da6e9905e639b0f842a244bc770b48ad0523e9 in Linux v3.6-rc1 introduced
>> new code for dma allocations. This is probably the root cause for the
>> new (mis-)behavior (due to my tests 3.6.0 is not working anymore).
>
> I don't want to say that Mareks patch is wrong, probably it triggers a
> bug somewhere else! (in em28xx?)

The em28xx sticks are using isochronous usb transfers. Is there a
special handling for that?

>> I'm not very familiar with arm mm code, and from the patch itself I
>> cannot understand what's different. Maybe CONFIG_CMA is default
>> also for armv5 (not only v6) now? But I might be totally wrong here,
>> maybe someone of the mm experts can explain the difference?
>>
Regards,
Soeren