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

Soeren Moch
2013-01-16T08:56:22Z

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?)

> 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