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

[Soeren Moch]

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.
>
> Just out of curiosity, what board is it?

The kirkwood board? A modified Guruplug Server Plus.
> > 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'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





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