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

[Sebastian Hesselbarth]

On 01/15/2013 05:56 PM, Jason Cooper wrote:
> Greg,
>
> I've added you to the this thread hoping for a little insight into USB
> drivers and their use of coherent and GFP_ATOMIC.  Am I barking up the
> wrong tree by looking a the drivers?
>
> On Mon, Jan 14, 2013 at 12:56:57PM +0100, Soeren Moch wrote:
> > On 20.11.2012 15:31, Marek Szyprowski wrote:
> > > dmapool always calls dma_alloc_coherent() with GFP_ATOMIC flag,
> > > regardless the flags provided by the caller. This causes excessive
> > > pruning of emergency memory pools without any good reason. Additionaly,
> > > on ARM architecture any driver which is using dmapools will sooner or
> > > later  trigger the following error:
> > > "ERROR: 256 KiB atomic DMA coherent pool is too small!
> > > Please increase it with coherent_pool= kernel parameter!".
> > > Increasing the coherent pool size usually doesn't help much and only
> > > delays such error, because all GFP_ATOMIC DMA allocations are always
> > > served from the special, very limited memory pool.
> > >
> > > This patch changes the dmapool code to correctly use gfp flags provided
> > > by the dmapool caller.
> > >
> > > Reported-by: Soeren Moch<smoch@xxxxxx>
> > > Reported-by: Thomas Petazzoni<thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Marek Szyprowski<m.szyprowski@xxxxxxxxxxx>
> > > Tested-by: Andrew Lunn<andrew@xxxxxxx>
> > > Tested-by: Soeren Moch<smoch@xxxxxx>
> >
> > Now I tested linux-3.7.1 (this patch is included there) on my Marvell
> > Kirkwood system. I still see
> >
> >    ERROR: 1024 KiB atomic DMA coherent pool is too small!
> >    Please increase it with coherent_pool= kernel parameter!
> >
> > after several hours of runtime under heavy load with SATA and
> > DVB-Sticks (em28xx / drxk and dib0700).
>
> Could you try running the system w/o the em28xx stick and see how it
> goes with v3.7.1?

Jason,

can you point out what you think we should be looking for?

I grep'd for 'GFP_' in  drivers/media/usb and especially for dvb-usb
(dib0700) it looks like most of the buffers in usb-urb.c are allocated
GFP_ATOMIC. em28xx also allocates some of the buffers atomic.

If we look for a mem leak in one of the above drivers (including sata_mv),
is there an easy way to keep track of allocated and freed kernel memory?

Sebastian
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