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

Soeren Moch
2013-01-14T11:59:21Z

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@web.de>
> Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Tested-by: Andrew Lunn <andrew@lunn.ch>
> Tested-by: Soeren Moch <smoch@web.de>

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).

As already reported earlier this patch improved the behavior compared to
linux-3.6.x and 3.7.0 (error after several ten minutes runtime), but
I still see a regression compared to linux-3.5.x. With this kernel the
same system with same workload runs flawlessly.

Regards,
Soeren