linux-kernel - Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc

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Date:	Sat, 19 Jan 2013 16:29:49 +0100
From:	Soeren Moch <smoch@....de>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Jason Cooper <jason@...edaemon.net>,
	Greg KH <gregkh@...uxfoundation.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	linux-mm@...ck.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linaro-mm-sig@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc_coherent()
 calls

On 17.01.2013 21:26, Arnd Bergmann wrote:
> On Thursday 17 January 2013, Soeren Moch wrote:
>> On 17.01.2013 11:49, Arnd Bergmann wrote:
>>> On Wednesday 16 January 2013, Soeren Moch wrote:
>>>>>> 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.
>>>>>
>>>
>>> Any success with this? It should at least tell you if there is a
>>> memory leak in one of the drivers.
>>
>> Not yet, sorry. I have to do all the tests in my limited spare time.
>> Can you tell me what to search for in the debug output?
>
> Actually now that I've looked closer, you can't immediately see
> all the mappings as I thought.
>
> But please try enabling DMA_API_DEBUG in combination with this
> one-line patch:
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 6b2fb87..3df74ac 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -497,6 +497,7 @@ static void *__alloc_from_pool(size_t size, struct page **ret_page)
>   		pr_err_once("ERROR: %u KiB atomic DMA coherent pool is too small!\n"
>   			    "Please increase it with coherent_pool= kernel parameter!\n",
>   			    (unsigned)pool->size / 1024);
> +		debug_dma_dump_mappings(NULL);
>   	}
>   	spin_unlock_irqrestore(&pool->lock, flags);
>
> That will show every single allocation that is currently active. This lets
> you see where all the memory went, and if there is a possible leak or
> excessive fragmentation.
>
> 	Arnd
>

Please find attached a debug log generated with your patch.

I used the sata disk and two em28xx dvb sticks, no other usb devices,
no ethernet cable connected, tuners on saa716x-based card not used.

What I can see in the log: a lot of coherent mappings from sata_mv and 
orion_ehci, a few from mv643xx_eth, no other coherent mappings.
All coherent mappings are page aligned, some of them (from orion_ehci)
are not really small (as claimed in __alloc_from_pool).

I don't believe in a memory leak. When I restart vdr (the application
utilizing the dvb sticks) then there is enough dma memory available
again.

Regards,
Soeren



View attachment "dma_debug.log" of type "text/x-log" (215198 bytes)