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

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Date:	Thu, 17 Jan 2013 20:26:45 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Soeren Moch <smoch@....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 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
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