On 04/14/2012 03:38 AM, Russell King - ARM Linux wrote:
On Fri, Apr 13, 2012 at 04:05:50PM +0200, Marek Szyprowski wrote:
This patch changes dma-mapping subsystem to use generic vmalloc areas for all consistent dma allocations. This increases the total size limit of the consistent allocations and removes platform hacks and a lot of duplicated code.
NAK. I don't think you appreciate the contexts from which the dma coherent code can be called from, and the reason why we pre-allocate the page tables (so that IRQ-based allocations work.)
The vmalloc region doesn't allow that because page tables are allocated using GFP_KERNEL not GFP_ATOMIC.
Sorry.
Off-topic.
I don't know why vmalloc functions have gfp_t argument. As Russel pointed out, we allocates page tables with GFP_KERNEL regardless of gfp_t passed. It means gfp_t passed is useless. I see there are many cases calling __vmalloc with GFP_NOFS, even GFP_ATOMIC. Then, it could end up deadlocking in reclaim context or schedule bug. I'm not sure why we can't see such bugs until now. If I didn't miss something, Shouldn't we fix it?
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