netdev - Re: [PATCH V2] net: ethernet: mellanox: correct page conversion

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Date:	Wed, 20 Apr 2016 14:08:22 +0300
From:	Eran Ben Elisha <eranlinuxmellanox@...il.com>
To:	Sinan Kaya <okaya@...eaurora.org>
Cc:	Christoph Hellwig <hch@...radead.org>, linux-rdma@...r.kernel.org,
	timur@...eaurora.org, cov@...eaurora.org,
	Yishai Hadas <yishaih@...lanox.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] net: ethernet: mellanox: correct page conversion

Hi Sinan,

We are working in Mellanox for a solution which
removes the vmap call and allocate contiguous memory (using dma_alloc_coherent).

Thanks,
Eran


On Tue, Apr 19, 2016 at 9:37 PM, Sinan Kaya <okaya@...eaurora.org> wrote:
> On 4/19/2016 2:22 PM, Christoph Hellwig wrote:
>> What I think we need is something like the patch below.  In the long
>> ru nwe should also kill the mlx4_buf structure which now is pretty
>> pointless.
>
> Maybe; this could be the correct approach if we can guarantee that the
> architecture can allocate the requested amount of memory with
> dma_alloc_coherent.
>
> When I brought this issue a year ago, the objection was that my code
> doesn't compile on intel (dma_to_phys) and also some arches run out of
> DMA memory with existing customer base.
>
> If there is a real need to maintain compatibility with the existing
> architectures due to limited amount of DMA memory, we need to correct this
> code to make proper use of vmap via alloc_pages and also insert the
> dma_sync in proper places for DMA API conformance.
>
> Also, the tx descriptors always has to be allocated from a single DMA region
> or the tx code needs to be corrected to support page_list.
>
> If we can live with just using dma_alloc_coherent, your solution is
> better. I was trying to put this support for 64bit arches only while
> maintaining support for the existing code base.
>
>>
>> ---
>> From a493881d2a6c90152d3daabb7b6b3afd1d254d78 Mon Sep 17 00:00:00 2001
>> From: Christoph Hellwig <hch@....de>
>> Date: Tue, 19 Apr 2016 14:12:14 -0400
>> Subject: mlx4_en: don't try to split and vmap dma coherent allocations
>>
>> The memory returned by dma_alloc_coherent is not suitable for calling
>> virt_to_page on it, as it might for example come from vmap allocator.
>>
>> Remove the code that calls virt_to_page and vmap on dma coherent
>> allocations from the mlx4 drivers, and replace them with a single
>> high-order dma_alloc_coherent call.
>>
>> Signed-off-by: Christoph Hellwig <hch@....de>
>> Reported-by: Sinan Kaya <okaya@...eaurora.org>
>
>
> --
> Sinan Kaya
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
> --
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