linux-kernel - Re: [PATCH v3] iommu/dma: Use NUMA aware memory allocations in __iommu_dma_alloc

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Date:   Wed, 21 Nov 2018 16:47:48 +0000
From:   John Garry <john.garry@...wei.com>
To:     Will Deacon <will.deacon@....com>
CC:     <joro@...tes.org>, <robin.murphy@....com>,
        <linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
        <ganapatrao.kulkarni@...ium.com>, <hch@....de>,
        <m.szyprowski@...sung.com>, <linuxarm@...wei.com>
Subject: Re: [PATCH v3] iommu/dma: Use NUMA aware memory allocations in
 __iommu_dma_alloc_pages()

On 21/11/2018 16:07, Will Deacon wrote:
> On Wed, Nov 21, 2018 at 10:54:10PM +0800, John Garry wrote:
>> From: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
>>
>> Change function __iommu_dma_alloc_pages() to allocate pages for DMA from
>> respective device NUMA node. The ternary operator which would be for
>> alloc_pages_node() is tidied along with this.
>>
>> We also include a change to use kvzalloc() for kzalloc()/vzalloc()
>> combination.
>>
>> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
>> [JPG: Added kvzalloc(), drop pages ** being device local, tidied ternary operator]
>> Signed-off-by: John Garry <john.garry@...wei.com>
>
> Weird, you're missing a diffstat here.
>
> Anyway, the patch looks fine to me, but it would be nice if you could
> justify the change with some numbers. Do you actually see an improvement
> from this change?
>

Hi Will,

Ah, I missed adding my comments explaining the motivation. It would be 
better in the commit log. Anyway, here's the snippet:

" ... as mentioned in [3], dma_alloc_coherent() uses the locality
information from the device - as in direct DMA - so this patch is just
applying this same policy.

[3] 
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1692998.html"

I did have some numbers to show improvement in some scenarios when I 
tested this a while back which I'll dig out.

However I would say that some scenarios will improve and the opposite 
for others with this change, considering different conditions in which 
DMA memory may be used.

Cheers,
John

> Will
>
> .
>