linux-kernel - Re: pci_map_sg() does not coalesce adjacent physical memory? x86

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Date:	Wed, 19 Nov 2008 10:45:09 +0100
From:	"Leon Woestenberg" <leon.woestenberg@...il.com>
To:	"FUJITA Tomonori" <fujita.tomonori@....ntt.co.jp>
Cc:	jens.axboe@...cle.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	James.Bottomley@...senpartnership.com, tj@...nel.org
Subject: Re: pci_map_sg() does not coalesce adjacent physical memory? x86

Hello,

On Wed, Nov 19, 2008 at 8:58 AM, FUJITA Tomonori
<fujita.tomonori@....ntt.co.jp> wrote:
> On Wed, 19 Nov 2008 15:58:12 +0900
> FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
>> On Wed, 19 Nov 2008 07:22:31 +0100
>
> - pci_map_sg/dma_map_sg are used with a scatter gather list that
> doesn't come from the block layer (e.g. some network drivers do).
>
This is the point I then want to make: we have pci_map_sg() users in
other system than the block layer, the network and v4l2 subsystems,
why cannot they benefit from coalescing?

Should they copy the block layer coalescing implementation, or should
that implementation be made more generic and live outside the block
sub system?

My intended use case is as follows. See the sg_write() call for the code flow.

http://www.sidebranch.com/leon/user_dma_sg.c


Thanks,
-- 
Leon
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