linux-kernel - Re: [PATCH 0/5] fix exhaustion of ZONE

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Date:	Mon, 8 Sep 2008 14:00:17 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	tony.luck@...el.com, linux-ia64@...r.kernel.org,
	iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 0/5] fix exhaustion of ZONE_DMA with swiotlb (in x86 tree)

On Mon, Sep 08, 2008 at 06:10:09PM +0900, FUJITA Tomonori wrote:
> This patchset (against tip/master) fixes the problem that swiotlb
> exhausts ZONE_DMA:
> 
> http://lkml.org/lkml/2008/8/31/16
> 
> The root problem is that swiotlb_alloc_coherent always use ZONE_DMA,
> which is fine for IA64 but not for x86_64.
> 
> This patchset makes the callers set up the gfp flags so that
> swiotlb_alloc_coherent can stop playing with the gfp flags.
> 
> I think that it would be better to remove the allocation code in
> swiotlb_alloc_coherent theoretically (what swiotlb should do is taking
> care of the swiotlb memory. And swiotlb_alloc_coherent is not useful
> since we use it only when we can't allocate memory reachable by the
> device or we are in out of memory). But that code works for both x86
> and IA64 so it's not so bad, I guess.
> 
> #1 is for IA64, #2-4 for x86, and #5 is for swiotlb.

Cool :-)

This is much better than our last two tries to solve this problem. Doing
no gfp handling at all in swiotlb_alloc_coherent is a nice and clean
solution.

Joerg

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