linux-kernel - RE: [RFC 2/4] ARM: dma-mapping: IOMMU allocates pages from pool with GFP

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Message-id: <012401cd80f4$59727020$0c575060$%szyprowski@samsung.com>
Date:	Thu, 23 Aug 2012 07:58:34 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	'Hiroshi Doyu' <hdoyu@...dia.com>, pullip.cho@...sung.com
Cc:	linux-arm-kernel@...ts.infradead.org,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kyungmin.park@...sung.com,
	arnd@...db.de, linux@....linux.org.uk, chunsang.jeong@...aro.org,
	'Krishna Reddy' <vdumpa@...dia.com>, konrad.wilk@...cle.com,
	subashrp@...il.com, minchan@...nel.org
Subject: RE: [RFC 2/4] ARM: dma-mapping: IOMMU allocates pages from pool with
 GFP_ATOMIC

Hello,

On Wednesday, August 22, 2012 3:37 PM Hiroshi Doyu wrote:

> KyongHo Cho <pullip.cho@...sung.com> wrote @ Wed, 22 Aug 2012 14:47:00 +0200:
> 
> > vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic context.
> 
> Right.
> 
> I've been thinking that kzalloc() may be enough here, since
> vzalloc() was introduced to avoid allocation failure for big chunk of
> memory, but I think that it's unlikely that the number of page array
> can be so big. So I propose to drop vzalloc() here, and just simply to
> use kzalloc only as below(*1).

We already had a discussion about this, so I don't think it makes much sense to
change it back to kzalloc. This vmalloc() call won't hurt anyone. It should not
be considered a problem for atomic allocations, because no sane driver will try
to allocate buffers larger than a dozen KiB with GFP_ATOMIC flag. I would call
such try a serious bug, which we should not care here.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center



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