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

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Date:	Thu, 23 Aug 2012 09:52:07 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	'Hiroshi Doyu' <hdoyu@...dia.com>
Cc:	pullip.cho@...sung.com, 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

Hi Hiroshi,

On Thursday, August 23, 2012 8:15 AM Hiroshi Doyu wrote:

> On Thu, 23 Aug 2012 07:58:34 +0200
> Marek Szyprowski <m.szyprowski@...sung.com> wrote:
> 
> > 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.
> 
> Ok, I've already sent v2 just now, where, instead of changing it back,
> just with GFP_ATOMIC, kzalloc() would be selected, just in case. I guess
> that this would be ok(a bit safer?)

I've posted some comments to v2. If you agree with my suggestion, no changes around
those vmalloc() calls will be needed.

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



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