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

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Message-ID: <20120823091519.804aeae4ba93bcfe011e787c@nvidia.com>
Date:	Thu, 23 Aug 2012 09:15:19 +0300
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
CC:	"pullip.cho@...sung.com" <pullip.cho@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kyungmin.park@...sung.com" <kyungmin.park@...sung.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"chunsang.jeong@...aro.org" <chunsang.jeong@...aro.org>,
	Krishna Reddy <vdumpa@...dia.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"subashrp@...il.com" <subashrp@...il.com>,
	"minchan@...nel.org" <minchan@...nel.org>
Subject: Re: [RFC 2/4] ARM: dma-mapping: IOMMU allocates pages from pool
 with GFP_ATOMIC

Hi,

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?)
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