linux-kernel - Re: [PATCH 31/31] dma-mapping-common: skip kmemleak checks for page-less SG entries

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Date:	Thu, 13 Aug 2015 16:33:25 +0200
From:	Christoph Hellwig <hch@....de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
	Dan Williams <dan.j.williams@...el.com>,
	Vineet Gupta <vgupta@...opsys.com>,
	Håvard Skinnemoen <hskinnemoen@...il.com>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	Miao Steven <realmz6@...il.com>,
	David Howells <dhowells@...hat.com>,
	Michal Simek <monstr@...str.eu>,
	the arch/x86 maintainers <x86@...nel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	grundler@...isc-linux.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	linux-alpha@...r.kernel.org,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	linux-metag@...r.kernel.org,
	linux-mips <linux-mips@...ux-mips.org>,
	Parisc List <linux-parisc@...r.kernel.org>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	linux-s390 <linux-s390@...r.kernel.org>,
	sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>,
	Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [PATCH 31/31] dma-mapping-common: skip kmemleak checks for
	page-less SG entries

On Wed, Aug 12, 2015 at 09:05:15AM -0700, Linus Torvalds wrote:
> [ Again, I'm responding to one random patch - this pattern was in
> other patches too.  ]
> 
> A question: do we actually expect to mix page-less and pageful SG
> entries in the same SG list?
> 
> How does that happen?

Both for DAX and the video buffer case people could do direct I/O
spanning the boundary between such a VMA and a normal one unless
we add special code to prevent that.  Right now I don't think it's
all that useful, but then again it doesn't seem harmful either
and adding those checks might add up.
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