linux-kernel - Re: RFC: prepare for struct scatterlist entries without page backing

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Message-ID: <20150813143528.GC17183@lst.de>
Date:	Thu, 13 Aug 2015 16:35:28 +0200
From:	Christoph Hellwig <hch@....de>
To:	Julian Calaby <julian.calaby@...il.com>
Cc:	Boaz Harrosh <boaz@...xistor.com>, Christoph Hellwig <hch@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	axboe@...nel.dk, linux-mips@...ux-mips.org,
	linux-ia64@...r.kernel.org, linux-nvdimm@...1.01.org,
	David Howells <dhowells@...hat.com>,
	sparclinux <sparclinux@...r.kernel.org>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	linux-arch@...r.kernel.org, linux-s390@...r.kernel.org,
	x86@...nel.org, David Woodhouse <dwmw2@...radead.org>,
	Håvard Skinnemoen <hskinnemoen@...il.com>,
	linux-xtensa@...ux-xtensa.org, grundler@...isc-linux.org,
	realmz6@...il.com, alex.williamson@...hat.com,
	linux-metag@...r.kernel.org, Michal Simek <monstr@...str.eu>,
	linux-parisc@...r.kernel.org, vgupta@...opsys.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-alpha@...r.kernel.org,
	Linux Media Mailing List <linux-media@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: RFC: prepare for struct scatterlist entries without page
	backing

On Thu, Aug 13, 2015 at 09:37:37AM +1000, Julian Calaby wrote:
> I.e. ~90% of this patch set seems to be just mechanically dropping
> BUG_ON()s and converting open coded stuff to use accessor functions
> (which should be macros or get inlined, right?) - and the remaining
> bit is not flushing if we don't have a physical page somewhere.

Which is was 90%.  By lines changed most actually is the diffs for
the cache flushing.

> Would it make sense to split this patch set into a few bits: one to
> drop all the useless BUG_ON()s, one to convert all the open coded
> stuff to accessor functions, then another to do the actual page-less
> sg stuff?

Without the ifs the BUG_ON() actually are useful to assert we
never feed the sort of physical addresses we can't otherwise support,
so I don't think that part is doable.

A simple series to make more use of sg_phys and add sg_pfn might
still be useful, though.
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