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Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: James Bottomley <James.Bottomley@SteelEye.com>
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Date: Tue, 17 Jul 2007 08:12:39 +1000
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Cc: Arnd Bergmann <arnd@arndb.de>, linux-scsi@vger.kernel.org,
	Linux Kernel Development <linux-kernel@vger.kernel.org>,
	Alessandro Rubini <rubini@vision.unipv.it>,
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	Paul Mackerras <paulus@samba.org>, Jens Axboe <jens.axboe@oracle.com>,
	Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
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On Mon, 2007-07-16 at 17:03 -0500, James Bottomley wrote:
> On Tue, 2007-07-17 at 07:49 +1000, Benjamin Herrenschmidt wrote:
> > > No ... that was the point of flush_kernel_dcache_page().  The page in
> > > question is page cache backed and contains user mappings.  However, the
> > > block layer has already done a flush_dcache_page() in get_user_pages()
> > > and the user shouldn't be touching memory under I/O (unless they want
> > > self induced aliasing problems) so we're free to assume all the user
> > > cachelines are purged, hence all we have to do is flush the kernel alias
> > > to bring the page up to date and make the users see it correctly.
> > 
> > The block layer will have done that even in the swap-out path ? (Just
> > asking... I'm not very familiar with the block layer)
> 
> Er ... not really, this is the I/O path for user initiated I/O.  The
> page out path, by definition, can't have any extant user mappings.  For
> page out, the relevant page is flushed before its mapping is detached,
> and then it can be paged to the backing store (or for anonymous pages to
> the swap device) when no mappings remain.

Ok, thanks.

Ben.