linux-kernel - Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

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Date:	Tue, 17 Jul 2007 08:12:39 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	James Bottomley <James.Bottomley@...elEye.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>, Arnd Bergmann <arnd@...db.de>,
	linux-scsi@...r.kernel.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Alessandro Rubini <rubini@...ion.unipv.it>,
	Linux/PPC Development <linuxppc-dev@...abs.org>,
	Paul Mackerras <paulus@...ba.org>,
	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

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.


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