Subject: Re: still nfs problems [Was: Linux 2.6.37-rc8]
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        Uwe =?ISO-8859-1?Q?Kleine-K=F6nig?=
	<u.kleine-koenig@pengutronix.de>,
        Marc Kleine-Budde <m.kleine-budde@pengutronix.de>,
        linux-arm-kernel@lists.infradead.org,
        Parisc List <linux-parisc@vger.kernel.org>, linux-arch@vger.kernel.org
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Date: Wed, 05 Jan 2011 16:16:48 -0500
Message-ID: <1294262208.2952.4.camel@heimdal.trondhjem.org>
Sender: linux-nfs-owner@vger.kernel.org
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On Wed, 2011-01-05 at 13:08 -0800, Linus Torvalds wrote: 
> On Wed, Jan 5, 2011 at 1:04 PM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > On Wed, Jan 05, 2011 at 12:48:32PM -0800, Linus Torvalds wrote:
> >> (You can also force the problem with vmalloc() an then following the
> >> kernel page tables, but I hope nobody does that any more. I suspect
> >> I'm wrong, though, there's probably code that mixes vmalloc and
> >> physical page accesses in various drivers)
> >
> > Should vmalloc_to_page() (84 users)/vmalloc_to_pfn() (17 users) be
> > deprecated then? ;)
> 
> I do think that the "modern" way of doing it is
> "vmap()"/"vm_map_ram()" and friends, and it should be preferred over
> using vmalloc() and then looking up the pages.
> 
> But in the end, the two approaches really are equivalent, so it's not
> like it really matters. So I don't think we need to deprecate things
> officially, but obviously we should make people more aware of the
> whole virtual alias thing that crops up whenever you use any of these
> approaches.

So what should be the preferred way to ensure data gets flushed when
you've written directly to a page, and then want to read through the
vm_map_ram() virtual range? Should we be adding new semantics to
flush_kernel_dcache_page()?

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com