Return-Path: Received: from caramon.arm.linux.org.uk ([78.32.30.218]:54630 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751357Ab1AES2c (ORCPT ); Wed, 5 Jan 2011 13:28:32 -0500 Date: Wed, 5 Jan 2011 18:27:54 +0000 From: Russell King - ARM Linux To: Trond Myklebust Cc: Marc Kleine-Budde , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , linux-nfs@vger.kernel.org, Linus Torvalds , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Marc Kleine-Budde Subject: Re: still nfs problems [Was: Linux 2.6.37-rc8] Message-ID: <20110105182753.GG8638@n2100.arm.linux.org.uk> References: <20110105110517.GQ25121@pengutronix.de> <20110105112701.GA8638@n2100.arm.linux.org.uk> <20110105134045.GS25121@pengutronix.de> <1294239193.3014.9.camel@heimdal.trondhjem.org> <4D2487CA.5040501@pengutronix.de> <1294240457.3014.13.camel@heimdal.trondhjem.org> <20110105155230.GC8638@n2100.arm.linux.org.uk> <1294247847.2998.23.camel@heimdal.trondhjem.org> <20110105172641.GF8638@n2100.arm.linux.org.uk> <1294251145.3574.16.camel@heimdal.trondhjem.org> Content-Type: text/plain; charset=us-ascii In-Reply-To: <1294251145.3574.16.camel@heimdal.trondhjem.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Wed, Jan 05, 2011 at 01:12:25PM -0500, Trond Myklebust wrote: > On Wed, 2011-01-05 at 17:26 +0000, Russell King - ARM Linux wrote: > > On Wed, Jan 05, 2011 at 12:17:27PM -0500, Trond Myklebust wrote: > > > We should already be flushing the kernel direct mapping after writing by > > > means of the calls to flush_dcache_page() in xdr_partial_copy_from_skb() > > > and all the helpers in net/sunrpc/xdr.c. > > > > Hmm, we're getting into the realms of what flush_dcache_page() is supposed > > to do and what it's not supposed to do. > > > > Is this page an associated with a mapping (iow, page_mapping(page) is non- > > NULL)? If not, flush_dcache_page() won't do anything, and from my > > understanding, its flush_anon_page() which you want to be using there > > instead. > > Actually, none of these pages are ever mapped into userspace, nor are > they mapped into the page cache. > > They are allocated directly using alloc_page() by the thread that called > the readdir() syscall, so afaics there should be no incoherent mappings > other than the kernel direct mapping and the one created by > vm_map_ram(). > > So, yes, you are right that we don't need the flush_dcache_page() here. I do still think you need _something_ there, otherwise data can remain in the direct map alias and not be visible via the vmap alias. I don't see that we have anything in place to handle this at present though. jejb mentioned something about making kunmap_atomic() always flush the cache, even for lowmem pages, but I think that's going to be exceedingly painful, to the extent that I believe it will prevent our PIO-only MMC drivers working - or we need a scatterlist API that will let drivers iterate over the scatterlist without needing to continually kmap_atomic and kunmap_atomic each page.