From mboxrd@z Thu Jan 1 00:00:00 1970 From: MinChan Kim Subject: Re: [PATCH] Remove needless flush_dcache_page call Date: Fri, 16 Jan 2009 15:16:57 +0900 Message-ID: <20090116061657.GC6515@barrios-desktop> References: <20090116052804.GA18737@barrios-desktop> <20090116053338.GC31013@parisc-linux.org> <20090116055119.GA6515@barrios-desktop> <20090116055729.GF31013@parisc-linux.org> <20090116060830.GB6515@barrios-desktop> <20090116061341.GB22810@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Matthew Wilcox , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org To: Nick Piggin Return-path: Content-Disposition: inline In-Reply-To: <20090116061341.GB22810@wotan.suse.de> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Fri, Jan 16, 2009 at 07:13:41AM +0100, Nick Piggin wrote: > On Fri, Jan 16, 2009 at 03:08:30PM +0900, MinChan Kim wrote: > > On Thu, Jan 15, 2009 at 10:57:30PM -0700, Matthew Wilcox wrote: > > > Most I/O devices will do DMA to the page in question and thus the kernel > > > hasn't written to it and the CPU won't have the data in cache. For the > > > few devices which can't do DMA, it's the responsibility of the device > > > driver to call flush_dcache_page() (or some other flushing primitive). > > > > Hmm.. Now I am confusing. > > If devicer driver or with DMA makes sure cache consistency, > > Why filesystem code have to handle it ? > > Because the filesystem is accessing the page directly rathe rthan going to > IO. > > Basically, whoever reads or writes the page is responsible to avoid user > aliases. You see these calls in the VM for anonymous pages, in bounce > buffer layers, in filesystems that read or write from pages that are > exposed to userspace (ie. metadata generally need not be flushed because > it will not be mmapped by userspace). Totally, understand. Thanks for kind answering to my poor question in patience. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org