From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 7B2D66B0044 for ; Fri, 16 Jan 2009 00:51:27 -0500 (EST) Received: by ti-out-0910.google.com with SMTP id j3so794514tid.8 for ; Thu, 15 Jan 2009 21:51:24 -0800 (PST) Date: Fri, 16 Jan 2009 14:51:19 +0900 From: MinChan Kim Subject: Re: [PATCH] Remove needless flush_dcache_page call Message-ID: <20090116055119.GA6515@barrios-desktop> References: <20090116052804.GA18737@barrios-desktop> <20090116053338.GC31013@parisc-linux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090116053338.GC31013@parisc-linux.org> Sender: owner-linux-mm@kvack.org To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, npiggin@suse.de, akpm@linux-foundation.org List-ID: On Thu, Jan 15, 2009 at 10:33:38PM -0700, Matthew Wilcox wrote: > On Fri, Jan 16, 2009 at 02:28:04PM +0900, MinChan Kim wrote: > > Now, Anyone don't maintain cramfs. > > I don't know who is maintain romfs. so I send this patch to linux-mm, > > lkml, linux-dev. > > > > I am not sure my thought is right. > > > > When readpage is called, page with argument in readpage is just new > > allocated because kernel can't find that page in page cache. > > > > At this time, any user process can't map the page to their address space. > > so, I think D-cache aliasing probelm never occur. > > > > It make sense ? > > Sorry, no. You have to call fluch_dcache_page() in two situations -- > when the kernel is going to read some data that userspace wrote, *and* > when userspace is going to read some data that the kernel wrote. From a > quick look at the patch, this seems to be the second case. The kernel > wrote data to a pagecache page, and userspace should be able to read it. > > To understand why this is necessary, consider a processor which is > virtually indexed and has a writeback cache. The kernel writes to a > page, then a user process reads from the same page through a different > address. The cache doesn't find the data the kernel wrote because it > has a different virtual index, so userspace reads stale data. I see. :) Thanks for quick reponse and good explaination. Hmm,.. one more question. I can't find flush_dcache_page call in mpage_readpage which is generic read function. In case of ext fs, it use mpage_readpage with readpage. who and where call flush_dcache_page in mpage_readpage call path? > > -- > Matthew Wilcox Intel Open Source Technology Centre > "Bill, look, we understand that you're interested in selling us this > operating system, but compare it to ours. We can't possibly take such > a retrograde step." -- 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