From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: [patch] fs: improved handling of page and buffer IO errors Date: Thu, 23 Oct 2008 07:48:04 -0600 Message-ID: <20081023134804.GL26094@parisc-linux.org> References: <20081021143518.GA7158@2ka.mipt.ru> <20081021145901.GA28279@fogou.chygwyn.com> <20081021162957.GQ26184@parisc-linux.org> <20081022124829.GA826@shareable.org> <20081022134531.GE26094@parisc-linux.org> <20081022143511.GF26094@parisc-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: jamie@shareable.org, steve@chygwyn.com, zbr@ioremap.net, npiggin@suse.de, akpm@linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org To: Miklos Szeredi Return-path: Received: from palinux.external.hp.com ([192.25.206.14]:43702 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750856AbYJWNsI (ORCPT ); Thu, 23 Oct 2008 09:48:08 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Oct 22, 2008 at 04:45:24PM +0200, Miklos Szeredi wrote: > On Wed, 22 Oct 2008, Matthew Wilcox wrote: > > remap_file_pages() only hurts if you map the same page more than once > > (which is permitted, but again, I don't think anyone actually does > > that). > > This is getting very offtopic... but remap_file_pages() is just like > MAP_FIXED, that the address at which a page is mapped is determined by > the caller, not the kernel. So coherency with other, independent > mapping of the file is basically up to chance. Oh, right, I see. > Do we care? I very much hope not. Why do PA-RISC and friends care at > all about mmap coherecy? Is it real-world problem driven or just to > be safe? One reason to care is performance. If two tasks have libc mapped coherently, then the addresses will collide in the cache and they'll use the same cachelines. I don't know how much applications care about correctness with mmap -- they certainly do with sysv shm. I probably knew about some applications that broke when I was working on this code -- back in 2002. -- 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."