From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932498AbWJILlK (ORCPT ); Mon, 9 Oct 2006 07:41:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932515AbWJILlJ (ORCPT ); Mon, 9 Oct 2006 07:41:09 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.31.123]:58296 "EHLO atrey.karlin.mff.cuni.cz") by vger.kernel.org with ESMTP id S932498AbWJILlI (ORCPT ); Mon, 9 Oct 2006 07:41:08 -0400 Date: Mon, 9 Oct 2006 13:40:41 +0200 From: Jan Kara To: Andrew Morton Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/3] Fix IO error reporting on fsync() Message-ID: <20061009114040.GI17620@atrey.karlin.mff.cuni.cz> References: <20061006114947.GC14533@atrey.karlin.mff.cuni.cz> <20061006230609.c04e78bc.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061006230609.c04e78bc.akpm@osdl.org> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > On Fri, 6 Oct 2006 13:49:47 +0200 > Jan Kara wrote: > > > current code in buffer.c has two pitfalls that cause problems with IO > > error reporting of filesystems using mapping->private_list for their > > metadata buffers (e.g. ext2). > > The first problem is that end_io_async_write() does not mark IO error > > in the buffer flags, only in the page flags. Hence fsync_buffers_list() > > does not find out that some IO error has occured and will not report it. > > The second problem is that buffers from private_list can be freed > > (e.g. under memory pressure) and if fsync_buffer_list() is called after > > that moment, IO error is lost - note that metadata buffers mark AS_EIO > > on the *device mapping* not on the inode mapping. > > Following series of three patches tries to fix these problems. The > > approach I took (after some discussions with Andrew) is introducing > > dummy buffer_head in the mapping instead of private_list. This dummy > > buffer head serves as a head of metadata buffer list and also collects > > IO errors from other buffers on the list (see the third patch for more > > details). This is kind of compromise between introducing a pointer to > > inode's address_space into each buffer and between using list_head > > instead of buffer_head and playing some dirty tricks to recognize that > > one particular list_head is actually from address_space and not from > > buffer_head. Any suggestions for improvements welcome. > > This is really complex, and enlarges the inode by quite a lot, which hurts. I agree (at least with the second part ;). I can write a patch which keeps the inode size but the code will be uglier... Another possibility is to put there just a buffer_head pointer and allocate buffer head dynamically. That has an advantage that only filesystems using metadata_list has to bear the memory cost... > What about putting an address_space* into the buffer_head? Transfer the > EIO state into the address_space within, say, __remove_assoc_queue()? Yes, that's of course possible. But it enlarges each buffer head by 4 bytes (or 8 on 64-bit arch). Hmm, but you are right that on the systems I've looked at this would actually be less memory. OK, I'll write this version of the patch. Honza -- Jan Kara SuSE CR Labs