Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 15 Dec 2000 06:26:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 15 Dec 2000 06:26:03 -0500 Received: from zeus.kernel.org ([209.10.41.242]:18698 "EHLO zeus.kernel.org") by vger.kernel.org with ESMTP id ; Fri, 15 Dec 2000 06:25:53 -0500 Date: Fri, 15 Dec 2000 10:51:48 +0000 From: "Stephen C. Tweedie" To: Alexander Viro Cc: Linus Torvalds , "Stephen C. Tweedie" , Russell Cattelan , linux-kernel@vger.kernel.org Subject: Re: Test12 ll_rw_block error. Message-ID: <20001215105148.E11931@redhat.com> In-Reply-To:

Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2i In-Reply-To: ; from viro@math.psu.edu on Fri, Dec 15, 2000 at 02:00:19AM -0500 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Fri, Dec 15, 2000 at 02:00:19AM -0500, Alexander Viro wrote: > On Thu, 14 Dec 2000, Linus Torvalds wrote: > > Just one: any fs that really cares about completion callback is very likely > to be picky about the requests ordering. So sync_buffers() is very unlikely > to be useful anyway. > > In that sense we really don't have anonymous buffers here. I seriously > suspect that "unrealistic" assumption is not unrealistic at all. I'm > not sufficiently familiar with XFS code to say for sure, but... Right. ext3 and reiserfs just want to submit their own IOs when it comes to the journal. (At least in ext3, already-journaled buffers can be written back by the VM freely.) It's a matter of telling the fs when that should start. > What we really need is a way for VFS/VM to pass the pressure on filesystem. > That's it. If fs wants unusual completions for requests - let it have its > own queueing mechanism and submit these requests when it finds that convenient. There is a very clean way of doing this with address spaces. It's something I would like to see done properly for 2.5: eliminate all knowledge of buffer_heads from the VM layer. It would be pretty simple to remove page->buffers completely and replace it with a page->private pointer, owned by whatever address_space controlled the page. Instead of trying to unmap and flush buffers on the page directly, these operations would become address_space operations. We could still provide the standard try_to_free_buffers() and unmap_underlying_metadata() functions to operate on the per-page buffer_head lists, and existing filesystems would only have to point their address_space "private metadata" operations at the generic functions. However, a filesystem which had additional ordering constraints could then intercept the flush or writeback calls from the VM and decide on its own how best to honour the VM pressure. This even works both for hashed and unhashed anonymous buffers, *if* you allow the filesystem to attach all of its hashed buffers buffers to an address_space of its own rather than having the buffer cache pool all such buffers together. --Stephen - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/