From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [git patches] xfs and block fixes for virtually indexed arches Date: Fri, 18 Dec 2009 11:30:12 +0100 Message-ID: <1261132212.3013.45.camel@mulgrave.site> References: <1261120128.3013.8.camel@mulgrave.site> <20091218183353I.fujita.tomonori@lab.ntt.co.jp> <1261130489.3013.41.camel@mulgrave.site> <20091218192401D.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from cantor.suse.de ([195.135.220.2]:48239 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752100AbZLRKaS (ORCPT ); Fri, 18 Dec 2009 05:30:18 -0500 In-Reply-To: <20091218192401D.fujita.tomonori@lab.ntt.co.jp> Sender: linux-arch-owner@vger.kernel.org List-ID: To: FUJITA Tomonori Cc: jens.axboe@oracle.com, torvalds@linux-foundation.org, tytso@mit.edu, kyle@mcmartin.ca, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, hch@infradead.org, linux-arch@vger.kernel.org On Fri, 2009-12-18 at 19:24 +0900, FUJITA Tomonori wrote: > On Fri, 18 Dec 2009 11:01:29 +0100 > James Bottomley wrote: > > > > Yeah, but now only XFS passes vmap'ed pages to the block layer. Isn't > > > it better to wait until we have real users of the API? > > > > XFS is a real user ... the XFS filesystem is our most trusted code base > > that can break the 8TB limit, which hard disks are already at. Ext4 may > > be ready, but it's not universally present in enterprise distros like > > XFS. > > XFS already has the own code to handle that, which works fine (with > your patchset except for 5/6 for the block layer). Not much motivation > for XFS to move to the generic API? Right, but it's for completeness. If we decide to allow vmap buffers, then only supporting them on certain paths is a recipe for confusion in a year's time when someone assumes we support vmap buffers on all block paths; a bit like the current confusion over what we support .... > > > > That would ensure the architecturally > > > > correct flushing of the aliases, and would satisfy the expectations of > > > > blk_rq_map_kern(). The down side is that vmap/vmalloc set up and clear > > > > page tables, which isn't necessary and might impact performance (xfs > > > > people?) > > > > > > btw, I'm not sure that the existing blk_rq_map_* API isn't fit well to > > > file systems since blk_rq_map_user and blk_rq_map_kern takes a request > > > structure. > > > > OK, so that was illustrative. The meat of the change is at the bio > > layer anyway (fss tend to speak bios). > > Yeah, I think so, it's up to Jens to add new APIs for vmap there. Agreed. James