From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: [dm-devel] [PATCH 02/13] dm: kill dm_rq_bio_destructor Date: Fri, 18 May 2012 11:50:27 -0700 Message-ID: <20120518185027.GA9673@google.com> References: <20120518155729.GB19388@google.com> <20120518164319.GJ29330@agk-dp.fab.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Tejun Heo , axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org, dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, agk-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Junichi Nomura , Mikulas Patocka Return-path: Content-Disposition: inline In-Reply-To: <20120518164319.GJ29330-FDJ95KluN3Z0klwcnFlA1dvLeJWuRmrY@public.gmane.org> Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Fri, May 18, 2012 at 05:43:19PM +0100, Alasdair G Kergon wrote: > On Fri, May 18, 2012 at 08:57:29AM -0700, Tejun Heo wrote: > > Please explain why this is done and how it's safe. Alasdair / dm > > folks, can you please ack this? > > I think it's relying on there being never more than one reference on those > bios so that that endio fn, called exactly once, always frees it and there > are no dm_puts elsewhere. Is that a safe assumption? From my perusal of the code it certainly looks like it should be, but I don't know dm all that well. Seems like it might be better to use bio set's front_pad to put it in the same allocation as the bio, but I don't really want to get into that myself.