From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755475Ab0KUUQL (ORCPT ); Sun, 21 Nov 2010 15:16:11 -0500 Received: from element.ksp.sk ([158.195.16.154]:57859 "EHLO ksp.sk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753290Ab0KUUQK (ORCPT ); Sun, 21 Nov 2010 15:16:10 -0500 Message-ID: <4CE97E06.6000207@dcs.fmph.uniba.sk> Date: Sun, 21 Nov 2010 21:16:06 +0100 From: Richard Kralovic User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101030 Icedove/3.0.10 MIME-Version: 1.0 To: Jeff Moyer CC: linux-kernel@vger.kernel.org, axboe@kernel.dk Subject: Re: CFQ and dm-crypt References: <4CC439ED.8090400@dcs.fmph.uniba.sk> <4CD185C2.8000006@dcs.fmph.uniba.sk> In-Reply-To: X-Enigmail-Version: 1.0.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >> On 11/03/10 04:23, Jeff Moyer wrote: >>>>> CFQ io scheduler relies on using task_struct current to determine which >>>>> process makes the io request. On the other hand, some dm modules (such >>>>> as dm-crypt) use separate threads for doing io. As CFQ sees only these >>>>> threads, it provides a very poor performance in such a case. >>>>> >>>>> IMHO the correct solution for this would be to store, for every io >>>>> request, the process that initiated it (and preserve this information >>>>> while the request is processed by device mapper). Would that be feasible? >>> Sure. Try the attached patch (still an rfc) and let us know how it >>> goes. In my environment, it speed up multiple concurrent buffered >>> readers. I wasn't able to do a full analysis via blktrace as 2.6.37-rc1 >>> seems to have broken blktrace support on my system. >> >> Thanks for the patch. Unfortunately, I got a kernel panic quite soon >> after booting the patched kernel. I was not able to reproduce the >> panic in a virtual machine, so I had to manually note the backtrace, >> thus I apologize that it's incomplete: > > Hi, Richard, > > I have another patch for you to try. This one holds up pretty well in > my testing using a dm-crypt target. Without the patch, I see no > priority separation: Hello, I am sorry for a late reply (it took me some time to try the patch on my main machine). Thank you for your work; unfortunately, I'm still getting a panic at early boot stages: The BUG_ON assert in cfq-iosched.c:cic_free_func failed, with a call trace as follows: cfq_free_io_context put_io_context cfq_put_request elv_put_request blk_finish_request ... I applied your patch at Linus's git tree (commit b86db4744230c94e480de56f1b7f31117edbf193), it applied cleanly. I tried a little to find the source of the problem, but without success so far. However, I think that calling put_io_context in bio_endio only may introduce memory leaks under certain situations (although this is probably not related to the panic I get): In blk-core.c:blk_rq_prep_clone, __bio_clone allocates the io_context, but if subsequent allocations fail, bio_free in free_and_out does not free it. Similarly, in dm-crypt.c:crypt_alloc_buffer, bio_put does not free the io_context. Or have I misunderstood something? Greets Richard