From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757703AbZEMOaj (ORCPT ); Wed, 13 May 2009 10:30:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754929AbZEMOaa (ORCPT ); Wed, 13 May 2009 10:30:30 -0400 Received: from charybdis-ext.suse.de ([195.135.221.2]:33582 "EHLO emea5-mh.id5.novell.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754301AbZEMOaa (ORCPT ); Wed, 13 May 2009 10:30:30 -0400 Subject: Re: do we really want to export more pdflush details in sysctls From: "Peter W. Morreale" To: Jens Axboe Cc: Christoph Hellwig , torvalds@osdl.org, akpm@osdl.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org In-Reply-To: <20090513130811.GE4140@kernel.dk> References: <20090513130128.GA10382@lst.de> <20090513130811.GE4140@kernel.dk> Content-Type: text/plain Organization: Linux Solutions Group Date: Wed, 13 May 2009 08:30:24 -0600 Message-Id: <1242225024.19182.174.camel@hermosa> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2009-05-13 at 15:08 +0200, Jens Axboe wrote: > On Wed, May 13 2009, Christoph Hellwig wrote: > > Hi all, > > > > commit fafd688e4c0c34da0f3de909881117d374e4c7af titled > > "mm: add /proc controls for pdflush threads" adds two more sysctl > > variables exposing details about pdflush threads. At the same time > > Jens Axboe is working on the per-bdi writeback patchset which will > > hopefull soon get rid of the pdflush threads in their current form. > > > > Is it really a good idea to expose more details now or should we revert > > this patch before 2.6.30 is out? > > Pained me as well when updating the patchset. I see little value in > these knobs as it is, I'm imagining that the submitter must have had a > use case where it made some difference? > No, I didn't. The rational was as explained in the commit log, merely that one size (eg: 2-8 threads) didn't fit all cases, so give the admin a chance at tuning w/o having to recompile. More importantly, I didn't know that Jens was working on significant changes to writeback. This is sorely needed as from what I see in the code, writeback is very unfair to 'fast' block devices (when both 'fast' and 'slow' devices co-exist), and consequently, the apps that reference them. Jens: When do you expect to complete the per-bdi patchset? In any event, it is not a good idea to expose knobs that will soon be obviated so please pull the patch. Thanks, -PWM