From: Chris Mason Subject: Re: [PATCH, RFC] Don't do page stablization if !CONFIG_BLKDEV_INTEGRITY Date: Thu, 8 Mar 2012 15:37:41 -0500 Message-ID: <20120308203741.GE29510@shiny> References: <4F57F523.3020703@redhat.com> <4F581BF6.8000305@zabbo.net> <20120308155419.GB6777@thunk.org> <20120308180951.GB29510@shiny> <4F59148A.4070001@panasas.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Ted Ts'o" , Zach Brown , Eric Sandeen , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org To: Boaz Harrosh Return-path: Received: from acsinet15.oracle.com ([141.146.126.227]:50603 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782Ab2CHUhv (ORCPT ); Thu, 8 Mar 2012 15:37:51 -0500 Content-Disposition: inline In-Reply-To: <4F59148A.4070001@panasas.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Mar 08, 2012 at 12:20:26PM -0800, Boaz Harrosh wrote: > On 03/08/2012 10:09 AM, Chris Mason wrote: > > > > But, why are we writeback for a second or more? Aren't there other > > parts of this we would want to fix as well? > > > > I'm not against only turning on stable pages when they are needed, but > > the code that isn't the default tends to be somewhat less used. So it > > does increase testing burden when we do want stable pages, and it tends > > to make for awkward bugs that are hard to reproduce because someone > > neglects to mention it. > > > > IMHO it's much more important to nail down the 2 second writeback > > latency. That's not good. > > > > I think I understand this one. It's do to the sync nature introduced > by page_waiting in mkwrite. Pages go from dirty to writeback for a few reasons. Background writeout, or O_DIRECT or someone running sync background writeout shouldn't be queueing up so much work that synchronous writeout has a 2 second delay. If the latencies are coming from something that was run through fsync...well there's not too much we can do about that. The problem is that our page_mkwrite call isn't starting the IO it is just waiting on it, so we can't bump the priority on it. -chris