From: Jeff Moyer Subject: Re: [PATCH, RFC] Don't do page stablization if !CONFIG_BLKDEV_INTEGRITY Date: Thu, 08 Mar 2012 15:42:52 -0500 Message-ID: References: <4F57F523.3020703@redhat.com> <4F581BF6.8000305@zabbo.net> <20120308155419.GB6777@thunk.org> <20120308180951.GB29510@shiny> <4F59148A.4070001@panasas.com> <20120308203741.GE29510@shiny> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Boaz Harrosh , "Ted Ts'o" , Zach Brown , Eric Sandeen , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org To: Chris Mason Return-path: Received: from mx1.redhat.com ([209.132.183.28]:62293 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751237Ab2CHUnA (ORCPT ); Thu, 8 Mar 2012 15:43:00 -0500 In-Reply-To: <20120308203741.GE29510@shiny> (Chris Mason's message of "Thu, 8 Mar 2012 15:37:41 -0500") Sender: linux-ext4-owner@vger.kernel.org List-ID: Chris Mason writes: > On Thu, Mar 08, 2012 at 12:20:26PM -0800, Boaz Harrosh wrote: >> 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. So now we're back to figuring out how to tell how long I/O will take? If writeback is issuing random access I/Os to spinning media, you can bet it might be a while. Today, you could lower nr_requests to some obscenely small number to improve worst-case latency. I thought there was some talk about improving the intelligence of writeback in this regard, but it's a tough problem, especially given that writeback isn't the only cook in the kitchen. Cheers, Jeff