Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758942Ab0LNNhr (ORCPT ); Tue, 14 Dec 2010 08:37:47 -0500 Received: from anchor-post-3.mail.demon.net ([195.173.77.134]:59931 "EHLO anchor-post-3.mail.demon.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751014Ab0LNNhq (ORCPT ); Tue, 14 Dec 2010 08:37:46 -0500 Subject: Re: [PATCH 04/35] writeback: reduce per-bdi dirty threshold ramp up time From: Richard Kennedy To: Wu Fengguang Cc: Andrew Morton , Jan Kara , Peter Zijlstra , Christoph Hellwig , Trond Myklebust , Dave Chinner , "Theodore Ts'o" , Chris Mason , Mel Gorman , Rik van Riel , KOSAKI Motohiro , Greg Thelen , Minchan Kim , linux-mm , linux-fsdevel@vger.kernel.org, LKML In-Reply-To: <20101213150326.856922289@intel.com> References: <20101213144646.341970461@intel.com> <20101213150326.856922289@intel.com> Content-Type: multipart/mixed; boundary="=-kuCK84pMs8//cNx5PF32" Date: Tue, 14 Dec 2010 13:37:34 +0000 Message-ID: <1292333854.2019.16.camel@castor.rsk> Mime-Version: 1.0 X-Mailer: Evolution 2.32.1 (2.32.1-1.fc14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7997 Lines: 160 --=-kuCK84pMs8//cNx5PF32 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit On Mon, 2010-12-13 at 22:46 +0800, Wu Fengguang wrote: > plain text document attachment > (writeback-speedup-per-bdi-threshold-ramp-up.patch) > Reduce the dampening for the control system, yielding faster > convergence. > > Currently it converges at a snail's pace for slow devices (in order of > minutes). For really fast storage, the convergence speed should be fine. > > It makes sense to make it reasonably fast for typical desktops. > > After patch, it converges in ~10 seconds for 60MB/s writes and 4GB mem. > So expect ~1s for a fast 600MB/s storage under 4GB mem, or ~4s under > 16GB mem, which seems reasonable. > > $ while true; do grep BdiDirtyThresh /debug/bdi/8:0/stats; sleep 1; done > BdiDirtyThresh: 0 kB > BdiDirtyThresh: 118748 kB > BdiDirtyThresh: 214280 kB > BdiDirtyThresh: 303868 kB > BdiDirtyThresh: 376528 kB > BdiDirtyThresh: 411180 kB > BdiDirtyThresh: 448636 kB > BdiDirtyThresh: 472260 kB > BdiDirtyThresh: 490924 kB > BdiDirtyThresh: 499596 kB > BdiDirtyThresh: 507068 kB > ... > DirtyThresh: 530392 kB > > CC: Peter Zijlstra > CC: Richard Kennedy > Signed-off-by: Wu Fengguang > --- > mm/page-writeback.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- linux-next.orig/mm/page-writeback.c 2010-12-13 21:46:11.000000000 +0800 > +++ linux-next/mm/page-writeback.c 2010-12-13 21:46:11.000000000 +0800 > @@ -145,7 +145,7 @@ static int calc_period_shift(void) > else > dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / > 100; > - return 2 + ilog2(dirty_total - 1); > + return ilog2(dirty_total - 1) - 1; > } > > /* > > Hi Fengguang, I've been running my test set on your v3 series and generally it's giving good results in line with the mainline kernel, with much less variability and lower standard deviation of the results so it is much more repeatable. However, it doesn't seem to be honouring the background_dirty_threshold. The attached graph is from a simple fio write test of 400Mb on ext4. All dirty pages are completely written in 15 seconds, but I expect to see up to background_dirty_threshold pages staying dirty until the 30 second background task writes them out. So it is much too eager to write back dirty pages. As to the ramp up time, when writing to 2 disks at the same time I see the per_bdi_threshold taking up to 20 seconds to converge on a steady value after one of the write stops. So I think this could be speeded up even more, at least on my setup. I am just about to start testing v4 & will report anything interesting. regards Richard --=-kuCK84pMs8//cNx5PF32 Content-Type: image/png; name="dirty.png" Content-Disposition: attachment; filename="dirty.png" Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSUhEUgAAAlgAAAGQBAMAAAH3HDM9AAAAD1BMVEX///8AAH9/f3//AAAA/wBh 082hAAANaElEQVR4nO2dC7KrrBKFpZIBaP13IPlr3wFwqzL/Md2g+AAb6E4QQdc6Z+eB2C4/efmK XfellOqGrv92bqPXEoqXNZ2NGa3SbI8zFpovm+qHtPwCk17oI4e3vNlUz8pmtJTxLNmYC0W2X7I9 YtnGTa8lC33qoqvwtH85CvncIL3i0dZ2K5VNM7Kt0tm46VS2l4XGirbLxpxFGPWGeqSz5JWU9yud RZAtm1jL+6J3hlYVL5vVK1XqmMROBPvs3qks2nn7eXlZJQvHya25wdItDiuUzVSoCJzQu/bLSw4p swaDt/9BLrbnNPccEcE32/7nNcsZa6NvY1EF8URffR+ZoQZey+bbgKvBV6WxyHauAl8brRWyrlir rhLL9kZkT/qlr02staj9vo45Y62qLNbCThqr9jY6Xyx6mHaVWNTocC4UGdg/db5Yi3LEethdg29j UfsVv/vSy2sWXnZDfheL3tn5NpaeP27AZVnHR8ZYXTWxVkp6/XD2garQ8gPppx/WHQ1M5vrPFxXr sy6gPgtyZfa3Va+UKrn9hq5XWffdhZuaXNfee68xluAgUtFYArUfK31csGisJcT3sZR5cWKlFYpl 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