From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757044AbcBYAg2 (ORCPT ); Wed, 24 Feb 2016 19:36:28 -0500 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:46600 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751949AbcBYAg1 (ORCPT ); Wed, 24 Feb 2016 19:36:27 -0500 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Thu, 25 Feb 2016 09:37:44 +0900 From: Joonsoo Kim To: Johannes Weiner Cc: Andrew Morton , Mel Gorman , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v2] mm: scale kswapd watermarks in proportion to memory Message-ID: <20160225003744.GC9723@js1304-P5Q-DELUXE> References: <1456184002-15729-1-git-send-email-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1456184002-15729-1-git-send-email-hannes@cmpxchg.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Johannes. Just nitpick below. On Mon, Feb 22, 2016 at 03:33:22PM -0800, Johannes Weiner wrote: > In machines with 140G of memory and enterprise flash storage, we have > seen read and write bursts routinely exceed the kswapd watermarks and > cause thundering herds in direct reclaim. Unfortunately, the only way > to tune kswapd aggressiveness is through adjusting min_free_kbytes - > the system's emergency reserves - which is entirely unrelated to the > system's latency requirements. In order to get kswapd to maintain a > 250M buffer of free memory, the emergency reserves need to be set to > 1G. That is a lot of memory wasted for no good reason. > > On the other hand, it's reasonable to assume that allocation bursts > and overall allocation concurrency scale with memory capacity, so it > makes sense to make kswapd aggressiveness a function of that as well. > > Change the kswapd watermark scale factor from the currently fixed 25% > of the tunable emergency reserve to a tunable 0.001% of memory. s/0.001%/0.1% > Beyond 1G of memory, this will produce bigger watermark steps than the > current formula in default settings. Ensure that the new formula never > chooses steps smaller than that, i.e. 25% of the emergency reserve. > > On a 140G machine, this raises the default watermark steps - the > distance between min and low, and low and high - from 16M to 143M. > > Signed-off-by: Johannes Weiner > Acked-by: Mel Gorman > --- > Documentation/sysctl/vm.txt | 18 ++++++++++++++++++ > include/linux/mm.h | 1 + > include/linux/mmzone.h | 2 ++ > kernel/sysctl.c | 10 ++++++++++ > mm/page_alloc.c | 29 +++++++++++++++++++++++++++-- > 5 files changed, 58 insertions(+), 2 deletions(-) > > v2: Ensure 25% of emergency reserves as a minimum on small machines -Rik > > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt > index 89a887c..b02d940 100644 > --- a/Documentation/sysctl/vm.txt > +++ b/Documentation/sysctl/vm.txt > @@ -803,6 +803,24 @@ performance impact. Reclaim code needs to take various locks to find freeable > directory and inode objects. With vfs_cache_pressure=1000, it will look for > ten times more freeable objects than there are. > > +============================================================= > + > +watermark_scale_factor: > + > +This factor controls the aggressiveness of kswapd. It defines the > +amount of memory left in a node/system before kswapd is woken up and > +how much memory needs to be free before kswapd goes back to sleep. > + > +The unit is in fractions of 10,000. The default value of 10 means the > +distances between watermarks are 0.001% of the available memory in the > +node/system. The maximum value is 1000, or 10% of memory. Ditto for 0.001%. Thanks.