From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753730AbcBXAje (ORCPT ); Tue, 23 Feb 2016 19:39:34 -0500 Received: from mail-pa0-f42.google.com ([209.85.220.42]:35184 "EHLO mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751611AbcBXAjd (ORCPT ); Tue, 23 Feb 2016 19:39:33 -0500 Date: Tue, 23 Feb 2016 16:39:31 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com 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 In-Reply-To: <1456184002-15729-1-git-send-email-hannes@cmpxchg.org> Message-ID: References: <1456184002-15729-1-git-send-email-hannes@cmpxchg.org> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 22 Feb 2016, 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. > > 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 Acked-by: David Rientjes