From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751647AbeFEJ6q (ORCPT ); Tue, 5 Jun 2018 05:58:46 -0400 Received: from outbound-smtp25.blacknight.com ([81.17.249.193]:38065 "EHLO outbound-smtp25.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751473AbeFEJ6o (ORCPT ); Tue, 5 Jun 2018 05:58:44 -0400 Date: Tue, 5 Jun 2018 10:58:43 +0100 From: Mel Gorman To: Srikar Dronamraju Cc: Ingo Molnar , Peter Zijlstra , LKML , Rik van Riel , Thomas Gleixner Subject: Re: [PATCH 18/19] sched/numa: Reset scan rate whenever task moves across nodes Message-ID: <20180605095843.gfanebla26zvq62j@techsingularity.net> References: <1528106428-19992-1-git-send-email-srikar@linux.vnet.ibm.com> <1528106428-19992-19-git-send-email-srikar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1528106428-19992-19-git-send-email-srikar@linux.vnet.ibm.com> User-Agent: NeoMutt/20170912 (1.9.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 04, 2018 at 03:30:27PM +0530, Srikar Dronamraju wrote: > Currently task scan rate is reset when numa balancer migrates the task > to a different node. If numa balancer initiates a swap, reset is only > applicable to the task that initiates the swap. Similarly no scan rate > reset is done if the task is migrated across nodes by traditional load > balancer. > > Instead move the scan reset to the migrate_task_rq. This ensures the > task moved out of its preferred node, either gets back to its preferred > node quickly or finds a new preferred node. Doing so, would be fair to > all tasks migrating across nodes. > By and large you need to be very careful resetting the scan rate without a lot of justification and I don't think this is enough. With scan rate resets, there is a significant risk that system CPU overhead is increased to do the page table updates and handle the resulting minor faults. There are cases where tasks can get pulled cross-node very frequently and we do not want NUMA balancing scanning agressively when that happens. -- Mel Gorman SUSE Labs