From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 42DC5C43444 for ; Thu, 17 Jan 2019 17:17:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 12EC220856 for ; Thu, 17 Jan 2019 17:17:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728021AbfAQRRa (ORCPT ); Thu, 17 Jan 2019 12:17:30 -0500 Received: from mx2.suse.de ([195.135.220.15]:60092 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726223AbfAQRRa (ORCPT ); Thu, 17 Jan 2019 12:17:30 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id EF154ADE4; Thu, 17 Jan 2019 17:17:28 +0000 (UTC) Subject: Re: [PATCH 17/25] mm, compaction: Keep cached migration PFNs synced for unusable pageblocks To: Mel Gorman , Linux-MM Cc: David Rientjes , Andrea Arcangeli , ying.huang@intel.com, kirill@shutemov.name, Andrew Morton , Linux List Kernel Mailing References: <20190104125011.16071-1-mgorman@techsingularity.net> <20190104125011.16071-18-mgorman@techsingularity.net> From: Vlastimil Babka Message-ID: <2e384ff6-a4fd-5047-428d-b90cfa95be2e@suse.cz> Date: Thu, 17 Jan 2019 18:17:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190104125011.16071-18-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/4/19 1:50 PM, Mel Gorman wrote: > Migrate has separate cached PFNs for ASYNC and SYNC* migration on the > basis that some migrations will fail in ASYNC mode. However, if the cached > PFNs match at the start of scanning and pageblocks are skipped due to > having no isolation candidates, then the sync state does not matter. > This patch keeps matching cached PFNs in sync until a pageblock with > isolation candidates is found. > > The actual benefit is marginal given that the sync scanner following the > async scanner will often skip a number of pageblocks but it's useless > work. Any benefit depends heavily on whether the scanners restarted > recently so overall the reduction in scan rates is a mere 2.8% which > is borderline noise. > > Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka My easlier suggestion to check more thoroughly if pages can be migrated (which depends on the mode) before isolating them wouldn't play nice with this :)