From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 12A5B8E0002 for ; Thu, 17 Jan 2019 12:17:31 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id x15so3977838edd.2 for ; Thu, 17 Jan 2019 09:17:31 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id i25si5462011edb.334.2019.01.17.09.17.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Jan 2019 09:17:29 -0800 (PST) Subject: Re: [PATCH 17/25] mm, compaction: Keep cached migration PFNs synced for unusable pageblocks 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 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: owner-linux-mm@kvack.org List-ID: To: Mel Gorman , Linux-MM Cc: David Rientjes , Andrea Arcangeli , ying.huang@intel.com, kirill@shutemov.name, Andrew Morton , Linux List Kernel Mailing 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 :)