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[195.135.220.15]) by mx.google.com with ESMTPS id g15si2489786ejd.9.2019.01.31.07.45.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Jan 2019 07:45:17 -0800 (PST) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz 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 E8B16B0B9; Thu, 31 Jan 2019 15:45:16 +0000 (UTC) Subject: Re: [PATCH 21/22] mm, compaction: Be selective about what pageblocks to clear skip hints To: Mel Gorman , Andrew Morton Cc: David Rientjes , Andrea Arcangeli , Linux List Kernel Mailing , Linux-MM References: <20190118175136.31341-1-mgorman@techsingularity.net> <20190118175136.31341-22-mgorman@techsingularity.net> From: Vlastimil Babka Openpgp: preference=signencrypt Message-ID: <9318efb7-cf20-b87d-9038-27406925b161@suse.cz> Date: Thu, 31 Jan 2019 16:45:16 +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: <20190118175136.31341-22-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 1/18/19 6:51 PM, Mel Gorman wrote: > Pageblock hints are cleared when compaction restarts or kswapd makes enough > progress that it can sleep but it's over-eager in that the bit is cleared > for migration sources with no LRU pages and migration targets with no free > pages. As pageblock skip hint flushes are relatively rare and out-of-band > with respect to kswapd, this patch makes a few more expensive checks to > see if it's appropriate to even clear the bit. Every pageblock that is > not cleared will avoid 512 pages being scanned unnecessarily on x86-64. > > The impact is variable with different workloads showing small differences > in latency, success rates and scan rates. This is expected as clearing > the hints is not that common but doing a small amount of work out-of-band > to avoid a large amount of work in-band later is generally a good thing. > > Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka