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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 4588FC433DF for ; Mon, 22 Jun 2020 21:07:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0BA5420732 for ; Mon, 22 Jun 2020 21:07:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0BA5420732 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 985196B0002; Mon, 22 Jun 2020 17:07:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9361D6B0005; 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Mon, 22 Jun 2020 21:07:55 +0000 (UTC) IronPort-SDR: unxHXXgCmRcIfcFxSYUVM5OmhzTjo+L/kgeBpNQ2RQAZ4ZdI3RT5RvQioVyZF6Ap+Gw76bqDW2 0ps33nnGXEZw== X-IronPort-AV: E=McAfee;i="6000,8403,9660"; a="142133742" X-IronPort-AV: E=Sophos;i="5.75,268,1589266800"; d="scan'208";a="142133742" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Jun 2020 14:07:53 -0700 IronPort-SDR: kLxBP3WAP8s0xA6vSs6ryvEMBxQBy9EUfg9f7GAUxmJGD9sMvfLQUswb3bOlD1C7kJYLfygw51 vM1xQNeGo5hA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,268,1589266800"; d="scan'208";a="278890877" Received: from gdeschee-mobl.amr.corp.intel.com (HELO [10.255.6.183]) ([10.255.6.183]) by orsmga006.jf.intel.com with ESMTP; 22 Jun 2020 14:07:49 -0700 Subject: Re: [PATCH 00/18] multiple preferred nodes To: Andi Kleen , Ben Widawsky Cc: linux-mm , Andrew Morton , Christoph Lameter , Dan Williams , Dave Hansen , David Hildenbrand , David Rientjes , Jason Gunthorpe , Johannes Weiner , Jonathan Corbet , Kuppuswamy Sathyanarayanan , Lee Schermerhorn , Li Xinhai , Mel Gorman , Michal Hocko , Mike Kravetz , Mina Almasry , Tejun Heo , Vlastimil Babka References: <20200619162425.1052382-1-ben.widawsky@intel.com> <20200622205430.GA818054@tassilo.jf.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200622205430.GA818054@tassilo.jf.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Rspamd-Queue-Id: E020D3856A X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 Content-Transfer-Encoding: quoted-printable 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 6/22/20 1:54 PM, Andi Kleen wrote: > On Fri, Jun 19, 2020 at 09:24:07AM -0700, Ben Widawsky wrote: >> This patch series introduces the concept of the MPOL_PREFERRED_MANY me= mpolicy. > So the reason for having a new policy is that you're worried some legac= y > application passes multiple nodes to MPOL_PREFERRED, where all but the > first would be currently ignored. Is that right? It's one thing if our internal implementation threw away all but the first preferred node silently. We do that, but we also go pretty far to blab in the manpage to solidify this behavior: If nodemask specifies more than one node ID, the first node in the mask will be selected as the preferred node. I think it's dangerous to go and actively break that promise. It means that newer apps will silently not get the behavior they ask for if they run on an old kernel. We also promise: The kernel will try to allocate pages from this node first and fall back to "near by" nodes if the preferred node is low on free memory. A user could legitimately say that the kernel breaks this promise if they passed multiple preferred nodes, one of them had lots of free memory, and that node node was not preferred.