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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 033FBC433F5 for ; Thu, 6 Sep 2018 14:12:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AF4982075B for ; Thu, 6 Sep 2018 14:12:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF4982075B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729478AbeIFSsY (ORCPT ); Thu, 6 Sep 2018 14:48:24 -0400 Received: from mga01.intel.com ([192.55.52.88]:11172 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728905AbeIFSsY (ORCPT ); Thu, 6 Sep 2018 14:48:24 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Sep 2018 07:12:40 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,338,1531810800"; d="scan'208";a="230726428" Received: from sgowrisa-mobl2.amr.corp.intel.com (HELO [10.251.16.54]) ([10.251.16.54]) by orsmga004.jf.intel.com with ESMTP; 06 Sep 2018 07:12:39 -0700 Subject: Re: [RFC][PATCH 2/5] [PATCH 2/5] proc: introduce /proc/PID/idle_bitmap To: Fengguang Wu , Andrew Morton References: <20180901112818.126790961@intel.com> <20180901124811.530300789@intel.com> Cc: Linux Memory Management List , Huang Ying , Brendan Gregg , Peng DongX , Liu Jingqi , Dong Eddie , kvm@vger.kernel.org, LKML From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180901124811.530300789@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/01/2018 04:28 AM, Fengguang Wu wrote: > To walk 1TB memory of 4k active pages, it costs 2s vs 15s system > time to scan the per-task/global idle bitmaps. To me, that says this interface simply won't work on large systems. 2s and 15s are both simply unacceptably long. > OTOH, the per-task idle bitmap is not suitable in some situations: > > - not accurate for shared pages > - don't work with non-mapped file pages > - don't perform well for sparse page tables (pointed out by Huang Ying) OK, so we have a new ABI that doesn't work on large systems, consumes lots of time and resources to query and isn't suitable in quite a few situations.