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,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 1FEC5C04AB8 for ; Fri, 14 Sep 2018 00:10:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9D0F208E7 for ; Fri, 14 Sep 2018 00:10:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C9D0F208E7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org 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 S1728239AbeINFWG (ORCPT ); Fri, 14 Sep 2018 01:22:06 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:56782 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726921AbeINFWG (ORCPT ); Fri, 14 Sep 2018 01:22:06 -0400 Received: from localhost.localdomain (c-24-4-154-175.hsd1.ca.comcast.net [24.4.154.175]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 42083C5C; Fri, 14 Sep 2018 00:10:18 +0000 (UTC) Date: Thu, 13 Sep 2018 17:10:16 -0700 From: Andrew Morton To: prakash.sangappa@oracle.com Cc: Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, dave.hansen@intel.com, nao.horiguchi@gmail.com, kirill.shutemov@linux.intel.com, khandual@linux.vnet.ibm.com, steven.sistare@oracle.com Subject: Re: [PATCH V2 0/6] VA to numa node information Message-Id: <20180913171016.55dca2453c0773fc21044972@linux-foundation.org> In-Reply-To: <375951d0-f103-dec3-34d8-bbeb2f45f666@oracle.com> References: <1536783844-4145-1-git-send-email-prakash.sangappa@oracle.com> <20180913084011.GC20287@dhcp22.suse.cz> <375951d0-f103-dec3-34d8-bbeb2f45f666@oracle.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 13 Sep 2018 15:32:25 -0700 "prakash.sangappa" wrote: > >> https://marc.info/?t=152524073400001&r=1&w=2 > > It would be really great to give a short summary of the previous > > discussion. E.g. why do we need a proc interface in the first place when > > we already have an API to query for the information you are proposing to > > export [1] > > > > [1] http://lkml.kernel.org/r/20180503085741.GD4535@dhcp22.suse.cz > > The proc interface provides an efficient way to export address range > to numa node id mapping information compared to using the API. > For example, for sparsely populated mappings, if a VMA has large portions > not have any physical pages mapped, the page walk done thru the /proc file > interface can skip over non existent PMDs / ptes. Whereas using the > API the application would have to scan the entire VMA in page size units. > > Also, VMAs having THP pages can have a mix of 4k pages and hugepages. > The page walks would be efficient in scanning and determining if it is > a THP huge page and step over it. Whereas using the API, the application > would not know what page size mapping is used for a given VA and so would > have to again scan the VMA in units of 4k page size. > > If this sounds reasonable, I can add it to the commit / patch description. Preferably with some runtime measurements, please. How much faster is this interface in real-world situations? And why does that performance matter? It would also be useful to see more details on how this info helps operators understand/tune/etc their applications and workloads. In other words, I'm trying to get an understanding of how useful this code might be to our users in general.