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 73AE5C04AB8 for ; Fri, 14 Sep 2018 00:25:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3497220861 for ; Fri, 14 Sep 2018 00:25:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3497220861 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 S1728289AbeINFhW (ORCPT ); Fri, 14 Sep 2018 01:37:22 -0400 Received: from mga11.intel.com ([192.55.52.93]:20575 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726873AbeINFhW (ORCPT ); Fri, 14 Sep 2018 01:37:22 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Sep 2018 17:25:32 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,371,1531810800"; d="scan'208";a="257100162" Received: from dhhough-mobl.amr.corp.intel.com (HELO [10.251.3.163]) ([10.251.3.163]) by orsmga005.jf.intel.com with ESMTP; 13 Sep 2018 17:25:32 -0700 Subject: Re: [PATCH V2 0/6] VA to numa node information To: Andrew Morton , prakash.sangappa@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> <20180913171016.55dca2453c0773fc21044972@linux-foundation.org> Cc: Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, nao.horiguchi@gmail.com, kirill.shutemov@linux.intel.com, khandual@linux.vnet.ibm.com, steven.sistare@oracle.com 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: <20180913171016.55dca2453c0773fc21044972@linux-foundation.org> 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 09/13/2018 05:10 PM, Andrew Morton wrote: >> 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. As we are judging whether this is a "good" interface, can you tell us a bit about its scalability? For instance, let's say someone has a 1TB VMA that's populated with interleaved 4k pages. How much data comes out? How long does it take to parse? Will we effectively deadlock the system if someone accidentally cat's the wrong /proc file? /proc seems like a really simple way to implement this, but it seems a *really* odd choice for something that needs to collect a large amount of data. The lseek() stuff is a nice addition, but I wonder if it's unwieldy to use in practice. For instance, if you want to read data for the VMA at 0x1000000 you lseek(fd, 0x1000000, SEEK_SET, right? You read ~20 bytes of data and then the fd is at 0x1000020. But, you're getting data out at the next read() for (at least) the next page, which is also available at 0x1001000. Seems funky. Do other /proc files behave this way?