From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751304AbdJDRjR (ORCPT <rfc822;w@1wt.eu>);
        Wed, 4 Oct 2017 13:39:17 -0400
Received: from userp1040.oracle.com ([156.151.31.81]:40986 "EHLO
        userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1750779AbdJDRjP (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 4 Oct 2017 13:39:15 -0400
Subject: Re: [RFC] mmap(MAP_CONTIG)
To: Christopher Lameter <cl@linux.com>,
        Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, Marek Szyprowski <m.szyprowski@samsung.com>,
        Michal Nazarewicz <mina86@mina86.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, Guy Shattah <sguy@mellanox.com>
References: <21f1ec96-2822-1189-1c95-79a2bb491571@oracle.com>
 <97c81533-5206-b130-1aeb-c5b9bfd93287@linux.vnet.ibm.com>
 <alpine.DEB.2.20.1710041104310.21484@nuc-kabylake>
From: Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <434a5870-0115-b8ab-bd6c-b7f4db847dc4@oracle.com>
Date: Wed, 4 Oct 2017 10:38:57 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.3.0
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.20.1710041104310.21484@nuc-kabylake>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-Source-IP: userv0021.oracle.com [156.151.31.71]
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 10/04/2017 09:05 AM, Christopher Lameter wrote:
> On Wed, 4 Oct 2017, Anshuman Khandual wrote:
> 
>>> - Using 'pre-allocated' pages in the fault paths may be intrusive.
>>
>> But we have already faulted in all of them for the mapping and they
>> are also locked. Hence there should not be any page faults any more
>> for the VMA. Am I missing something here ?
> 
> The PTEs may be torn down and have to reestablished through a page faults.
> Page faults would not allocate memory.
> 
>> I am still wondering why wait till fault time not pre fault all of them
>> and populate the page tables.
> 
> They are populated but some processes (swap and migration) may tear them
> down.

As mentioned in my reply to Anshuman, the mention of fault paths here
may be a source of confusion.  I would expect the entire mapping to be
populated at mmap time, and the pages locked.  Therefore, there should
be no swap or migration.

-- 
Mike Kravetz