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 S1751372AbaJQWEs (ORCPT <rfc822;w@1wt.eu>);
	Fri, 17 Oct 2014 18:04:48 -0400
Received: from mga03.intel.com ([134.134.136.65]:58621 "EHLO mga03.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750867AbaJQWEq (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 17 Oct 2014 18:04:46 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.04,741,1406617200"; 
   d="scan'208";a="591217535"
Message-ID: <54419265.9000000@intel.com>
Date: Fri, 17 Oct 2014 15:04:21 -0700
From: Dave Hansen <dave.hansen@intel.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.2
MIME-Version: 1.0
To: Dominik Dingel <dingel@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.cz>,
        Rik van Riel <riel@redhat.com>
CC: Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@amacapital.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Bob Liu <lliubbo@gmail.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Cornelia Huck <cornelia.huck@de.ibm.com>,
        Gleb Natapov <gleb@kernel.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@kernel.org>,
        Jianyu Zhan <nasa4836@gmail.com>, Johannes Weiner <hannes@cmpxchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Konstantin Weitz <konstantin.weitz@gmail.com>, kvm@vger.kernel.org,
        linux390@de.ibm.com, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sasha Levin <sasha.levin@oracle.com>
Subject: Re: [PATCH 2/4] mm: introduce new VM_NOZEROPAGE flag
References: <1413554990-48512-1-git-send-email-dingel@linux.vnet.ibm.com> <1413554990-48512-3-git-send-email-dingel@linux.vnet.ibm.com>
In-Reply-To: <1413554990-48512-3-git-send-email-dingel@linux.vnet.ibm.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 10/17/2014 07:09 AM, Dominik Dingel wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index cd33ae2..8f09c91 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -113,7 +113,7 @@ extern unsigned int kobjsize(const void *objp);
>  #define VM_GROWSDOWN	0x00000100	/* general info on the segment */
>  #define VM_PFNMAP	0x00000400	/* Page-ranges managed without "struct page", just pure PFN */
>  #define VM_DENYWRITE	0x00000800	/* ETXTBSY on write attempts.. */
> -
> +#define VM_NOZEROPAGE	0x00001000	/* forbid new zero page mappings */
>  #define VM_LOCKED	0x00002000
>  #define VM_IO           0x00004000	/* Memory mapped I/O or similar */

This seems like an awfully obscure use for a very constrained resource
(VM_ flags).

Is there ever a time where the VMAs under an mm have mixed VM_NOZEROPAGE
status?  Reading the patches, it _looks_ like it might be an all or
nothing thing.

Full disclosure: I've got an x86-specific feature I want to steal a flag
for.  Maybe we should just define another VM_ARCH bit.