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 S1753481AbaJGKrV (ORCPT <rfc822;w@1wt.eu>);
	Tue, 7 Oct 2014 06:47:21 -0400
Received: from mx1.redhat.com ([209.132.183.28]:22739 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752825AbaJGKrS (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Tue, 7 Oct 2014 06:47:18 -0400
Date: Tue, 7 Oct 2014 11:46:04 +0100
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andrea Arcangeli <aarcange@redhat.com>, qemu-devel@nongnu.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-api@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andres Lagar-Cavilla <andreslc@google.com>,
        Dave Hansen <dave@sr71.net>, Paolo Bonzini <pbonzini@redhat.com>,
        Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>,
        Andy Lutomirski <luto@amacapital.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sasha Levin <sasha.levin@oracle.com>, Hugh Dickins <hughd@google.com>,
        Peter Feiner <pfeiner@google.com>,
        "\\\"Dr. David Alan Gilbert\\\"" <dgilbert@redhat.com>,
        Christopher Covington <cov@codeaurora.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Android Kernel Team <kernel-team@android.com>,
        Robert Love <rlove@google.com>,
        Dmitry Adamushko <dmitry.adamushko@gmail.com>,
        Neil Brown <neilb@suse.de>, Mike Hommey <mh@glandium.org>,
        Taras Glek <tglek@mozilla.com>, Jan Kara <jack@suse.cz>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Michel Lespinasse <walken@google.com>,
        Minchan Kim <minchan@kernel.org>, Keith Packard <keithp@keithp.com>,
        "Huangpeng (Peter)" <peter.huangpeng@huawei.com>,
        Isaku Yamahata <yamahata@valinux.co.jp>,
        Anthony Liguori <anthony@codemonkey.ws>,
        Stefan Hajnoczi <stefanha@gmail.com>,
        Wenchao Xia <wenchaoqemu@gmail.com>, Andrew Jones <drjones@redhat.com>,
        Juan Quintela <quintela@redhat.com>
Subject: Re: [PATCH 08/17] mm: madvise MADV_USERFAULT
Message-ID: <20141007104603.GI2404@work-vm>
References: <1412356087-16115-1-git-send-email-aarcange@redhat.com>
 <1412356087-16115-9-git-send-email-aarcange@redhat.com>
 <20141007103645.GB30762@node.dhcp.inet.fi>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20141007103645.GB30762@node.dhcp.inet.fi>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

* Kirill A. Shutemov (kirill@shutemov.name) wrote:
> On Fri, Oct 03, 2014 at 07:07:58PM +0200, Andrea Arcangeli wrote:
> > MADV_USERFAULT is a new madvise flag that will set VM_USERFAULT in the
> > vma flags. Whenever VM_USERFAULT is set in an anonymous vma, if
> > userland touches a still unmapped virtual address, a sigbus signal is
> > sent instead of allocating a new page. The sigbus signal handler will
> > then resolve the page fault in userland by calling the
> > remap_anon_pages syscall.
> 
> Hm. I wounder if this functionality really fits madvise(2) interface: as
> far as I understand it, it provides a way to give a *hint* to kernel which
> may or may not trigger an action from kernel side. I don't think an
> application will behaive reasonably if kernel ignore the *advise* and will
> not send SIGBUS, but allocate memory.

Aren't DONTNEED and DONTDUMP  similar cases of madvise operations that are
expected to do what they say ?

> I would suggest to consider to use some other interface for the
> functionality: a new syscall or, perhaps, mprotect().

Dave

> -- 
>  Kirill A. Shutemov
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK