From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49436) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XbSIU-0003pD-IP for qemu-devel@nongnu.org; Tue, 07 Oct 2014 06:47:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XbSIP-0003wx-Bm for qemu-devel@nongnu.org; Tue, 07 Oct 2014 06:47:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27196) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XbSIP-0003uv-51 for qemu-devel@nongnu.org; Tue, 07 Oct 2014 06:47:09 -0400 Date: Tue, 7 Oct 2014 11:46:04 +0100 From: "Dr. David Alan Gilbert" 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> Subject: Re: [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Kirill A. Shutemov" Cc: Robert Love , Dave Hansen , Jan Kara , kvm@vger.kernel.org, Neil Brown , Stefan Hajnoczi , qemu-devel@nongnu.org, linux-mm@kvack.org, KOSAKI Motohiro , Michel Lespinasse , Andrea Arcangeli , Taras Glek , Andrew Jones , Juan Quintela , Hugh Dickins , Isaku Yamahata , Mel Gorman , Sasha Levin , Android Kernel Team , "\\\"Dr. David Alan Gilbert\\\"" , "Huangpeng (Peter)" , Andres Lagar-Cavilla , Christopher Covington , Anthony Liguori , Mike Hommey , Keith Packard , Wenchao Xia , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Minchan Kim , Dmitry Adamushko , Johannes Weiner , Paolo Bonzini , Andrew Morton , Linus Torvalds , Peter Feiner * 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