From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kirill A. Shutemov" Subject: Re: [PATCH 08/17] mm: madvise MADV_USERFAULT Date: Tue, 7 Oct 2014 13:36:45 +0300 Message-ID: <20141007103645.GB30762@node.dhcp.inet.fi> References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-9-git-send-email-aarcange@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1412356087-16115-9-git-send-email-aarcange@redhat.com> Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Linus Torvalds , Andres Lagar-Cavilla , Dave Hansen , Paolo Bonzini , Rik van Riel , Mel Gorman , Andy Lutomirski , Andrew Morton , Sasha Levin , Hugh Dickins , Peter Feiner , "\\\"Dr. David Alan Gilbert\\\"" , Christopher Covington , Johannes Weiner , Android Kernel Team , Robert Love , Dmitry Adamushko , Neil Brown , Mike Hommey , Taras Glek List-Id: linux-api@vger.kernel.org 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. I would suggest to consider to use some other interface for the functionality: a new syscall or, perhaps, mprotect(). -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kirill A. Shutemov" Subject: Re: [PATCH 08/17] mm: madvise MADV_USERFAULT Date: Tue, 7 Oct 2014 13:36:45 +0300 Message-ID: <20141007103645.GB30762@node.dhcp.inet.fi> References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-9-git-send-email-aarcange@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Linus Torvalds , Andres Lagar-Cavilla , Dave Hansen , Paolo Bonzini , Rik van Riel , Mel Gorman , Andy Lutomirski , Andrew Morton , Sasha Levin , Hugh Dickins , Peter Feiner , "\\\"Dr. David Alan Gilbert\\\"" , Christopher Covington , Johannes Weiner , Android Kernel Team , Robert Love , Dmitry Adamushko , Neil Brown , Mike Hommey , Taras Glek Return-path: Content-Disposition: inline In-Reply-To: <1412356087-16115-9-git-send-email-aarcange@redhat.com> Sender: owner-linux-mm@kvack.org List-Id: kvm.vger.kernel.org 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. I would suggest to consider to use some other interface for the functionality: a new syscall or, perhaps, mprotect(). -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f51.google.com (mail-wg0-f51.google.com [74.125.82.51]) by kanga.kvack.org (Postfix) with ESMTP id 594C16B0038 for ; Tue, 7 Oct 2014 06:37:42 -0400 (EDT) Received: by mail-wg0-f51.google.com with SMTP id b13so8781747wgh.34 for ; Tue, 07 Oct 2014 03:37:41 -0700 (PDT) Received: from jenni2.inet.fi (mta-out1.inet.fi. [62.71.2.226]) by mx.google.com with ESMTP id ws1si20476979wjb.85.2014.10.07.03.37.41 for ; Tue, 07 Oct 2014 03:37:41 -0700 (PDT) Date: Tue, 7 Oct 2014 13:36:45 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 08/17] mm: madvise MADV_USERFAULT Message-ID: <20141007103645.GB30762@node.dhcp.inet.fi> References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-9-git-send-email-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1412356087-16115-9-git-send-email-aarcange@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Linus Torvalds , Andres Lagar-Cavilla , Dave Hansen , Paolo Bonzini , Rik van Riel , Mel Gorman , Andy Lutomirski , Andrew Morton , Sasha Levin , Hugh Dickins , Peter Feiner , "\\\"Dr. David Alan Gilbert\\\"" , Christopher Covington , Johannes Weiner , Android Kernel Team , Robert Love , Dmitry Adamushko , Neil Brown , Mike Hommey , Taras Glek , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Minchan Kim , Keith Packard , "Huangpeng (Peter)" , Isaku Yamahata , Anthony Liguori , Stefan Hajnoczi , Wenchao Xia , Andrew Jones , Juan Quintela 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. I would suggest to consider to use some other interface for the functionality: a new syscall or, perhaps, mprotect(). -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753470AbaJGKiB (ORCPT ); Tue, 7 Oct 2014 06:38:01 -0400 Received: from mta-out1.inet.fi ([62.71.2.197]:40925 "EHLO jenni2.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752758AbaJGKh6 (ORCPT ); Tue, 7 Oct 2014 06:37:58 -0400 Date: Tue, 7 Oct 2014 13:36:45 +0300 From: "Kirill A. Shutemov" To: Andrea Arcangeli Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Linus Torvalds , Andres Lagar-Cavilla , Dave Hansen , Paolo Bonzini , Rik van Riel , Mel Gorman , Andy Lutomirski , Andrew Morton , Sasha Levin , Hugh Dickins , Peter Feiner , "\\\"Dr. David Alan Gilbert\\\"" , Christopher Covington , Johannes Weiner , Android Kernel Team , Robert Love , Dmitry Adamushko , Neil Brown , Mike Hommey , Taras Glek , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Minchan Kim , Keith Packard , "Huangpeng (Peter)" , Isaku Yamahata , Anthony Liguori , Stefan Hajnoczi , Wenchao Xia , Andrew Jones , Juan Quintela Subject: Re: [PATCH 08/17] mm: madvise MADV_USERFAULT Message-ID: <20141007103645.GB30762@node.dhcp.inet.fi> References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-9-git-send-email-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1412356087-16115-9-git-send-email-aarcange@redhat.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. I would suggest to consider to use some other interface for the functionality: a new syscall or, perhaps, mprotect(). -- Kirill A. Shutemov From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48223) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XbS9O-0000mg-Vv for qemu-devel@nongnu.org; Tue, 07 Oct 2014 06:37:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XbS9I-0001Jg-Vz for qemu-devel@nongnu.org; Tue, 07 Oct 2014 06:37:50 -0400 Received: from mta-out1.inet.fi ([62.71.2.226]:55252 helo=jenni2.inet.fi) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XbS9I-0001JW-Lv for qemu-devel@nongnu.org; Tue, 07 Oct 2014 06:37:44 -0400 Date: Tue, 7 Oct 2014 13:36:45 +0300 From: "Kirill A. Shutemov" Message-ID: <20141007103645.GB30762@node.dhcp.inet.fi> References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-9-git-send-email-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1412356087-16115-9-git-send-email-aarcange@redhat.com> Subject: Re: [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Arcangeli 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 , 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 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. I would suggest to consider to use some other interface for the functionality: a new syscall or, perhaps, mprotect(). -- Kirill A. Shutemov