From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f180.google.com (mail-lb0-f180.google.com [209.85.217.180]) by kanga.kvack.org (Postfix) with ESMTP id 4B49A6B0038 for ; Tue, 7 Oct 2014 06:53:32 -0400 (EDT) Received: by mail-lb0-f180.google.com with SMTP id f15so5785637lbj.25 for ; Tue, 07 Oct 2014 03:53:31 -0700 (PDT) Received: from kirsi1.inet.fi (mta-out1.inet.fi. [62.71.2.226]) by mx.google.com with ESMTP id p5si28049359laf.101.2014.10.07.03.53.30 for ; Tue, 07 Oct 2014 03:53:30 -0700 (PDT) Date: Tue, 7 Oct 2014 13:52:45 +0300 From: "Kirill A. Shutemov" Subject: Re: [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT Message-ID: <20141007105245.GC30762@node.dhcp.inet.fi> 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> <20141007104603.GI2404@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141007104603.GI2404@work-vm> Sender: owner-linux-mm@kvack.org List-ID: To: "Dr. David Alan Gilbert" 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 , "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 Tue, Oct 07, 2014 at 11:46:04AM +0100, Dr. David Alan Gilbert wrote: > * 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 ? No. If kernel would ignore MADV_DONTNEED or MADV_DONTDUMP it will not affect correctness, just behaviour will be suboptimal: more than needed memory used or wasted space in coredump. -- 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