Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753044AbaJFRZN (ORCPT ); Mon, 6 Oct 2014 13:25:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55482 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752578AbaJFRZK (ORCPT ); Mon, 6 Oct 2014 13:25:10 -0400 Date: Mon, 6 Oct 2014 19:24:15 +0200 From: Andrea Arcangeli To: Mike Hommey 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 , 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: <20141006172415.GC31075@redhat.com> References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-9-git-send-email-aarcange@redhat.com> <20141003231336.GA13528@glandium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141003231336.GA13528@glandium.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Sat, Oct 04, 2014 at 08:13:36AM +0900, Mike Hommey 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. > > What does "unmapped virtual address" mean in this context? To clarify this I added this in a second sentence in the commit header: "still unmapped virtual address" of the previous sentence in this context means that the pte/trans_huge_pmd is null. It means it's an hole inside the anonymous vma (the kind of hole that doesn't account for RSS but only virtual size of the process). It is the same state all anonymous virtual memory is, right after mmap. The same state that if you read from it, will map a zeropage into the faulting virtual address. If the page is swapped out, it will not trigger userfaults. If something isn't clear let me know. Thanks, Andrea -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/