From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41249) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xb463-0002ht-P7 for qemu-devel@nongnu.org; Mon, 06 Oct 2014 04:56:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xb45w-0001j9-TB for qemu-devel@nongnu.org; Mon, 06 Oct 2014 04:56:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36241) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xb45w-0001ip-LI for qemu-devel@nongnu.org; Mon, 06 Oct 2014 04:56:40 -0400 Date: Mon, 6 Oct 2014 09:55:41 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20141006085540.GD2336@work-vm> References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-11-git-send-email-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH 10/17] mm: rmap preparation for remap_anon_pages List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Linus Torvalds Cc: Robert Love , Dave Hansen , Jan Kara , KVM list , Neil Brown , Stefan Hajnoczi , qemu-devel@nongnu.org, linux-mm , 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 , Linux Kernel Mailing List , Andy Lutomirski , Minchan Kim , Dmitry Adamushko , Johannes Weiner , Paolo Bonzini , Andrew Morton , Peter Feiner * Linus Torvalds (torvalds@linux-foundation.org) wrote: > On Fri, Oct 3, 2014 at 10:08 AM, Andrea Arcangeli wrote: > > > > Overall this looks a fairly small change to the rmap code, notably > > less intrusive than the nonlinear vmas created by remap_file_pages. > > Considering that remap_file_pages() was an unmitigated disaster, and > -mm has a patch to remove it entirely, I'm not at all convinced this > is a good argument. > > We thought remap_file_pages() was a good idea, and it really really > really wasn't. Almost nobody used it, why would the anonymous page > case be any different? I've posted code that uses this interface to qemu-devel and it works nicely; so chalk up at least one user. For the postcopy case I'm using it for, we need to place a page, atomically some thread might try and access it, and must either 1) get caught by userfault etc or 2) must succeed in it's access and we'll have that happening somewhere between thousands and millions of times to pages in no particular order, so we need to avoid creating millions of mappings. Dave > > Linus -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK