From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Schwidefsky Subject: Re: [patch 0/6] Guest page hinting version 7. Date: Sun, 29 Mar 2009 16:20:24 +0200 Message-ID: <20090329162024.687196ab@skybase> References: <20090327150905.819861420@de.ibm.com> <1238195024.8286.562.camel@nimitz> <49CD69EB.6000000@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49CD69EB.6000000@redhat.com> Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: Dave Hansen , linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.osdl.org, frankeh@watson.ibm.com, akpm@osdl.org, nickpiggin@yahoo.com.au, hugh@veritas.com List-Id: virtualization@lists.linuxfoundation.org On Fri, 27 Mar 2009 20:06:03 -0400 Rik van Riel wrote: > Dave Hansen wrote: > > On Fri, 2009-03-27 at 16:09 +0100, Martin Schwidefsky wrote: > >> If the host picks one of the > >> pages the guest can recreate, the host can throw it away instead of writing > >> it to the paging device. Simple and elegant. > > > > Heh, simple and elegant for the hypervisor. But I'm not sure I'm going > > to call *anything* that requires a new CPU instruction elegant. ;) > > I am convinced that it could be done with a guest-writable > "bitmap", with 2 bits per page. That would make this scheme > useful for KVM, too. This was our initial approach before we came up with the milli-code instruction. The reason we did not use a bitmap was to prevent the guest to change the host state (4 guest states U/S/V/P and 3 host states r/p/z). With the full set of states you'd need 4 bits. And the hosts need to have a "master" copy of the host bits, one the guest cannot change, otherwise you get into trouble. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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