From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [patch 0/6] Guest page hinting version 7. Date: Fri, 27 Mar 2009 20:06:03 -0400 Message-ID: <49CD69EB.6000000@redhat.com> References: <20090327150905.819861420@de.ibm.com> <1238195024.8286.562.camel@nimitz> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1238195024.8286.562.camel@nimitz> Sender: owner-linux-mm@kvack.org To: Dave Hansen Cc: Martin Schwidefsky , 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 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. > I don't see any description of it in there any more, but I thought this > entire patch set was to get rid of the idiotic triple I/Os in the > following scenario: > I don't see that mentioned at all in the current description. > Simplifying the hypervisor is hard to get behind, but cutting system I/O > by 2/3 is a much nicer benefit for 1200 lines of invasive code. ;) Cutting down on a fair bit of IO is absolutely worth 1200 lines of fairly well isolated code. > Can we persuade the hypervisor to tell us which pages it decided to page > out and just skip those when we're scanning the LRU? The easiest "notification" points are in the page fault handler and the page cache lookup code. -- All rights reversed. -- 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