Messages in this thread | | | Date | Fri, 27 Mar 2009 20:06:03 -0400 | From | Rik van Riel <> | Subject | Re: [patch 0/6] Guest page hinting version 7. |
| |
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.
| |