Messages in this thread | | | Date | Tue, 24 Jul 2007 21:40:22 +0800 | From | "Shaohua Li" <> | Subject | Re: |
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> From: "Avi Kivity" <avi@qumranet.com> > To: "Li, Shaohua" <shaohua.li@intel.com> > Date: Tue, 24 Jul 2007 13:42:29 +0800 > Subject: Re: [RFC 0/8]KVM: swap out guest pages > > > Shaohua Li wrote: > > On Mon, 2007-07-23 at 18:27 +0800, Avi Kivity wrote: > > > >> Shaohua Li wrote: > >> > >>> This patch series make kvm guest pages be able to be swapped out and > >>> dynamically allocated. Without it, all guest memory is allocated at > >>> guest start time. > >>> > >>> patches are against latest git, and you need first patch Avi's > >>> > >> kvm-sch > >> > >>> integration patch > >>> > >>> > >> > (http://sourceforge.net/mailarchive/forum.php?thread_name=11841693332609-git-send-email-avi%40qumranet.com&forum_name=kvm-devel > ). > >> > >>> Patch is quite stable in my test. With the patch, I can run a 256M > >>> memory guest in a 300M memory host. > >>> > >> What about the opposite? > >> > >> > >>> If guest is idle, the memory it used > >>> can be less than 10M. I did a simple performance test (measure > >>> > >> kernel > >> > >>> build time in guest), if there is few swap, the performance w/wo the > >>> patch difference isn't significent. If you have better measurement > >>> approach, please let me try. > >>> > >>> Unresolved issue: > >>> 1. swapoff doesn't work, we need a hook. > >>> 2. SMP guest might not work, as kvm doesn't support smp till now. > >>> 3. better algorithm to select swaped out guest pages according to > >>> guest's memory usage. > >>> Maybe more. > >>> > >>> Any suggests and comments are appreciated. > >>> > >>> > >> The big question is whether to have kvm's own address_space or not. > >> > >> Having an address_space (like your patch does) is remarkably simple, > >> and > >> requires few hooks from the current vm. However using existing vmas > >> mapped by the user has many advantages: > >> > >> - compatible with s390 requirements > >> - allows the user to use hugetlbfs pages, which have a performance > >> advantage using ept/npt (but which are unswappable) > >> - allows the user to map a file (which can be regarded as way to > >> specify > >> the swap device) > >> - better ingration with the rest of the vm > >> > >> I am quite torn between the simplicity of your approach and the > >> advantages of using generic vmas. However, s390 pretty much forces > >> our > >> hand. > >> > >> What is your opinion of extending generic vmas to back kvm guest > >> memory? > >> > > several issues: > > 1. vma is to manage usersapce address, kvm guest uses full address > > space. > > 2. qemu itself must use some address space. > > > > My idea is to keep the current slot concept, but instead of having kvm > allocate pages for a slot, it would call get_user_pages() for a virtual > address range. Userspace doesn't directly talk about vmas, just virtual > address ranges. all the APIs need vma/page table handling. swap also needs vma for rmap for generic file.
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