Re: [RFC] KVM guest page swap out support - take2

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Shaohua Li wrote:
> Hi,
> This is a updated patch set of swap out kvm guest pages.Changes are:
> 1. refresh against to kvm-26
> 2. clean up shadow page handling to make gfn_to_page not be called
> within kmap_atomic/kunamp_atomic.
> 3. variant bug fixing. Now the patch is quite stable in my test.
> 4. make swap out optional. A compile option can completely close swap
> out. There should be no performance impact if swapout isn't enabled.
>
> There are still a lot of unresolved issues:
> 1. just work for one vm. waiting for kvm hook into scheduler
> 2. Not work for mp guest and can't swap out pages which shadow page
> table point to, this require kvm .flush_tlb can send ipi to vcpu.
> 3. swapoff isn't supported. We need a hook to sys_swapoff for kvm.
>
> Please review, suggests and comments are welcome.
>
>   

The patch rmaps read-only guest pages.  While this is of course 
required, it will make unshadowing ptes pointing to shared library pages 
very expensive.  If we have a guest with 200 processes, all mapping 
glibc, then an exit() will have to walk a linear list of size 200 per 
shadowed pte.

Do you know how the Linux rmap implementation handles this?

An idea that comes to mind is to allocate an extra mm_struct for the 
guest and use the normal Linux vma management there.  I don't know how 
practical this is.

-- 
error compiling committee.c: too many arguments to function


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