Messages in this thread | | | Date | Tue, 13 Mar 2012 12:12:33 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH 2/4] KVM: Avoid checking huge page mappings in get_dirty_log() |
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On 03/13/2012 11:20 AM, Takuya Yoshikawa wrote: > Avi Kivity <avi@redhat.com> wrote: > > > It occurs to me that we should write-protect huge page tables, since it > > makes write protection much faster (we make up for this later at write > > fault time, but that might not occur, and even if it does we reduce > > guest jitter). In fact I once proposed a more involved variant, called > > Do you mean protecting huge page tables when we start logging and dropping > them, one by one, at the time of write fault?
Yes. Even more generally, protecting PML4Es, then at fault time un-protecting the faulting PML4E and write-protecting all underlying PDPEs except the one for the faulting address, and similarly for PDEs and PTEs.
> If so, we do not need to change get_dirty_log() implementation. > Changing kvm_mmu_remove_write_access() and fault handler seems to be enough. > > > O(1) write protection, in which we write-protect the topmost page table > > only and only un-write-protect the paths that fault. > > > That can be done later however and shouldn't affect this patchset. > > I have some additional patches to optimize rmap handling which seems to > improve get_dirty_log() about 10% in the worst case.
Great, looking forward.
> After that, I want to take some time to prepare for further developments > because my current test tools are not enough now. >
-- error compiling committee.c: too many arguments to function
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