Re: [PATCH 0/2] Simplify RCU freeing of shadow pages

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Apr 19, 2012 at 07:26:35PM +0300, Avi Kivity wrote:
> This patchset simplifies the freeing by RCU of mmu pages.
> 
> Xiao, I'm sure you thought of always freeing by RCU.  Why didn't you choose
> this way?  I saves a couple of atomics in the fast path.
> 
> Avi Kivity (2):
>   KVM: MMU: Always free shadow pages using RCU
>   KVM: MMU: Recover space used by rcu_head in struct kvm_mmu_page
> 
>  arch/x86/include/asm/kvm_host.h |    9 +++---
>  arch/x86/kvm/mmu.c              |   58 ++++++++-------------------------------
>  2 files changed, 15 insertions(+), 52 deletions(-)

Check Documentation/RCU/checklist.txt item 8.

        a.      Keeping a count of the number of data-structure elements
                used by the RCU-protected data structure, including
                those waiting for a grace period to elapse.  Enforce a
                limit on this number, stalling updates as needed to allow
                previously deferred frees to complete.  Alternatively,
                limit only the number awaiting deferred free rather than
                the total number of elements.