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    SubjectRe: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb_others
    On 05/01/2012 06:14 PM, Peter Zijlstra wrote:
    > On Tue, 2012-05-01 at 15:12 +0300, Avi Kivity wrote:
    > >
    > > What's changed is not gup_fast() but the performance of munmap(),
    > > exit(), and exec(), no?
    >
    > If it is indeed cache related like you suggested earlier, it would be
    > the allocation side of things, like fork()/mmap() that suffer since
    > there's fewer hot pages about, but yes, anything creating/destroying
    > page-tables.

    Right.

    >
    > > What bounds the amount of memory waiting to be freed during an rcu grace
    > > period?
    >
    > Most RCU implementations don't have limits, so that could be quite a
    > lot. I think preemptible RCU has a batch limit at which point it tries
    > rather hard to force a grace period, but I'm not sure if even that
    > provides a hard limit.
    >
    > Practically though, I haven't had reports of PPC/Sparc going funny
    > because of this.

    It could be considered a DoS if a user is able to free page tables
    faster than rcu is able to recycle them, possibly triggering the oom
    killer (should that force a grace period before firing from the hip?)

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



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