Messages in this thread | | | Date | Tue, 01 May 2012 18:36:20 +0300 | From | Avi Kivity <> | Subject | Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb_others |
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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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