On 2011-02-10 15:47, Avi Kivity wrote: > On 02/10/2011 04:34 PM, Jan Kiszka wrote: >> On 2011-02-10 15:26, Avi Kivity wrote: >>> On 02/10/2011 03:47 PM, Jan Kiszka wrote: >>>>>> >>>>>> Accept for mmu_shrink, which is write but not delete, thus works without >>>>>> that slow synchronize_rcu. >>>>> >>>>> I don't really see how you can implement list_move_rcu(), it has to be >>>>> atomic or other users will see a partial vm_list. >>>> >>>> Right, even if we synchronized that step cleanly, rcu-protected users >>>> could miss the moving vm during concurrent list walks. >>>> >>>> What about using a separate mutex for protecting vm_list instead? >>>> Unless I missed some detail, mmu_shrink should allow blocking. >>> >>> What else does kvm_lock protect? >> >> Someone tried to write a locking.txt and stated that it's also >> protecting enabling/disabling hardware virtualization. But that guy may >> have overlooked something. > > Right. I guess splitting that lock makes sense. > >>> >>> I think we could simply reduce the amount of time we hold kvm_lock. >>> Pick a vm, ref it, list_move_tail(), unlock, then do the actual >>> shrinking. Of course taking a ref must be done carefully, we might >>> already be in kvm_destroy_vm() at that time. >>> >> >> Plain mutex held across the whole mmu_shrink loop is still simpler and >> should be sufficient - unless we also have to deal with scalability >> issues if that handler is able to run concurrently. But based on how we >> were using kvm_lock so far... > > I don't think a mutex would work for kvmclock_cpufreq_notifier(). At > the very least, we'd need a preempt_disable() there. At the worst, the > notifier won't like sleeping. Damn, there was that other user. Yes, this means we need to break the lock in mmu_shrink. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
