Messages in this thread | | | Date | Thu, 1 Apr 2010 09:15:51 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks() |
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On Thu, Apr 01, 2010 at 07:06:36PM +0300, Avi Kivity wrote: > On 04/01/2010 06:56 PM, Peter Zijlstra wrote: > >On Thu, 2010-04-01 at 18:51 +0300, Avi Kivity wrote: > >>On 04/01/2010 06:42 PM, Andrea Arcangeli wrote: > >>>On Thu, Apr 01, 2010 at 01:43:14PM +0200, Peter Zijlstra wrote: > >>> > >>>>On Thu, 2010-04-01 at 13:27 +0200, Peter Zijlstra wrote: > >>>> > >>>>>I've almost got a patch done that converts those two, still need to look > >>>>>where that tasklist_lock muck happens. > >>>>> > >>>>OK, so the below builds and boots, only need to track down that > >>>>tasklist_lock nesting, but I got to run an errand first. > >>>> > >>>You should have a look at my old patchset where Christoph already > >>>implemented this (and not for decreasing latency but to allow > >>>scheduling in mmu notifier handlers, only needed by XPMEM): > >>> > >>>http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.26-rc7/mmu-notifier-v18/ > >>> > >>>The ugliest part of it (that I think you missed below) is the breakage > >>>of the RCU locking in the anon-vma which requires adding refcounting > >>>to it. That was the worst part of the conversion as far as I can tell. > >>> > >>>http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.26-rc7/mmu-notifier-v18/anon-vma > >>> > >>Can we use srcu now instead? > >I would much rather we make call_rcu_preempt() available at all times. > > I don't understand. I thought the problem was that the locks were > taken inside an rcu critical section; switching to srcu would fix > that. But how is call_rcu_preempt() related? Grepping a bit, what > is call_rcu_preempt()? my tree doesn't have it.
I believe that Peter is referring to the RCU implementation you get with CONFIG_TREE_PREEMPT_RCU, which currently depends on CONFIG_PREEMPT. The other implementation is CONFIG_TREE_RCU, which is usually called "classic RCU".
Thanx, Paul
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