On 12 March 2014 16:30, Peter Zijlstra [off-list ref] wrote:

On Wed, Mar 12, 2014 at 04:20:15PM +0000, Steve Capper wrote:

quoted

On 12 March 2014 14:18, Peter Zijlstra [off-list ref] wrote:

quoted

Since you just went through the trouble of enabling RCU pagetable
freeing, you might also replace these local_irq_save/restore with
rcu_read_{,un}lock().

Hi Peter,
This critical section also needs to block the THP splitting code. At
the moment an IPI is broadcast in pmdp_splitting_flush. I'm not sure
how to adapt that to block on an rcu_read_lock, I'll have a think.

Ah, I've not looked at THP much at all.

Would it be sufficient to make sure to fail the pmd get_page()
equivalent early enough?

I don't think that will be enough, as we haven't locked anything. I'll
refine the IPI as per your suggestion.