[RFC PATCH V3 3/6] arm: mm: implement get_user_pages_fast

[Peter Zijlstra]

On Wed, Mar 12, 2014 at 04:20:15PM +0000, Steve Capper wrote:
> On 12 March 2014 14:18, Peter Zijlstra <peterz at infradead.org> wrote:
> > 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?