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

[Steve Capper]

On 12 March 2014 16:30, Peter Zijlstra <peterz at infradead.org> wrote:
> 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?

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