Re: [linus:master] [x86] 4817f70c25: stress-ng.mmapaddr.ops_per_sec 63.0% regression

[Matthew Wilcox]

On Wed, Jan 29, 2025 at 10:59:20AM -0500, Rik van Riel wrote:
> Below is a tentative fix for the issue. It is kind of a big hammer,
> and maybe the RCU people have a better idea on how to solve this
> problem, but it may be worth giving this a try to see if it helps
> with the regression you identified.

Perhaps better to do:

+++ b/mm/page_alloc.c
@@ -97,8 +97,8 @@ static DEFINE_MUTEX(pcp_batch_high_lock);
  * On SMP, spin_trylock is sufficient protection.
  * On PREEMPT_RT, spin_trylock is equivalent on both SMP and UP.
  */
-#define pcp_trylock_prepare(flags)     do { } while (0)
-#define pcp_trylock_finish(flag)       do { } while (0)
+#define pcp_trylock_prepare(flags)     rcu_read_lock()
+#define pcp_trylock_finish(flag)       rcu_reada_unlock()
 #else

 /* UP spin_trylock always succeeds so disable IRQs to prevent re-entrancy. */

with appropriate comment changes