On Mon, Mar 27, 2017 at 05:15:00PM +0200, Jesper Dangaard Brouer wrote:

And I also verified it worked:

  0.63 │       mov    __preempt_count,%eax
       │     free_hot_cold_page():
  1.25 │       test   $0x1f0000,%eax
       │     ↓ jne    1e4

And this simplification also made the compiler change this into a
unlikely branch, which is a micro-optimization (that I will leave up to
the compiler).

Excellent!  That said, I think we should define in_irq_or_nmi() in
preempt.h, rather than hiding it in the memory allocator.  And since we're
doing that, we might as well make it look like the other definitions:

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 7eeceac52dea..af98c29abd9d 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h

@@ -81,6 +81,7 @@
 #define in_interrupt()		(irq_count())
 #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
 #define in_nmi()		(preempt_count() & NMI_MASK)
+#define in_irq_or_nmi()		(preempt_count() & (HARDIRQ_MASK | NMI_MASK))
 #define in_task()		(!(preempt_count() & \
 				   (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
 

I think there are some genuine questions to be asked about the other
users of in_irq() whether they really want to use in_irq_or_nmi().
There's fewer than a hundred of them, so somebody sufficiently motivated
could take a look in a few days.

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