might_fault is called from functions like copy_to_user
which most callers expect to be very fast, like
a couple of instructions. So functions like memcpy_toiovec call them
many times in a loop.
But might_fault calls might_sleep() and with CONFIG_PREEMPT_VOLUNTARY
this results in a function call.
Let's not do this - just call __might_sleep that produces
a diagnostic for sleep within atomic, but drop
might_preempt().
Here's a test sending traffic between the VM and the host,
host is built with CONFIG_PREEMPT_VOLUNTARY:
Before:
incoming: 7122.77 Mb/s
outgoing: 8480.37 Mb/s
after:
incoming: 8619.24 Mb/s
outgoing: 9455.42 Mb/s
As a side effect, this fixes an issue pointed
out by Ingo: might_fault might schedule differently
depending on PROVE_LOCKING. Now there's no
preemption point in both cases, so it's consistent.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
include/linux/kernel.h | 2 +-
mm/memory.c | 3 ++-
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e96329c..c514c06 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -198,7 +198,7 @@ void might_fault(void);
#else
static inline void might_fault(void)
{
- might_sleep();
+ __might_sleep(__FILE__, __LINE__, 0);
}
#endif
diff --git a/mm/memory.c b/mm/memory.c
index 6dc1882..c1f190f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4222,7 +4222,8 @@ void might_fault(void)
if (segment_eq(get_fs(), KERNEL_DS))
return;
- might_sleep();
+ __might_sleep(__FILE__, __LINE__, 0);
+
/*
* it would be nicer only to annotate paths which are not under
* pagefault_disable, however that requires a larger audit and
--
MST
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