mm: make lru_add_drain_all() selective

make lru_add_drain_all() only selectively interrupt the cpus that have
per-cpu free pages that can be drained.

This is important in nohz mode where calling mlockall(), for example,
otherwise will interrupt every core unnecessarily.

This is important on workloads where nohz cores are handling 10 Gb traffic
in userspace.  Those CPUs do not enter the kernel and place pages into LRU
pagevecs and they really, really don't want to be interrupted, or they
drop packets on the floor.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index c03c139219c9..46ba0c6c219f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -280,7 +280,7 @@ extern void activate_page(struct page *);
 extern void mark_page_accessed(struct page *);
 extern void lru_add_drain(void);
 extern void lru_add_drain_cpu(int cpu);
-extern int lru_add_drain_all(void);
+extern void lru_add_drain_all(void);
 extern void rotate_reclaimable_page(struct page *page);
 extern void deactivate_page(struct page *page);
 extern void swap_setup(void);