[PATCH v2] mm/page_alloc: skip setting nodemask when we are in interrupt

[Muchun Song]

When we are in the interrupt context, it is irrelevant to the
current task context. If we use current task's mems_allowed, we
can fair to alloc pages in the fast path and fall back to slow
path memory allocation when the current node(which is the current
task mems_allowed) does not have enough memory to allocate. In
this case, it slows down the memory allocation speed of interrupt
context. So we can skip setting the nodemask to allow any node
to allocate memory, so that fast path allocation can success.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---

changelog in v2:
 1) rework the code suggested by Pekka Enberg
 2) add a comment

 mm/page_alloc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9808339a6e93b..6678c4c1c3087 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4799,7 +4799,11 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
 
 	if (cpusets_enabled()) {
 		*alloc_mask |= __GFP_HARDWALL;
-		if (!ac->nodemask)
+		/*
+		 * When we are in the interrupt context, it is irrelevant
+		 * to the current task context. It means that any node ok.
+		 */
+		if (!in_interrupt() && !ac->nodemask)
 			ac->nodemask = &cpuset_current_mems_allowed;
 		else
 			*alloc_flags |= ALLOC_CPUSET;
-- 
2.11.0