[PATCH] mm/memcontrol: hoist pstatc_pcpu assignment out of CPU loop

[Hui Zhu]

From: Hui Zhu <zhuhui@xxxxxxxxxx>

In mem_cgroup_alloc(), the assignment of pstatc_pcpu is invariant
with respect to the for_each_possible_cpu() loop: both the 'parent'
pointer and 'parent->vmstats_percpu' remain constant throughout all
iterations.

The original code redundantly re-evaluated the 'if (parent)'
condition and reassigned pstatc_pcpu on every CPU iteration, then
repeated the same ternary check 'parent ? pstatc_pcpu : NULL' when
storing into statc->parent_pcpu.

Move the single conditional assignment of pstatc_pcpu to before the
loop, resolving both the loop-invariant placement issue and the
duplicated null check. On systems with a large number of possible
CPUs, this eliminates repeated branch evaluation with no functional
change.

No functional change intended.

Signed-off-by: Hui Zhu <zhuhui@xxxxxxxxxx>
---
 mm/memcontrol.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c3d98ab41f1f..4f4a60e57a08 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3993,11 +3993,10 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
 	if (!memcg1_alloc_events(memcg))
 		goto fail;
 
+	pstatc_pcpu = parent ? parent->vmstats_percpu : NULL;
 	for_each_possible_cpu(cpu) {
-		if (parent)
-			pstatc_pcpu = parent->vmstats_percpu;
 		statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
-		statc->parent_pcpu = parent ? pstatc_pcpu : NULL;
+		statc->parent_pcpu = pstatc_pcpu;
 		statc->vmstats = memcg->vmstats;
 	}
 
-- 
2.43.0