[RFC Patch 3/3] mm/slub: setup maxim per-node partial according to cpu numbers

[Feng Tang]

Currently most of the slab's min_partial is set to 5 (as MIN_PARTIAL
is 5). This is fine for older or small systesms, and could be too
small for a large system with hundreds of CPUs, when per-node
'list_lock' is contended for allocating from and freeing to per-node
partial list.

So enlarge it based on the CPU numbers per node.

Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
---
 include/linux/nodemask.h | 1 +
 mm/slub.c                | 9 +++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index 8d07116caaf1..6e22caab186d 100644
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -530,6 +530,7 @@ static inline int node_random(const nodemask_t *maskp)
 
 #define num_online_nodes()	num_node_state(N_ONLINE)
 #define num_possible_nodes()	num_node_state(N_POSSIBLE)
+#define num_cpu_nodes()		num_node_state(N_CPU)
 #define node_online(node)	node_state((node), N_ONLINE)
 #define node_possible(node)	node_state((node), N_POSSIBLE)
 
diff --git a/mm/slub.c b/mm/slub.c
index 09ae1ed642b7..984e012d7bbc 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4533,6 +4533,7 @@ static int calculate_sizes(struct kmem_cache *s)
 
 static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 {
+	unsigned long min_partial;
 	s->flags = kmem_cache_flags(s->size, flags, s->name);
 #ifdef CONFIG_SLAB_FREELIST_HARDENED
 	s->random = get_random_long();
@@ -4564,8 +4565,12 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 	 * The larger the object size is, the more slabs we want on the partial
 	 * list to avoid pounding the page allocator excessively.
 	 */
-	s->min_partial = min_t(unsigned long, MAX_PARTIAL, ilog2(s->size) / 2);
-	s->min_partial = max_t(unsigned long, MIN_PARTIAL, s->min_partial);
+
+	min_partial = rounddown_pow_of_two(num_cpus() / num_cpu_nodes());
+	min_partial = max_t(unsigned long, MIN_PARTIAL, min_partial);
+
+	s->min_partial = min_t(unsigned long, min_partial * 2, ilog2(s->size) / 2);
+	s->min_partial = max_t(unsigned long, min_partial, s->min_partial);
 
 	set_cpu_partial(s);
 
-- 
2.27.0