[PATCH v4 18/22] slab: refill sheaves from all nodes

Vlastimil Babka
2026-01-23T06:54:20Z

__refill_objects() currently only attempts to get partial slabs from the
local node and then allocates new slab(s). Expand it to trying also
other nodes while observing the remote node defrag ratio, similarly to
get_any_partial().

This will prevent allocating new slabs on a node while other nodes have
many free slabs. It does mean sheaves will contain non-local objects in
that case. Allocations that care about specific node will still be
served appropriately, but might get a slowpath allocation.

Like get_any_partial() we do observe cpuset_zone_allowed(), although we
might be refilling a sheaf that will be then used from a different
allocation context.

We can also use the resulting refill_objects() in
__kmem_cache_alloc_bulk() for non-debug caches. This means
kmem_cache_alloc_bulk() will get better performance when sheaves are
exhausted. kmem_cache_alloc_bulk() cannot indicate a preferred node so
it's compatible with sheaves refill in preferring the local node.
Its users also have gfp flags that allow spinning, so document that
as a requirement.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Hao Li <hao.li@linux.dev>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/slub.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 106 insertions(+), 31 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 1d135baf5e9e..540e3c641d1e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2512,8 +2512,8 @@ static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf)
}

static unsigned int
-__refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
- unsigned int max);
+refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
+ unsigned int max);

static int refill_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf,
gfp_t gfp)
@@ -2524,8 +2524,8 @@ static int refill_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf,
if (!to_fill)
return 0;

- filled = __refill_objects(s, &sheaf->objects[sheaf->size], gfp,
- to_fill, to_fill);
+ filled = refill_objects(s, &sheaf->objects[sheaf->size], gfp, to_fill,
+ to_fill);

sheaf->size += filled;

@@ -6550,29 +6550,22 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
EXPORT_SYMBOL(kmem_cache_free_bulk);

static unsigned int
-__refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
- unsigned int max)
+__refill_objects_node(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
+ unsigned int max, struct kmem_cache_node *n)
{
struct partial_bulk_context pc;
struct slab *slab, *slab2;
unsigned int refilled = 0;
unsigned long flags;
void *object;
- int node;

pc.flags = gfp;
pc.min_objects = min;
pc.max_objects = max;

- node = numa_mem_id();
-
- if (WARN_ON_ONCE(!gfpflags_allow_spinning(gfp)))
+ if (!get_partial_node_bulk(s, n, &pc))
return 0;

- /* TODO: consider also other nodes? */
- if (!get_partial_node_bulk(s, get_node(s, node), &pc))
- goto new_slab;
-
list_for_each_entry_safe(slab, slab2, &pc.slabs, slab_list) {

list_del(&slab->slab_list);
@@ -6610,8 +6603,6 @@ __refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
}

if (unlikely(!list_empty(&pc.slabs))) {
- struct kmem_cache_node *n = get_node(s, node);
-
spin_lock_irqsave(&n->list_lock, flags);

list_for_each_entry_safe(slab, slab2, &pc.slabs, slab_list) {
@@ -6633,13 +6624,92 @@ __refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
}
}

+ return refilled;
+}

- if (likely(refilled >= min))
- goto out;
+#ifdef CONFIG_NUMA
+static unsigned int
+__refill_objects_any(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
+ unsigned int max)
+{
+ struct zonelist *zonelist;
+ struct zoneref *z;
+ struct zone *zone;
+ enum zone_type highest_zoneidx = gfp_zone(gfp);
+ unsigned int cpuset_mems_cookie;
+ unsigned int refilled = 0;
+
+ /* see get_from_any_partial() for the defrag ratio description */
+ if (!s->remote_node_defrag_ratio ||
+ get_cycles() % 1024 > s->remote_node_defrag_ratio)
+ return 0;
+
+ do {
+ cpuset_mems_cookie = read_mems_allowed_begin();
+ zonelist = node_zonelist(mempolicy_slab_node(), gfp);
+ for_each_zone_zonelist(zone, z, zonelist, highest_zoneidx) {
+ struct kmem_cache_node *n;
+ unsigned int r;
+
+ n = get_node(s, zone_to_nid(zone));
+
+ if (!n || !cpuset_zone_allowed(zone, gfp) ||
+ n->nr_partial <= s->min_partial)
+ continue;
+
+ r = __refill_objects_node(s, p, gfp, min, max, n);
+ refilled += r;
+
+ if (r >= min) {
+ /*
+ * Don't check read_mems_allowed_retry() here -
+ * if mems_allowed was updated in parallel, that
+ * was a harmless race between allocation and
+ * the cpuset update
+ */
+ return refilled;
+ }
+ p += r;
+ min -= r;
+ max -= r;
+ }
+ } while (read_mems_allowed_retry(cpuset_mems_cookie));
+
+ return refilled;
+}
+#else
+static inline unsigned int
+__refill_objects_any(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
+ unsigned int max)
+{
+ return 0;
+}
+#endif
+
+static unsigned int
+refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,
+ unsigned int max)
+{
+ int local_node = numa_mem_id();
+ unsigned int refilled;
+ struct slab *slab;
+
+ if (WARN_ON_ONCE(!gfpflags_allow_spinning(gfp)))
+ return 0;
+
+ refilled = __refill_objects_node(s, p, gfp, min, max,
+ get_node(s, local_node));
+ if (refilled >= min)
+ return refilled;
+
+ refilled += __refill_objects_any(s, p + refilled, gfp, min - refilled,
+ max - refilled);
+ if (refilled >= min)
+ return refilled;

new_slab:

- slab = new_slab(s, pc.flags, node);
+ slab = new_slab(s, gfp, local_node);
if (!slab)
goto out;

@@ -6654,8 +6724,8 @@ __refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min,

if (refilled < min)
goto new_slab;
-out:

+out:
return refilled;
}

@@ -6665,18 +6735,20 @@ int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
{
int i;

- /*
- * TODO: this might be more efficient (if necessary) by reusing
- * __refill_objects()
- */
- for (i = 0; i < size; i++) {
+ if (IS_ENABLED(CONFIG_SLUB_TINY) || kmem_cache_debug(s)) {
+ for (i = 0; i < size; i++) {

- p[i] = ___slab_alloc(s, flags, NUMA_NO_NODE, _RET_IP_,
- s->object_size);
- if (unlikely(!p[i]))
- goto error;
+ p[i] = ___slab_alloc(s, flags, NUMA_NO_NODE, _RET_IP_,
+ s->object_size);
+ if (unlikely(!p[i]))
+ goto error;

- maybe_wipe_obj_freeptr(s, p[i]);
+ maybe_wipe_obj_freeptr(s, p[i]);
+ }
+ } else {
+ i = refill_objects(s, p, flags, size, size);
+ if (i < size)
+ goto error;
}

return i;
@@ -6687,7 +6759,10 @@ int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,

}

-/* Note that interrupts must be enabled when calling this function. */
+/*
+ * Note that interrupts must be enabled when calling this function and gfp
+ * flags must allow spinning.
+ */
int kmem_cache_alloc_bulk_noprof(struct kmem_cache *s, gfp_t flags, size_t size,
void **p)
{

--
2.52.0