[PATCH v3 08/21] slab: handle kmalloc sheaves bootstrap

Vlastimil Babka
2026-01-16T14:41:20Z

Enable sheaves for kmalloc caches. For other types than KMALLOC_NORMAL,
we can simply allow them in calculate_sizes() as they are created later
than KMALLOC_NORMAL caches and can allocate sheaves and barns from
those.

For KMALLOC_NORMAL caches we perform additional step after first
creating them without sheaves. Then bootstrap_cache_sheaves() simply
allocates and initializes barns and sheaves and finally sets
s->sheaf_capacity to make them actually used.

Afterwards the only caches left without sheaves (unless SLUB_TINY or
debugging is enabled) are kmem_cache and kmem_cache_node. These are only
used when creating or destroying other kmem_caches. Thus they are not
performance critical and we can simply leave it that way.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/slub.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 84 insertions(+), 4 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index b385247c219f..9bea8a65e510 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2605,7 +2605,8 @@ static void *setup_object(struct kmem_cache *s, void *object)
return object;
}

-static struct slab_sheaf *alloc_empty_sheaf(struct kmem_cache *s, gfp_t gfp)
+static struct slab_sheaf *__alloc_empty_sheaf(struct kmem_cache *s, gfp_t gfp,
+ unsigned int capacity)
{
struct slab_sheaf *sheaf;
size_t sheaf_size;
@@ -2623,7 +2624,7 @@ static struct slab_sheaf *alloc_empty_sheaf(struct kmem_cache *s, gfp_t gfp)
if (s->flags & SLAB_KMALLOC)
gfp |= __GFP_NO_OBJ_EXT;

- sheaf_size = struct_size(sheaf, objects, s->sheaf_capacity);
+ sheaf_size = struct_size(sheaf, objects, capacity);
sheaf = kzalloc(sheaf_size, gfp);

if (unlikely(!sheaf))
@@ -2636,6 +2637,12 @@ static struct slab_sheaf *alloc_empty_sheaf(struct kmem_cache *s, gfp_t gfp)
return sheaf;
}

+static inline struct slab_sheaf *alloc_empty_sheaf(struct kmem_cache *s,
+ gfp_t gfp)
+{
+ return __alloc_empty_sheaf(s, gfp, s->sheaf_capacity);
+}
+
static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf)
{
kfree(sheaf);
@@ -8119,8 +8126,11 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
if (s->flags & SLAB_RECLAIM_ACCOUNT)
s->allocflags |= __GFP_RECLAIMABLE;

- /* kmalloc caches need extra care to support sheaves */
- if (!is_kmalloc_cache(s))
+ /*
+ * For KMALLOC_NORMAL caches we enable sheaves later by
+ * bootstrap_kmalloc_sheaves() to avoid recursion
+ */
+ if (!is_kmalloc_normal(s))
s->sheaf_capacity = calculate_sheaf_capacity(s, args);

/*
@@ -8615,6 +8625,74 @@ static struct kmem_cache * __init bootstrap(struct kmem_cache *static_cache)
return s;
}

+/*
+ * Finish the sheaves initialization done normally by init_percpu_sheaves() and
+ * init_kmem_cache_nodes(). For normal kmalloc caches we have to bootstrap it
+ * since sheaves and barns are allocated by kmalloc.
+ */
+static void __init bootstrap_cache_sheaves(struct kmem_cache *s)
+{
+ struct kmem_cache_args empty_args = {};
+ unsigned int capacity;
+ bool failed = false;
+ int node, cpu;
+
+ capacity = calculate_sheaf_capacity(s, &empty_args);
+
+ /* capacity can be 0 due to debugging or SLUB_TINY */
+ if (!capacity)
+ return;
+
+ for_each_node_mask(node, slab_nodes) {
+ struct node_barn *barn;
+
+ barn = kmalloc_node(sizeof(*barn), GFP_KERNEL, node);
+
+ if (!barn) {
+ failed = true;
+ goto out;
+ }
+
+ barn_init(barn);
+ get_node(s, node)->barn = barn;
+ }
+
+ for_each_possible_cpu(cpu) {
+ struct slub_percpu_sheaves *pcs;
+
+ pcs = per_cpu_ptr(s->cpu_sheaves, cpu);
+
+ pcs->main = __alloc_empty_sheaf(s, GFP_KERNEL, capacity);
+
+ if (!pcs->main) {
+ failed = true;
+ break;
+ }
+ }
+
+out:
+ /*
+ * It's still early in boot so treat this like same as a failure to
+ * create the kmalloc cache in the first place
+ */
+ if (failed)
+ panic("Out of memory when creating kmem_cache %s\n", s->name);
+
+ s->sheaf_capacity = capacity;
+}
+
+static void __init bootstrap_kmalloc_sheaves(void)
+{
+ enum kmalloc_cache_type type;
+
+ for (type = KMALLOC_NORMAL; type <= KMALLOC_RANDOM_END; type++) {
+ for (int idx = 0; idx < KMALLOC_SHIFT_HIGH + 1; idx++) {
+ if (kmalloc_caches[type][idx])
+ bootstrap_cache_sheaves(kmalloc_caches[type][idx]);
+ }
+ }
+}
+
void __init kmem_cache_init(void)
{
static __initdata struct kmem_cache boot_kmem_cache,
@@ -8658,6 +8736,8 @@ void __init kmem_cache_init(void)
setup_kmalloc_cache_index_table();
create_kmalloc_caches();

+ bootstrap_kmalloc_sheaves();
+
/* Setup random freelists for each cache */
init_freelist_randomization();

--
2.52.0