Re: [PATCH v4 09/22] slab: handle kmalloc sheaves bootstrap

Liam R. Howlett
2026-01-27T18:31:16Z

* Vlastimil Babka <vbabka@suse.cz> [260123 01:53]:
> 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: Harry Yoo <harry.yoo@oracle.com>
> Reviewed-by: Hao Li <hao.li@linux.dev>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
> mm/slub.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 84 insertions(+), 4 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 4ca6bd944854..22acc249f9c0 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2593,7 +2593,8 @@ 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;
> @@ -2611,7 +2612,7 @@ 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))
> @@ -2624,6 +2625,12 @@ 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);
> @@ -8144,8 +8151,11 @@ 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);
>
> /*
> @@ -8640,6 +8650,74 @@ 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,
> @@ -8683,6 +8761,8 @@ 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
>