+#ifdef CONFIG_SMP
+/*
+ * Per cpu array for per cpu structures.
+ *
+ * The per cpu array places all kmem_cache_cpu structures from one processor
+ * close together meaning that it becomes possible that multiple per cpu
+ * structures are contained in one cacheline. This may be particularly
+ * beneficial for the kmalloc caches.
+ *
+ * A desktop system typically has around 60-80 slabs. With 100 here we are
+ * likely able to get per cpu structures for all caches from the array defined
+ * here. We must be able to cover all kmalloc caches during bootstrap.
+ *
+ * If the per cpu array is exhausted then fall back to kmalloc
+ * of individual cachelines. No sharing is possible then.
+ */
+#define NR_KMEM_CACHE_CPU 100
+
+static DEFINE_PER_CPU(struct kmem_cache_cpu,
+ kmem_cache_cpu)[NR_KMEM_CACHE_CPU];
+
+static DEFINE_PER_CPU(struct kmem_cache_cpu *, kmem_cache_cpu_free);
+static cpumask_t kmem_cach_cpu_free_init_once = CPU_MASK_NONE;
+
+static struct kmem_cache_cpu *alloc_kmem_cache_cpu(struct kmem_cache *s,
+ int cpu, gfp_t flags)
+{
+ struct kmem_cache_cpu *c = per_cpu(kmem_cache_cpu_free, cpu);
+
+ if (c)
+ per_cpu(kmem_cache_cpu_free, cpu) =
+ (void *)c->freelist;
+ else {
+ /* Table overflow: So allocate ourselves */
+ c = kmalloc_node(
+ ALIGN(sizeof(struct kmem_cache_cpu), cache_line_size()),
+ flags, cpu_to_node(cpu));
+ if (!c)
+ return NULL;
+ }
+
+ init_kmem_cache_cpu(s, c);
+ return c;
+}
+
+static void free_kmem_cache_cpu(struct kmem_cache_cpu *c, int cpu)
+{
+ if (c < per_cpu(kmem_cache_cpu, cpu) ||
+ c > per_cpu(kmem_cache_cpu, cpu) + NR_KMEM_CACHE_CPU) {
+ kfree(c);
+ return;
+ }
+ c->freelist = (void *)per_cpu(kmem_cache_cpu_free, cpu);
+ per_cpu(kmem_cache_cpu_free, cpu) = c;
+}
+
+static void free_kmem_cache_cpus(struct kmem_cache *s)
+{
+ int cpu;
+
+ for_each_online_cpu(cpu) {
+ struct kmem_cache_cpu *c = get_cpu_slab(s, cpu);
+
+ if (c) {
+ s->cpu_slab[cpu] = NULL;
+ free_kmem_cache_cpu(c, cpu);
+ }
+ }
+}
+
+static int alloc_kmem_cache_cpus(struct kmem_cache *s, gfp_t flags)
+{
+ int cpu;
+
+ for_each_online_cpu(cpu) {
+ struct kmem_cache_cpu *c = get_cpu_slab(s, cpu);
+
+ if (c)
+ continue;
+
+ c = alloc_kmem_cache_cpu(s, cpu, flags);
+ if (!c) {
+ free_kmem_cache_cpus(s);
+ return 0;
+ }
+ s->cpu_slab[cpu] = c;
+ }
+ return 1;
+}
+
+/*
+ * Initialize the per cpu array.
+ */
+static void init_alloc_cpu_cpu(int cpu)
+{
+ int i;
+
+ if (cpu_isset(cpu, kmem_cach_cpu_free_init_once))
+ return;
+
+ for (i = NR_KMEM_CACHE_CPU - 1; i >= 0; i--)
+ free_kmem_cache_cpu(&per_cpu(kmem_cache_cpu, cpu)[i], cpu);
+
+ cpu_set(cpu, kmem_cach_cpu_free_init_once);
+}
+
+static void __init init_alloc_cpu(void)
+{
+ int cpu;
+
+ for_each_online_cpu(cpu)
+ init_alloc_cpu_cpu(cpu);
+ }
+
+#else
+static inline void free_kmem_cache_cpus(struct kmem_cache *s) {}
+static inline void init_alloc_cpu(void) {}
+
+static inline int alloc_kmem_cache_cpus(struct kmem_cache *s, gfp_t flags)
+{
+ init_kmem_cache_cpu(s, &s->cpu_slab);
+ return 1;
+}
+#endif
+