Slub: UP bandaid

Since the percpu allocator does not provide early allocation in UP mode (only
in SMP configurations) use __get_free_page() to improvise a compound page
allocation that can be later freed via kfree().

Compound pages will be released when the cpu caches are resized.
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slub.c

@@ -2103,8 +2103,24 @@ init_kmem_cache_node(struct kmem_cache_node *n, struct kmem_cache *s)
 
 static inline int alloc_kmem_cache_cpus(struct kmem_cache *s)
 {
+#ifdef CONFIG_SMP
+	/*
+	 * Will use reserve that does not require slab operation during
+	 * early boot.
+	 */
 	BUILD_BUG_ON(PERCPU_DYNAMIC_EARLY_SIZE <
 			SLUB_PAGE_SHIFT * sizeof(struct kmem_cache_cpu));
+#else
+	/*
+	 * Special hack for UP mode. allocpercpu() falls back to kmalloc
+	 * operations. So we cannot use that before the slab allocator is up
+	 * Simply get the smallest possible compound page. The page will be
+	 * released via kfree() when the cpu caches are resized later.
+	 */
+	if (slab_state < UP)
+		s->cpu_slab = (__percpu void *)kmalloc_large(PAGE_SIZE << 1, GFP_NOWAIT);
+	else
+#endif
 
 	s->cpu_slab = alloc_percpu(struct kmem_cache_cpu);