Re: linux-next: build failure after merge of the final tree (slab tree related)

[Christoph Lameter <cl@linux.com>]

On Wed, 25 Aug 2010, David Rientjes wrote:

> I'm really hoping that we can remove this hack soon when the percpu
> allocator can handle these allocations on UP without any specialized slab
> behavior.

So do I. Here is a slightly less hacky version through using
kmalloc_large instead:


Subject: 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>
---
 mm/slub.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2010-08-26 09:19:35.000000000 -0500
+++ linux-2.6/mm/slub.c	2010-08-26 09:36:29.000000000 -0500
@@ -2103,8 +2103,24 @@ init_kmem_cache_node(struct kmem_cache_n

 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);