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

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Date:	Wed, 25 Aug 2010 09:07:07 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: Re: linux-next: build failure after merge of the final tree (slab
 tree related)

On Wed, 25 Aug 2010, Pekka Enberg wrote:

> I dropped slub cleanups from -next until we've resolved the UP boot time crash
> problem.
>

It works here with this patch. I'd rather see a general solution so that
we can use allocpercpu for bootstrapping any allocator without such
special bandaids.



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.

Signed-off-by: Christoph Lameter <cl@...ux.com>

---
 mm/slub.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2010-08-24 20:07:12.766010774 -0500
+++ linux-2.6/mm/slub.c	2010-08-24 20:15:46.304130417 -0500
@@ -2064,8 +2064,24 @@

 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 *)__get_free_page(GFP_NOWAIT, 1);
+	else
+#endif

 	s->cpu_slab = alloc_percpu(struct kmem_cache_cpu);

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