2009-10-07 22:05:24

by Christoph Lameter

Subject: [this_cpu_xx V6 4/7] SLUB: Get rid of dynamic DMA kmalloc cache allocation

Dynamic DMA kmalloc cache allocation is troublesome since the
new percpu allocator does not support allocations in atomic contexts.
Reserve some statically allocated kmalloc_cpu structures instead.

Signed-off-by: Christoph Lameter <[email protected]>

---
include/linux/slub_def.h | 19 +++++++++++--------
mm/slub.c | 24 ++++++++++--------------
2 files changed, 21 insertions(+), 22 deletions(-)

Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h 2009-09-29 11:42:06.000000000 -0500
+++ linux-2.6/include/linux/slub_def.h 2009-09-29 11:43:18.000000000 -0500
@@ -131,11 +131,21 @@ struct kmem_cache {

#define SLUB_PAGE_SHIFT (PAGE_SHIFT + 2)

+#ifdef CONFIG_ZONE_DMA
+#define SLUB_DMA __GFP_DMA
+/* Reserve extra caches for potential DMA use */
+#define KMALLOC_CACHES (2 * SLUB_PAGE_SHIFT - 6)
+#else
+/* Disable DMA functionality */
+#define SLUB_DMA (__force gfp_t)0
+#define KMALLOC_CACHES SLUB_PAGE_SHIFT
+#endif
+
/*
* We keep the general caches in an array of slab caches that are used for
* 2^x bytes of allocations.
*/
-extern struct kmem_cache kmalloc_caches[SLUB_PAGE_SHIFT];
+extern struct kmem_cache kmalloc_caches[KMALLOC_CACHES];

/*
* Sorry that the following has to be that ugly but some versions of GCC
@@ -203,13 +213,6 @@ static __always_inline struct kmem_cache
return &kmalloc_caches[index];
}

-#ifdef CONFIG_ZONE_DMA
-#define SLUB_DMA __GFP_DMA
-#else
-/* Disable DMA functionality */
-#define SLUB_DMA (__force gfp_t)0
-#endif
-
void *kmem_cache_alloc(struct kmem_cache *, gfp_t);
void *__kmalloc(size_t size, gfp_t flags);

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2009-09-29 11:42:06.000000000 -0500
+++ linux-2.6/mm/slub.c 2009-09-29 11:43:18.000000000 -0500
@@ -2090,7 +2090,7 @@ static inline int alloc_kmem_cache_cpus(
{
int cpu;

- if (s < kmalloc_caches + SLUB_PAGE_SHIFT && s >= kmalloc_caches)
+ if (s < kmalloc_caches + KMALLOC_CACHES && s >= kmalloc_caches)
/*
* Boot time creation of the kmalloc array. Use static per cpu data
* since the per cpu allocator is not available yet.
@@ -2537,7 +2537,7 @@ EXPORT_SYMBOL(kmem_cache_destroy);
* Kmalloc subsystem
*******************************************************************/

-struct kmem_cache kmalloc_caches[SLUB_PAGE_SHIFT] __cacheline_aligned;
+struct kmem_cache kmalloc_caches[KMALLOC_CACHES] __cacheline_aligned;
EXPORT_SYMBOL(kmalloc_caches);

static int __init setup_slub_min_order(char *str)
@@ -2627,6 +2627,7 @@ static noinline struct kmem_cache *dma_k
char *text;
size_t realsize;
unsigned long slabflags;
+ int i;

s = kmalloc_caches_dma[index];
if (s)
@@ -2647,18 +2648,13 @@ static noinline struct kmem_cache *dma_k
text = kasprintf(flags & ~SLUB_DMA, "kmalloc_dma-%d",
(unsigned int)realsize);

- if (flags & __GFP_WAIT)
- s = kmalloc(kmem_size, flags & ~SLUB_DMA);
- else {
- int i;
+ s = NULL;
+ for (i = 0; i < KMALLOC_CACHES; i++)
+ if (kmalloc_caches[i].size)
+ break;

- s = NULL;
- for (i = 0; i < SLUB_PAGE_SHIFT; i++)
- if (kmalloc_caches[i].size) {
- s = kmalloc_caches + i;
- break;
- }
- }
+ BUG_ON(i >= KMALLOC_CACHES);
+ s = kmalloc_caches + i;

/*
* Must defer sysfs creation to a workqueue because we don't know
@@ -2672,7 +2668,7 @@ static noinline struct kmem_cache *dma_k

if (!s || !text || !kmem_cache_open(s, flags, text,
realsize, ARCH_KMALLOC_MINALIGN, slabflags, NULL)) {
- kfree(s);
+ s->size = 0;
kfree(text);
goto unlock_out;
}

--

2009-10-13 18:56:36

by Christoph Lameter

Subject: [FIX] patch "SLUB: Get rid of dynamic DMA kmalloc cache allocation"

Slight bug when creating kmalloc dma caches on the fly. When searching for
an unused statically allocated kmem_cache structure we need to check for
size == 0 not the other way around.

Signed-off-by: Christoph Lameter <[email protected]>

---
mm/slub.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2009-10-13 13:31:05.000000000 -0500
+++ linux-2.6/mm/slub.c 2009-10-13 13:31:36.000000000 -0500
@@ -2650,7 +2650,7 @@ static noinline struct kmem_cache *dma_k

s = NULL;
for (i = 0; i < KMALLOC_CACHES; i++)
- if (kmalloc_caches[i].size)
+ if (!kmalloc_caches[i].size)
break;

BUG_ON(i >= KMALLOC_CACHES);