[RFC 07/26] SLUB: Sort slab cache list and establish maximum objects for defrag slabs

[Christoph Lameter]

When we defragmenting slabs then it is advantageous to have all
defragmentable slabs together at the beginning of the list so that we do not
have to scan the complete list. When adding a slab cache put defragmentale
caches first and others last.

Determine the maximum number of objects in defragmentable slabs. This allows
to size the allocation of arrays holding refs to these objects later.

Signed-off-by: Christoph Lameter <clameter@xxxxxxx>
---
 mm/slub.c |   19 +++++++++++++++++--
 1 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 4a64038..9006069 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -226,6 +226,9 @@ static enum {
 static DECLARE_RWSEM(slub_lock);
 static LIST_HEAD(slab_caches);
 
+/* Maximum objects in defragmentable slabs */
+static unsigned int max_defrag_slab_objects = 0;
+
 /*
  * Tracking user of a slab.
  */
@@ -2385,7 +2388,7 @@ static struct kmem_cache *create_kmalloc_cache(struct kmem_cache *s,
 			flags, NULL))
 		goto panic;
 
-	list_add(&s->list, &slab_caches);
+	list_add_tail(&s->list, &slab_caches);
 	up_write(&slub_lock);
 	if (sysfs_slab_add(s))
 		goto panic;
@@ -2597,6 +2600,13 @@ void kfree(const void *x)
 }
 EXPORT_SYMBOL(kfree);
 
+static inline void *alloc_scratch(void)
+{
+	return kmalloc(max_defrag_slab_objects * sizeof(void *) +
+	    BITS_TO_LONGS(max_defrag_slab_objects) * sizeof(unsigned long),
+								GFP_KERNEL);
+}
+
 void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private))
@@ -2608,6 +2618,11 @@ void kmem_cache_setup_defrag(struct kmem_cache *s,
 	BUG_ON(!s->ctor);
 	s->get = get;
 	s->kick = kick;
+	down_write(&slub_lock);
+	list_move(&s->list, &slab_caches);
+	if (s->objects > max_defrag_slab_objects)
+		max_defrag_slab_objects = s->objects;
+	up_write(&slub_lock);
 }
 EXPORT_SYMBOL(kmem_cache_setup_defrag);
 
@@ -2878,7 +2893,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 	if (s) {
 		if (kmem_cache_open(s, GFP_KERNEL, name,
 				size, align, flags, ctor)) {
-			list_add(&s->list, &slab_caches);
+			list_add_tail(&s->list, &slab_caches);
 			up_write(&slub_lock);
 			if (sysfs_slab_add(s))
 				goto err;
-- 
1.5.2.4

-- 
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