We touch a cacheline in the kmem_cache structure for zeroing to get the
size. However, the hot paths in slab_alloc and slab_free do not reference
any other fields in kmem_cache.
Add a new field to kmem_cache_cpu that contains the object size. That
cacheline must already be used. So we save one cacheline on every
slab_alloc.
We need to update the kmem_cache_cpu object size if an aliasing operation
changes the objsize of an non debug slab.
Signed-off-by: Christoph Lameter <[email protected]>
---
include/linux/slub_def.h | 1 +
mm/slub.c | 14 ++++++++++++--
2 files changed, 13 insertions(+), 2 deletions(-)
Index: linux-2.6.22-rc6-mm1/include/linux/slub_def.h
===================================================================
--- linux-2.6.22-rc6-mm1.orig/include/linux/slub_def.h 2007-07-07 13:56:24.000000000 -0700
+++ linux-2.6.22-rc6-mm1/include/linux/slub_def.h 2007-07-07 15:52:37.000000000 -0700
@@ -16,6 +16,7 @@ struct kmem_cache_cpu {
struct page *page;
int node;
unsigned int offset;
+ unsigned int objsize;
};
struct kmem_cache_node {
Index: linux-2.6.22-rc6-mm1/mm/slub.c
===================================================================
--- linux-2.6.22-rc6-mm1.orig/mm/slub.c 2007-07-07 13:56:24.000000000 -0700
+++ linux-2.6.22-rc6-mm1/mm/slub.c 2007-07-07 17:49:25.000000000 -0700
@@ -1571,7 +1571,7 @@ static void __always_inline *slab_alloc(
local_irq_restore(flags);
if (unlikely((gfpflags & __GFP_ZERO) && object))
- memset(object, 0, s->objsize);
+ memset(object, 0, c->objsize);
return object;
}
@@ -1864,8 +1864,9 @@ static void init_kmem_cache_cpu(struct k
{
c->page = NULL;
c->freelist = NULL;
- c->offset = s->offset / sizeof(void *);
c->node = 0;
+ c->offset = s->offset / sizeof(void *);
+ c->objsize = s->objsize;
}
static void init_kmem_cache_node(struct kmem_cache_node *n)
@@ -3173,12 +3174,21 @@ struct kmem_cache *kmem_cache_create(con
down_write(&slub_lock);
s = find_mergeable(size, align, flags, ctor, ops);
if (s) {
+ int cpu;
+
s->refcount++;
/*
* Adjust the object sizes so that we clear
* the complete object on kzalloc.
*/
s->objsize = max(s->objsize, (int)size);
+
+ /*
+ * And then we need to update the object size in the
+ * per cpu structures
+ */
+ for_each_online_cpu(cpu)
+ get_cpu_slab(s, cpu)->objsize = s->objsize;
s->inuse = max_t(int, s->inuse, ALIGN(size, sizeof(void *)));
up_write(&slub_lock);
--
-
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