We can now use a this_cpu_cmpxchg_double to update two 64
bit values that are the entire description of the per cpu
freelist. There is no need anymore to disable preempt.
Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c 2014-12-09 12:31:45.867575731 -0600
+++ linux/mm/slub.c 2014-12-09 12:31:45.867575731 -0600
@@ -2272,21 +2272,15 @@ static inline void *get_freelist(struct
* a call to the page allocator and the setup of a new slab.
*/
static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
- unsigned long addr, struct kmem_cache_cpu *c)
+ unsigned long addr)
{
void *freelist;
struct page *page;
unsigned long flags;
+ struct kmem_cache_cpu *c;
local_irq_save(flags);
-#ifdef CONFIG_PREEMPT
- /*
- * We may have been preempted and rescheduled on a different
- * cpu before disabling interrupts. Need to reload cpu area
- * pointer.
- */
c = this_cpu_ptr(s->cpu_slab);
-#endif
if (!c->freelist || is_end_token(c->freelist))
goto new_slab;
@@ -2397,7 +2391,6 @@ static __always_inline void *slab_alloc_
gfp_t gfpflags, int node, unsigned long addr)
{
void **object;
- struct kmem_cache_cpu *c;
unsigned long tid;
if (slab_pre_alloc_hook(s, gfpflags))
@@ -2406,31 +2399,15 @@ static __always_inline void *slab_alloc_
s = memcg_kmem_get_cache(s, gfpflags);
redo:
/*
- * Must read kmem_cache cpu data via this cpu ptr. Preemption is
- * enabled. We may switch back and forth between cpus while
- * reading from one cpu area. That does not matter as long
- * as we end up on the original cpu again when doing the cmpxchg.
- *
- * Preemption is disabled for the retrieval of the tid because that
- * must occur from the current processor. We cannot allow rescheduling
- * on a different processor between the determination of the pointer
- * and the retrieval of the tid.
- */
- preempt_disable();
- c = this_cpu_ptr(s->cpu_slab);
-
- /*
* The transaction ids are globally unique per cpu and per operation on
* a per cpu queue. Thus they can be guarantee that the cmpxchg_double
* occurs on the right processor and that there was no operation on the
* linked list in between.
*/
- tid = c->tid;
- preempt_enable();
-
- object = c->freelist;
- if (unlikely(!object || is_end_token(object) ||!node_match_ptr(object, node))) {
- object = __slab_alloc(s, gfpflags, node, addr, c);
+ tid = this_cpu_read(s->cpu_slab->tid);
+ object = this_cpu_read(s->cpu_slab->freelist);
+ if (unlikely(!object || is_end_token(object) || !node_match_ptr(object, node))) {
+ object = __slab_alloc(s, gfpflags, node, addr);
stat(s, ALLOC_SLOWPATH);
} else {
void *next_object = get_freepointer_safe(s, object);
@@ -2666,30 +2643,21 @@ static __always_inline void slab_free(st
struct page *page, void *x, unsigned long addr)
{
void **object = (void *)x;
- struct kmem_cache_cpu *c;
+ void *freelist;
unsigned long tid;
slab_free_hook(s, x);
redo:
- /*
- * Determine the currently cpus per cpu slab.
- * The cpu may change afterward. However that does not matter since
- * data is retrieved via this pointer. If we are on the same cpu
- * during the cmpxchg then the free will succedd.
- */
- preempt_disable();
- c = this_cpu_ptr(s->cpu_slab);
-
- tid = c->tid;
- preempt_enable();
+ tid = this_cpu_read(s->cpu_slab->tid);
+ freelist = this_cpu_read(s->cpu_slab->freelist);
- if (likely(same_slab_page(s, page, c->freelist))) {
- set_freepointer(s, object, c->freelist);
+ if (likely(same_slab_page(s, page, freelist))) {
+ set_freepointer(s, object, freelist);
if (unlikely(!this_cpu_cmpxchg_double(
s->cpu_slab->freelist, s->cpu_slab->tid,
- c->freelist, tid,
+ freelist, tid,
object, next_tid(tid)))) {
note_cmpxchg_failure("slab_free", s, tid);
--
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