From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Since the introduce of unfrozen slabs on cpu partial list, we don't
need to synchronize the slab frozen state under the node list_lock.
The caller of deactivate_slab() and the caller of __slab_free() won't
manipulate the slab list concurrently.
So we can get node list_lock in the last stage if we really need to
manipulate the slab list in this path.
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
mm/slub.c | 76 +++++++++++++++++++------------------------------------
1 file changed, 26 insertions(+), 50 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index bcb5b2c4e213..c429f8baba5f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2468,10 +2468,8 @@ static void init_kmem_cache_cpus(struct kmem_cache *s)
static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
void *freelist)
{
- enum slab_modes { M_NONE, M_PARTIAL, M_FREE, M_FULL_NOLIST };
struct kmem_cache_node *n = get_node(s, slab_nid(slab));
int free_delta = 0;
- enum slab_modes mode = M_NONE;
void *nextfree, *freelist_iter, *freelist_tail;
int tail = DEACTIVATE_TO_HEAD;
unsigned long flags = 0;
@@ -2512,62 +2510,40 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
*
* Ensure that the slab is unfrozen while the list presence
* reflects the actual number of objects during unfreeze.
- *
- * We first perform cmpxchg holding lock and insert to list
- * when it succeed. If there is mismatch then the slab is not
- * unfrozen and number of objects in the slab may have changed.
- * Then release lock and retry cmpxchg again.
*/
-redo:
-
- old.freelist = READ_ONCE(slab->freelist);
- old.counters = READ_ONCE(slab->counters);
- VM_BUG_ON(!old.frozen);
-
- /* Determine target state of the slab */
- new.counters = old.counters;
- if (freelist_tail) {
- new.inuse -= free_delta;
- set_freepointer(s, freelist_tail, old.freelist);
- new.freelist = freelist;
- } else
- new.freelist = old.freelist;
-
- new.frozen = 0;
+ do {
+ old.freelist = READ_ONCE(slab->freelist);
+ old.counters = READ_ONCE(slab->counters);
+ VM_BUG_ON(!old.frozen);
+
+ /* Determine target state of the slab */
+ new.counters = old.counters;
+ new.frozen = 0;
+ if (freelist_tail) {
+ new.inuse -= free_delta;
+ set_freepointer(s, freelist_tail, old.freelist);
+ new.freelist = freelist;
+ } else {
+ new.freelist = old.freelist;
+ }
+ } while (!slab_update_freelist(s, slab,
+ old.freelist, old.counters,
+ new.freelist, new.counters,
+ "unfreezing slab"));
+ /*
+ * Stage three: Manipulate the slab list based on the updated state.
+ */
if (!new.inuse && n->nr_partial >= s->min_partial) {
- mode = M_FREE;
+ stat(s, DEACTIVATE_EMPTY);
+ discard_slab(s, slab);
+ stat(s, FREE_SLAB);
} else if (new.freelist) {
- mode = M_PARTIAL;
- /*
- * Taking the spinlock removes the possibility that
- * acquire_slab() will see a slab that is frozen
- */
spin_lock_irqsave(&n->list_lock, flags);
- } else {
- mode = M_FULL_NOLIST;
- }
-
-
- if (!slab_update_freelist(s, slab,
- old.freelist, old.counters,
- new.freelist, new.counters,
- "unfreezing slab")) {
- if (mode == M_PARTIAL)
- spin_unlock_irqrestore(&n->list_lock, flags);
- goto redo;
- }
-
-
- if (mode == M_PARTIAL) {
add_partial(n, slab, tail);
spin_unlock_irqrestore(&n->list_lock, flags);
stat(s, tail);
- } else if (mode == M_FREE) {
- stat(s, DEACTIVATE_EMPTY);
- discard_slab(s, slab);
- stat(s, FREE_SLAB);
- } else if (mode == M_FULL_NOLIST) {
+ } else {
stat(s, DEACTIVATE_FULL);
}
}
--
2.20.1
