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slub: Delay freezing of partial slabs
Now we will freeze slabs when moving them out of node partial list to cpu partial list, this method needs two cmpxchg_double operations: 1. freeze slab (acquire_slab()) under the node list_lock 2. get_freelist() when pick used in ___slab_alloc() Actually we don't need to freeze when moving slabs out of node partial list, we can delay freezing to when use slab freelist in ___slab_alloc(), so we can save one cmpxchg_double(). And there are other good points: - The moving of slabs between node partial list and cpu partial list becomes simpler, since we don't need to freeze or unfreeze at all. - The node list_lock contention would be less, since we don't need to freeze any slab under the node list_lock. We can achieve this because there is no concurrent path would manipulate the partial slab list except the __slab_free() path, which is now serialized by slab_test_node_partial() under the list_lock. Since the slab returned by get_partial() interfaces is not frozen anymore and no freelist is returned in the partial_context, so we need to use the introduced freeze_slab() to freeze it and get its freelist. Similarly, the slabs on the CPU partial list are not frozen anymore, we need to freeze_slab() on it before use. We can now delete acquire_slab() as it became unused. Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
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213094b5d1
commit
8cd3fa428b
115
mm/slub.c
115
mm/slub.c
@ -2166,7 +2166,7 @@ static inline void remove_partial(struct kmem_cache_node *n,
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}
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/*
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* Called only for kmem_cache_debug() caches instead of acquire_slab(), with a
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* Called only for kmem_cache_debug() caches instead of remove_partial(), with a
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* slab from the n->partial list. Remove only a single object from the slab, do
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* the alloc_debug_processing() checks and leave the slab on the list, or move
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* it to full list if it was the last free object.
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@ -2234,51 +2234,6 @@ static void *alloc_single_from_new_slab(struct kmem_cache *s,
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return object;
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}
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/*
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* Remove slab from the partial list, freeze it and
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* return the pointer to the freelist.
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*
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* Returns a list of objects or NULL if it fails.
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*/
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static inline void *acquire_slab(struct kmem_cache *s,
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struct kmem_cache_node *n, struct slab *slab,
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int mode)
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{
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void *freelist;
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unsigned long counters;
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struct slab new;
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lockdep_assert_held(&n->list_lock);
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/*
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* Zap the freelist and set the frozen bit.
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* The old freelist is the list of objects for the
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* per cpu allocation list.
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*/
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freelist = slab->freelist;
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counters = slab->counters;
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new.counters = counters;
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if (mode) {
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new.inuse = slab->objects;
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new.freelist = NULL;
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} else {
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new.freelist = freelist;
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}
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VM_BUG_ON(new.frozen);
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new.frozen = 1;
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if (!__slab_update_freelist(s, slab,
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freelist, counters,
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new.freelist, new.counters,
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"acquire_slab"))
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return NULL;
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remove_partial(n, slab);
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WARN_ON(!freelist);
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return freelist;
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}
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#ifdef CONFIG_SLUB_CPU_PARTIAL
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static void put_cpu_partial(struct kmem_cache *s, struct slab *slab, int drain);
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#else
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@ -2295,7 +2250,6 @@ static struct slab *get_partial_node(struct kmem_cache *s,
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struct partial_context *pc)
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{
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struct slab *slab, *slab2, *partial = NULL;
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void *object = NULL;
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unsigned long flags;
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unsigned int partial_slabs = 0;
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@ -2314,7 +2268,7 @@ static struct slab *get_partial_node(struct kmem_cache *s,
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continue;
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if (IS_ENABLED(CONFIG_SLUB_TINY) || kmem_cache_debug(s)) {
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object = alloc_single_from_partial(s, n, slab,
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void *object = alloc_single_from_partial(s, n, slab,
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pc->orig_size);
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if (object) {
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partial = slab;
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@ -2324,13 +2278,10 @@ static struct slab *get_partial_node(struct kmem_cache *s,
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continue;
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}
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object = acquire_slab(s, n, slab, object == NULL);
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if (!object)
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break;
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remove_partial(n, slab);
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if (!partial) {
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partial = slab;
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pc->object = object;
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stat(s, ALLOC_FROM_PARTIAL);
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} else {
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put_cpu_partial(s, slab, 0);
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@ -2629,9 +2580,6 @@ static void __unfreeze_partials(struct kmem_cache *s, struct slab *partial_slab)
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unsigned long flags = 0;
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while (partial_slab) {
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struct slab new;
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struct slab old;
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slab = partial_slab;
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partial_slab = slab->next;
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@ -2644,23 +2592,7 @@ static void __unfreeze_partials(struct kmem_cache *s, struct slab *partial_slab)
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spin_lock_irqsave(&n->list_lock, flags);
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}
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do {
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old.freelist = slab->freelist;
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old.counters = slab->counters;
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VM_BUG_ON(!old.frozen);
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new.counters = old.counters;
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new.freelist = old.freelist;
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new.frozen = 0;
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} while (!__slab_update_freelist(s, slab,
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old.freelist, old.counters,
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new.freelist, new.counters,
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"unfreezing slab"));
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if (unlikely(!new.inuse && n->nr_partial >= s->min_partial)) {
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if (unlikely(!slab->inuse && n->nr_partial >= s->min_partial)) {
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slab->next = slab_to_discard;
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slab_to_discard = slab;
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} else {
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@ -3167,7 +3099,6 @@ reread_slab:
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node = NUMA_NO_NODE;
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goto new_slab;
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}
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redo:
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if (unlikely(!node_match(slab, node))) {
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/*
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@ -3243,7 +3174,8 @@ deactivate_slab:
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new_slab:
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if (slub_percpu_partial(c)) {
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#ifdef CONFIG_SLUB_CPU_PARTIAL
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while (slub_percpu_partial(c)) {
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local_lock_irqsave(&s->cpu_slab->lock, flags);
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if (unlikely(c->slab)) {
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local_unlock_irqrestore(&s->cpu_slab->lock, flags);
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@ -3255,12 +3187,22 @@ new_slab:
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goto new_objects;
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}
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slab = c->slab = slub_percpu_partial(c);
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slab = slub_percpu_partial(c);
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slub_set_percpu_partial(c, slab);
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local_unlock_irqrestore(&s->cpu_slab->lock, flags);
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stat(s, CPU_PARTIAL_ALLOC);
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goto redo;
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if (unlikely(!node_match(slab, node) ||
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!pfmemalloc_match(slab, gfpflags))) {
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slab->next = NULL;
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__unfreeze_partials(s, slab);
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continue;
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}
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freelist = freeze_slab(s, slab);
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goto retry_load_slab;
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}
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#endif
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new_objects:
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@ -3268,8 +3210,8 @@ new_objects:
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pc.orig_size = orig_size;
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slab = get_partial(s, node, &pc);
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if (slab) {
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freelist = pc.object;
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if (kmem_cache_debug(s)) {
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freelist = pc.object;
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/*
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* For debug caches here we had to go through
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* alloc_single_from_partial() so just store the
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@ -3281,6 +3223,7 @@ new_objects:
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return freelist;
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}
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freelist = freeze_slab(s, slab);
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goto retry_load_slab;
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}
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@ -3682,18 +3625,8 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
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was_frozen = new.frozen;
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new.inuse -= cnt;
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if ((!new.inuse || !prior) && !was_frozen) {
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if (kmem_cache_has_cpu_partial(s) && !prior) {
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/*
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* Slab was on no list before and will be
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* partially empty
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* We can defer the list move and instead
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* freeze it.
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*/
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new.frozen = 1;
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} else { /* Needs to be taken off a list */
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/* Needs to be taken off a list */
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if (!kmem_cache_has_cpu_partial(s) || prior) {
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n = get_node(s, slab_nid(slab));
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/*
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@ -3723,9 +3656,9 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
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* activity can be necessary.
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*/
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stat(s, FREE_FROZEN);
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} else if (new.frozen) {
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} else if (kmem_cache_has_cpu_partial(s) && !prior) {
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/*
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* If we just froze the slab then put it onto the
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* If we started with a full slab then put it onto the
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* per cpu partial list.
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*/
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put_cpu_partial(s, slab, 1);
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