mm/slub: handle bulk and single object freeing separately

Currently we have a single function slab_free() handling both single
object freeing and bulk freeing with necessary hooks, the latter case
requiring slab_free_freelist_hook(). It should be however better to
distinguish the two use cases for the following reasons:

- code simpler to follow for the single object case

- better code generation - although inlining should eliminate the
  slab_free_freelist_hook() for single object freeing in case no
  debugging options are enabled, it seems it's not perfect. When e.g.
  KASAN is enabled, we're imposing additional unnecessary overhead for
  single object freeing.

- preparation to add percpu array caches in near future

Therefore, simplify slab_free() for the single object case by dropping
unnecessary parameters and calling only slab_free_hook() instead of
slab_free_freelist_hook(). Rename the bulk variant to slab_free_bulk()
and adjust callers accordingly.

While at it, flip (and document) slab_free_hook() return value so that
it returns true when the freeing can proceed, which matches the logic of
slab_free_freelist_hook() and is not confusingly the opposite.

Additionally we can simplify a bit by changing the tail parameter of
do_slab_free() when freeing a single object - instead of NULL we can set
it equal to head.

bloat-o-meter shows small code reduction with a .config that has KASAN
etc disabled:

add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-118 (-118)
Function                                     old     new   delta
kmem_cache_alloc_bulk                       1203    1196      -7
kmem_cache_free                              861     835     -26
__kmem_cache_free                            741     704     -37
kmem_cache_free_bulk                         911     863     -48

Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

diff --git a/mm/slub.c b/mm/slub.c
index 0a9e4bd0dd6857100519fe5963098e0fa5a47d77..af8c8fc9e799bd955913d627b379977426ad7bc4 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2051,9 +2051,12 @@ void memcg_slab_alloc_error_hook(struct kmem_cache *s, int objects,
 /*
  * Hooks for other subsystems that check memory allocations. In a typical
  * production configuration these hooks all should produce no code at all.
+ *
+ * Returns true if freeing of the object can proceed, false if its reuse
+ * was delayed by KASAN quarantine.
  */
-static __always_inline bool slab_free_hook(struct kmem_cache *s,
-                                               void *x, bool init)
+static __always_inline
+bool slab_free_hook(struct kmem_cache *s, void *x, bool init)
 {
        kmemleak_free_recursive(x, s->flags);
        kmsan_slab_free(s, x);
@@ -2086,7 +2089,7 @@ static __always_inline bool slab_free_hook(struct kmem_cache *s,
                       s->size - s->inuse - rsize);
        }
        /* KASAN might put x into memory quarantine, delaying its reuse. */
-       return kasan_slab_free(s, x, init);
+       return !kasan_slab_free(s, x, init);
 }
 
 static inline bool slab_free_freelist_hook(struct kmem_cache *s,
@@ -2096,7 +2099,7 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
 
        void *object;
        void *next = *head;
-       void *old_tail = *tail ? *tail : *head;
+       void *old_tail = *tail;
 
        if (is_kfence_address(next)) {
                slab_free_hook(s, next, false);
@@ -2112,8 +2115,8 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
                next = get_freepointer(s, object);
 
                /* If object's reuse doesn't have to be delayed */
-               if (likely(!slab_free_hook(s, object,
-                                          slab_want_init_on_free(s)))) {
+               if (likely(slab_free_hook(s, object,
+                                         slab_want_init_on_free(s)))) {
                        /* Move object to the new freelist */
                        set_freepointer(s, object, *head);
                        *head = object;
@@ -2128,9 +2131,6 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
                }
        } while (object != old_tail);
 
-       if (*head == *tail)
-               *tail = NULL;
-
        return *head != NULL;
 }
 
@@ -4241,7 +4241,6 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
                                struct slab *slab, void *head, void *tail,
                                int cnt, unsigned long addr)
 {
-       void *tail_obj = tail ? : head;
        struct kmem_cache_cpu *c;
        unsigned long tid;
        void **freelist;
@@ -4260,14 +4259,14 @@ redo:
        barrier();
 
        if (unlikely(slab != c->slab)) {
-               __slab_free(s, slab, head, tail_obj, cnt, addr);
+               __slab_free(s, slab, head, tail, cnt, addr);
                return;
        }
 
        if (USE_LOCKLESS_FAST_PATH()) {
                freelist = READ_ONCE(c->freelist);
 
-               set_freepointer(s, tail_obj, freelist);
+               set_freepointer(s, tail, freelist);
 
                if (unlikely(!__update_cpu_freelist_fast(s, freelist, head, tid))) {
                        note_cmpxchg_failure("slab_free", s, tid);
@@ -4284,7 +4283,7 @@ redo:
                tid = c->tid;
                freelist = c->freelist;
 
-               set_freepointer(s, tail_obj, freelist);
+               set_freepointer(s, tail, freelist);
                c->freelist = head;
                c->tid = next_tid(tid);
 
@@ -4297,15 +4296,27 @@ static void do_slab_free(struct kmem_cache *s,
                                struct slab *slab, void *head, void *tail,
                                int cnt, unsigned long addr)
 {
-       void *tail_obj = tail ? : head;
-
-       __slab_free(s, slab, head, tail_obj, cnt, addr);
+       __slab_free(s, slab, head, tail, cnt, addr);
 }
 #endif /* CONFIG_SLUB_TINY */
 
-static __fastpath_inline void slab_free(struct kmem_cache *s, struct slab *slab,
-                                     void *head, void *tail, void **p, int cnt,
-                                     unsigned long addr)
+static __fastpath_inline
+void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
+              unsigned long addr)
+{
+       bool init;
+
+       memcg_slab_free_hook(s, slab, &object, 1);
+
+       init = !is_kfence_address(object) && slab_want_init_on_free(s);
+
+       if (likely(slab_free_hook(s, object, init)))
+               do_slab_free(s, slab, object, object, 1, addr);
+}
+
+static __fastpath_inline
+void slab_free_bulk(struct kmem_cache *s, struct slab *slab, void *head,
+                   void *tail, void **p, int cnt, unsigned long addr)
 {
        memcg_slab_free_hook(s, slab, p, cnt);
        /*
@@ -4319,7 +4330,7 @@ static __fastpath_inline void slab_free(struct kmem_cache *s, struct slab *slab,
 #ifdef CONFIG_KASAN_GENERIC
 void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr)
 {
-       do_slab_free(cache, virt_to_slab(x), x, NULL, 1, addr);
+       do_slab_free(cache, virt_to_slab(x), x, x, 1, addr);
 }
 #endif
 
@@ -4363,7 +4374,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
        if (!s)
                return;
        trace_kmem_cache_free(_RET_IP_, x, s);
-       slab_free(s, virt_to_slab(x), x, NULL, &x, 1, _RET_IP_);
+       slab_free(s, virt_to_slab(x), x, _RET_IP_);
 }
 EXPORT_SYMBOL(kmem_cache_free);
 
@@ -4409,7 +4420,7 @@ void kfree(const void *object)
 
        slab = folio_slab(folio);
        s = slab->slab_cache;
-       slab_free(s, slab, x, NULL, &x, 1, _RET_IP_);
+       slab_free(s, slab, x, _RET_IP_);
 }
 EXPORT_SYMBOL(kfree);
 
@@ -4526,8 +4537,8 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
                if (!df.slab)
                        continue;
 
-               slab_free(df.s, df.slab, df.freelist, df.tail, &p[size], df.cnt,
-                         _RET_IP_);
+               slab_free_bulk(df.s, df.slab, df.freelist, df.tail, &p[size],
+                              df.cnt, _RET_IP_);
        } while (likely(size));
 }
 EXPORT_SYMBOL(kmem_cache_free_bulk);