[PATCH RFC v3 3/9] mm/slub: handle bulk and single object freeing separately
Vlastimil Babka
vbabka at suse.cz
Wed Nov 29 01:53:28 PST 2023
Until now we have a single function slab_free() handling both single
object freeing and bulk freeing with neccessary hooks, the latter case
requiring slab_free_freelist_hook(). It should be however better to
distinguish the two scenarios 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() 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 later patches
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
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
Signed-off-by: Vlastimil Babka <vbabka at suse.cz>
---
mm/slub.c | 57 ++++++++++++++++++++++++++++++++++-----------------------
1 file changed, 34 insertions(+), 23 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 16748aeada8f..7d23f10d42e6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1770,9 +1770,12 @@ static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
/*
* 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);
@@ -1805,7 +1808,7 @@ 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,
@@ -1815,7 +1818,7 @@ 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);
@@ -1831,7 +1834,7 @@ 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 (!slab_free_hook(s, object, slab_want_init_on_free(s))) {
+ if (slab_free_hook(s, object, slab_want_init_on_free(s))) {
/* Move object to the new freelist */
set_freepointer(s, object, *head);
*head = object;
@@ -1846,9 +1849,6 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
}
} while (object != old_tail);
- if (*head == *tail)
- *tail = NULL;
-
return *head != NULL;
}
@@ -3743,7 +3743,6 @@ 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;
@@ -3762,14 +3761,14 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
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);
@@ -3786,7 +3785,7 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
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);
@@ -3799,15 +3798,27 @@ 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);
/*
@@ -3821,13 +3832,13 @@ 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
void __kmem_cache_free(struct kmem_cache *s, void *x, unsigned long caller)
{
- slab_free(s, virt_to_slab(x), x, NULL, &x, 1, caller);
+ slab_free(s, virt_to_slab(x), x, caller);
}
void kmem_cache_free(struct kmem_cache *s, void *x)
@@ -3836,7 +3847,7 @@ 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);
@@ -3953,8 +3964,8 @@ 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);
--
2.43.0
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