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mm/slub: optimize free fast path code layout

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Inspection of kmem_cache_free() disassembly showed we could make the
fast path smaller by providing few more hints to the compiler, and
splitting the memcg_slab_free_hook() into an inline part that only
checks if there's work to do, and an out of line part doing the actual
uncharge.

bloat-o-meter results:
add/remove: 2/0 grow/shrink: 0/3 up/down: 286/-554 (-268)
Function                                     old     new   delta
__memcg_slab_free_hook                         -     270    +270
__pfx___memcg_slab_free_hook                   -      16     +16
kfree                                        828     665    -163
kmem_cache_free                             1116     948    -168
kmem_cache_free_bulk.part                   1701    1478    -223

Checking kmem_cache_free() disassembly now shows the non-fastpath
cases are handled out of line, which should reduce instruction cache
usage.

Acked-by: David Rientjes <rientjes@google.com>
Tested-by: David Rientjes <rientjes@google.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Vlastimil Babka 2023-10-27 12:34:18 +02:00
parent 3450a0e5a6
commit ecf9a253ce
1 changed files with 24 additions and 16 deletions
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40
mm/slub.c
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@ -1959,20 +1959,11 @@ void memcg_slab_post_alloc_hook(struct kmem_cache *s, struct obj_cgroup *objcg,
return __memcg_slab_post_alloc_hook(s, objcg, flags, size, p);
}
static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects)
static void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects,
struct obj_cgroup **objcgs)
{
struct obj_cgroup **objcgs;
int i;
if (!memcg_kmem_online())
return;
objcgs = slab_objcgs(slab);
if (!objcgs)
return;
for (i = 0; i < objects; i++) {
for (int i = 0; i < objects; i++) {
struct obj_cgroup *objcg;
unsigned int off;
@ -1988,6 +1979,22 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
obj_cgroup_put(objcg);
}
}
static __fastpath_inline
void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
int objects)
{
struct obj_cgroup **objcgs;
if (!memcg_kmem_online())
return;
objcgs = slab_objcgs(slab);
if (likely(!objcgs))
return;
__memcg_slab_free_hook(s, slab, p, objects, objcgs);
}
#else /* CONFIG_MEMCG_KMEM */
static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
{
@ -2047,7 +2054,7 @@ static __always_inline bool slab_free_hook(struct kmem_cache *s,
* The initialization memset's clear the object and the metadata,
* but don't touch the SLAB redzone.
*/
if (init) {
if (unlikely(init)) {
int rsize;
if (!kasan_has_integrated_init())
@ -2083,7 +2090,8 @@ 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 (!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;
@ -4282,7 +4290,7 @@ static __fastpath_inline void slab_free(struct kmem_cache *s, struct slab *slab,
* With KASAN enabled slab_free_freelist_hook modifies the freelist
* to remove objects, whose reuse must be delayed.
*/
if (slab_free_freelist_hook(s, &head, &tail, &cnt))
if (likely(slab_free_freelist_hook(s, &head, &tail, &cnt)))
do_slab_free(s, slab, head, tail, cnt, addr);
}