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mm: slab: optimize memcg_slab_free_hook()

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Most callers of memcg_slab_free_hook() already know the slab,  which could
be passed to memcg_slab_free_hook() directly to reduce the overhead of an
another call of virt_to_slab().  For bulk freeing of objects, the call of
slab_objcgs() in the loop in memcg_slab_free_hook() is redundant as well.
Rework memcg_slab_free_hook() and build_detached_freelist() to reduce
those unnecessary overhead and make memcg_slab_free_hook() can handle bulk
freeing in slab_free().

Move the calling site of memcg_slab_free_hook() from do_slab_free() to
slab_free() for slub to make the code clearer since the logic is weird
(e.g. the caller need to judge whether it needs to call
memcg_slab_free_hook()). It is easy to make mistakes like missing calling
of memcg_slab_free_hook() like fixes of:

  commit d1b2cf6cb8 ("mm: memcg/slab: uncharge during kmem_cache_free_bulk()")
  commit ae085d7f93 ("mm: kfence: fix missing objcg housekeeping for SLAB")

This optimization is mainly for bulk objects freeing.  The following numbers
is shown for 16-object freeing.

                           before      after
  kmem_cache_free_bulk:   ~430 ns     ~400 ns

The overhead is reduced by about 7% for 16-object freeing.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Link: https://lore.kernel.org/r/20220429123044.37885-1-songmuchun@bytedance.com
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Muchun Song 2022-04-29 20:30:44 +08:00 committed by Vlastimil Babka
parent b347aa7b57
commit b77d5b1b83
3 changed files with 32 additions and 68 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
mm/slab.c
View File

@ -3406,9 +3406,10 @@ static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp,
{
bool init;
memcg_slab_free_hook(cachep, virt_to_slab(objp), &objp, 1);
if (is_kfence_address(objp)) {
kmemleak_free_recursive(objp, cachep->flags);
memcg_slab_free_hook(cachep, &objp, 1);
__kfence_free(objp);
return;
}
@ -3441,7 +3442,6 @@ void ___cache_free(struct kmem_cache *cachep, void *objp,
check_irq_off();
kmemleak_free_recursive(objp, cachep->flags);
objp = cache_free_debugcheck(cachep, objp, caller);
memcg_slab_free_hook(cachep, &objp, 1);
/*
* Skip calling cache_free_alien() when the platform is not numa.

30
mm/slab.h
View File

@ -547,36 +547,22 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
obj_cgroup_put(objcg);
}
static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects)
{
struct kmem_cache *s;
struct obj_cgroup **objcgs;
struct obj_cgroup *objcg;
struct slab *slab;
unsigned int off;
int i;
if (!memcg_kmem_enabled())
return;
objcgs = slab_objcgs(slab);
if (!objcgs)
return;
for (i = 0; i < objects; i++) {
if (unlikely(!p[i]))
continue;
slab = virt_to_slab(p[i]);
/* we could be given a kmalloc_large() object, skip those */
if (!slab)
continue;
objcgs = slab_objcgs(slab);
if (!objcgs)
continue;
if (!s_orig)
s = slab->slab_cache;
else
s = s_orig;
struct obj_cgroup *objcg;
unsigned int off;
off = obj_to_index(s, slab, p[i]);
objcg = objcgs[off];
@ -628,7 +614,7 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
{
}
static inline void memcg_slab_free_hook(struct kmem_cache *s,
static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects)
{
}

66
mm/slub.c
View File

@ -3464,9 +3464,6 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
struct kmem_cache_cpu *c;
unsigned long tid;
/* memcg_slab_free_hook() is already called for bulk free. */
if (!tail)
memcg_slab_free_hook(s, &head, 1);
redo:
/*
* Determine the currently cpus per cpu slab.
@ -3526,9 +3523,10 @@ redo:
}
static __always_inline void slab_free(struct kmem_cache *s, struct slab *slab,
void *head, void *tail, int cnt,
void *head, void *tail, void **p, int cnt,
unsigned long addr)
{
memcg_slab_free_hook(s, slab, p, cnt);
/*
* With KASAN enabled slab_free_freelist_hook modifies the freelist
* to remove objects, whose reuse must be delayed.
@ -3550,7 +3548,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
if (!s)
return;
trace_kmem_cache_free(_RET_IP_, x, s->name);
slab_free(s, virt_to_slab(x), x, NULL, 1, _RET_IP_);
slab_free(s, virt_to_slab(x), x, NULL, &x, 1, _RET_IP_);
}
EXPORT_SYMBOL(kmem_cache_free);
@ -3591,79 +3589,59 @@ static inline
int build_detached_freelist(struct kmem_cache *s, size_t size,
void **p, struct detached_freelist *df)
{
size_t first_skipped_index = 0;
int lookahead = 3;
void *object;
struct folio *folio;
struct slab *slab;
/* Always re-init detached_freelist */
df->slab = NULL;
do {
object = p[--size];
/* Do we need !ZERO_OR_NULL_PTR(object) here? (for kfree) */
} while (!object && size);
if (!object)
return 0;
size_t same;
object = p[--size];
folio = virt_to_folio(object);
if (!s) {
/* Handle kalloc'ed objects */
if (unlikely(!folio_test_slab(folio))) {
free_large_kmalloc(folio, object);
p[size] = NULL; /* mark object processed */
df->slab = NULL;
return size;
}
/* Derive kmem_cache from object */
slab = folio_slab(folio);
df->s = slab->slab_cache;
df->slab = folio_slab(folio);
df->s = df->slab->slab_cache;
} else {
slab = folio_slab(folio);
df->slab = folio_slab(folio);
df->s = cache_from_obj(s, object); /* Support for memcg */
}
if (is_kfence_address(object)) {
slab_free_hook(df->s, object, false);
__kfence_free(object);
p[size] = NULL; /* mark object processed */
return size;
}
/* Start new detached freelist */
df->slab = slab;
set_freepointer(df->s, object, NULL);
df->tail = object;
df->freelist = object;
p[size] = NULL; /* mark object processed */
df->cnt = 1;
if (is_kfence_address(object))
return size;
set_freepointer(df->s, object, NULL);
same = size;
while (size) {
object = p[--size];
if (!object)
continue; /* Skip processed objects */
/* df->slab is always set at this point */
if (df->slab == virt_to_slab(object)) {
/* Opportunity build freelist */
set_freepointer(df->s, object, df->freelist);
df->freelist = object;
df->cnt++;
p[size] = NULL; /* mark object processed */
same--;
if (size != same)
swap(p[size], p[same]);
continue;
}
/* Limit look ahead search */
if (!--lookahead)
break;
if (!first_skipped_index)
first_skipped_index = size + 1;
}
return first_skipped_index;
return same;
}
/* Note that interrupts must be enabled when calling this function. */
@ -3672,7 +3650,6 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
if (WARN_ON(!size))
return;
memcg_slab_free_hook(s, p, size);
do {
struct detached_freelist df;
@ -3680,7 +3657,8 @@ 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, df.cnt, _RET_IP_);
slab_free(df.s, df.slab, df.freelist, df.tail, &p[size], df.cnt,
_RET_IP_);
} while (likely(size));
}
EXPORT_SYMBOL(kmem_cache_free_bulk);
@ -4581,7 +4559,7 @@ void kfree(const void *x)
return;
}
slab = folio_slab(folio);
slab_free(slab->slab_cache, slab, object, NULL, 1, _RET_IP_);
slab_free(slab->slab_cache, slab, object, NULL, &object, 1, _RET_IP_);
}
EXPORT_SYMBOL(kfree);