[PATCH 4.4 101/163] slub: clean up code for kmem cgroup support to kmem_cache_free_bulk

Greg Kroah-Hartman
2016-05-03T00:23:29Z

From: Jesper Dangaard Brouer <brouer@redhat.com>

commit 376bf125ac781d32e202760ed7deb1ae4ed35d31 upstream.

This change is primarily an attempt to make it easier to realize the
optimizations the compiler performs in-case CONFIG_MEMCG_KMEM is not
enabled.

Performance wise, even when CONFIG_MEMCG_KMEM is compiled in, the
overhead is zero. This is because, as long as no process have enabled
kmem cgroups accounting, the assignment is replaced by asm-NOP
operations. This is possible because memcg_kmem_enabled() uses a
static_key_false() construct.

It also helps readability as it avoid accessing the p[] array like:
p[size - 1] which "expose" that the array is processed backwards inside
helper function build_detached_freelist().

Lastly this also makes the code more robust, in error case like passing
NULL pointers in the array. Which were previously handled before commit
033745189b1b ("slub: add missing kmem cgroup support to
kmem_cache_free_bulk").

Fixes: 033745189b1b ("slub: add missing kmem cgroup support to kmem_cache_free_bulk")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/slub.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2819,6 +2819,7 @@ struct detached_freelist {
void *tail;
void *freelist;
int cnt;
+ struct kmem_cache *s;
};

/*
@@ -2833,8 +2834,9 @@ struct detached_freelist {
* synchronization primitive. Look ahead in the array is limited due
* to performance reasons.
*/
-static int build_detached_freelist(struct kmem_cache *s, size_t size,
- void **p, struct detached_freelist *df)
+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;
@@ -2850,8 +2852,11 @@ static int build_detached_freelist(struc
if (!object)
return 0;

+ /* Support for memcg, compiler can optimize this out */
+ df->s = cache_from_obj(s, object);
+
/* Start new detached freelist */
- set_freepointer(s, object, NULL);
+ set_freepointer(df->s, object, NULL);
df->page = virt_to_head_page(object);
df->tail = object;
df->freelist = object;
@@ -2866,7 +2871,7 @@ static int build_detached_freelist(struc
/* df->page is always set at this point */
if (df->page == virt_to_head_page(object)) {
/* Opportunity build freelist */
- set_freepointer(s, object, df->freelist);
+ set_freepointer(df->s, object, df->freelist);
df->freelist = object;
df->cnt++;
p[size] = NULL; /* mark object processed */
@@ -2885,25 +2890,20 @@ static int build_detached_freelist(struc
return first_skipped_index;
}

-
/* Note that interrupts must be enabled when calling this function. */
-void kmem_cache_free_bulk(struct kmem_cache *orig_s, size_t size, void **p)
+void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
{
if (WARN_ON(!size))
return;

do {
struct detached_freelist df;
- struct kmem_cache *s;
-
- /* Support for memcg */
- s = cache_from_obj(orig_s, p[size - 1]);

size = build_detached_freelist(s, size, p, &df);
if (unlikely(!df.page))
continue;

- slab_free(s, df.page, df.freelist, df.tail, df.cnt, _RET_IP_);
+ slab_free(df.s, df.page, df.freelist, df.tail, df.cnt,_RET_IP_);
} while (likely(size));
}
EXPORT_SYMBOL(kmem_cache_free_bulk);