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Commit 376bf125 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Linus Torvalds
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slub: clean up code for kmem cgroup support to kmem_cache_free_bulk 



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
03374518 ("slub: add missing kmem cgroup support to
kmem_cache_free_bulk").

Fixes: 03374518 ("slub: add missing kmem cgroup support to kmem_cache_free_bulk")
Signed-off-by: default avatarJesper 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent dec63a4d

mm/slub.c

+11 −11
Original line number Diff line number Diff line
@@ -2815,6 +2815,7 @@ struct detached_freelist { 
	void *tail;

	void *freelist;

	int cnt;

	struct kmem_cache *s;

};



/*
@@ -2829,7 +2830,8 @@ 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,

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;
@@ -2846,8 +2848,11 @@ static int build_detached_freelist(struct kmem_cache *s, size_t size, 
	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;
@@ -2862,7 +2867,7 @@ static int build_detached_freelist(struct kmem_cache *s, size_t size, 
		/* 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 */
@@ -2881,25 +2886,20 @@ static int build_detached_freelist(struct kmem_cache *s, size_t size, 
	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);