Commit 4138fdfc authored by Roman Gushchin's avatar Roman Gushchin Committed by Linus Torvalds
Browse files

mm: slub: implement SLUB version of obj_to_index() 



This commit implements SLUB version of the obj_to_index() function, which
will be required to calculate the offset of obj_cgroup in the obj_cgroups
vector to store/obtain the objcg ownership data.

To make it faster, let's repeat the SLAB's trick introduced by commit
6a2d7a95 ("SLAB: use a multiply instead of a divide in
obj_to_index()") and avoid an expensive division.

Vlastimil Babka noticed, that SLUB does have already a similar function
called slab_index(), which is defined only if SLUB_DEBUG is enabled.  The
function does a similar math, but with a division, and it also takes a
page address instead of a page pointer.

Let's remove slab_index() and replace it with the new helper
__obj_to_index(), which takes a page address.  obj_to_index() will be a
simple wrapper taking a page pointer and passing page_address(page) into
__obj_to_index().

Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/20200623174037.3951353-5-guro@fb.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d42f3245

include/linux/slub_def.h

+16 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
 * (C) 2007 SGI, Christoph Lameter

 */

#include <linux/kobject.h>

#include <linux/reciprocal_div.h>



enum stat_item {

	ALLOC_FASTPATH,		/* Allocation from cpu slab */
@@ -86,6 +87,7 @@ struct kmem_cache { 
	unsigned long min_partial;

	unsigned int size;	/* The size of an object including metadata */

	unsigned int object_size;/* The size of an object without metadata */

	struct reciprocal_value reciprocal_size;

	unsigned int offset;	/* Free pointer offset */

#ifdef CONFIG_SLUB_CPU_PARTIAL

	/* Number of per cpu partial objects to keep around */
@@ -182,4 +184,18 @@ static inline void *nearest_obj(struct kmem_cache *cache, struct page *page, 
	return result;

}



/* Determine object index from a given position */

static inline unsigned int __obj_to_index(const struct kmem_cache *cache,

					  void *addr, void *obj)

{

	return reciprocal_divide(kasan_reset_tag(obj) - addr,

				 cache->reciprocal_size);

}



static inline unsigned int obj_to_index(const struct kmem_cache *cache,

					const struct page *page, void *obj)

{

	return __obj_to_index(cache, page_address(page), obj);

}



#endif /* _LINUX_SLUB_DEF_H */

mm/slub.c

+5 −10
Original line number Diff line number Diff line
@@ -317,12 +317,6 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) 
		__p < (__addr) + (__objects) * (__s)->size; \

		__p += (__s)->size)



/* Determine object index from a given position */

static inline unsigned int slab_index(void *p, struct kmem_cache *s, void *addr)

{

	return (kasan_reset_tag(p) - addr) / s->size;

}



static inline unsigned int order_objects(unsigned int order, unsigned int size)

{

	return ((unsigned int)PAGE_SIZE << order) / size;
@@ -465,7 +459,7 @@ static unsigned long *get_map(struct kmem_cache *s, struct page *page) 
	bitmap_zero(object_map, page->objects);



	for (p = page->freelist; p; p = get_freepointer(s, p))

		set_bit(slab_index(p, s, addr), object_map);

		set_bit(__obj_to_index(s, addr, p), object_map);



	return object_map;

}
@@ -3754,6 +3748,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) 
	 */

	size = ALIGN(size, s->align);

	s->size = size;

	s->reciprocal_size = reciprocal_value(size);

	if (forced_order >= 0)

		order = forced_order;

	else
@@ -3858,7 +3853,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page, 
	map = get_map(s, page);

	for_each_object(p, s, addr, page->objects) {



		if (!test_bit(slab_index(p, s, addr), map)) {

		if (!test_bit(__obj_to_index(s, addr, p), map)) {

			pr_err("INFO: Object 0x%p @offset=%tu\n", p, p - addr);

			print_tracking(s, p);

		}
@@ -4574,7 +4569,7 @@ static void validate_slab(struct kmem_cache *s, struct page *page) 
	/* Now we know that a valid freelist exists */

	map = get_map(s, page);

	for_each_object(p, s, addr, page->objects) {

		u8 val = test_bit(slab_index(p, s, addr), map) ?

		u8 val = test_bit(__obj_to_index(s, addr, p), map) ?

			 SLUB_RED_INACTIVE : SLUB_RED_ACTIVE;



		if (!check_object(s, page, p, val))
@@ -4765,7 +4760,7 @@ static void process_slab(struct loc_track *t, struct kmem_cache *s, 


	map = get_map(s, page);

	for_each_object(p, s, addr, page->objects)

		if (!test_bit(slab_index(p, s, addr), map))

		if (!test_bit(__obj_to_index(s, addr, p), map))

			add_location(t, s, get_track(s, p, alloc));

	put_map(map);

}

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