Commit f7ce3190 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
Browse files

slab: embed memcg_cache_params to kmem_cache 



Currently, kmem_cache stores a pointer to struct memcg_cache_params
instead of embedding it.  The rationale is to save memory when kmem
accounting is disabled.  However, the memcg_cache_params has shrivelled
drastically since it was first introduced:

* Initially:

struct memcg_cache_params {
	bool is_root_cache;
	union {
		struct kmem_cache *memcg_caches[0];
		struct {
			struct mem_cgroup *memcg;
			struct list_head list;
			struct kmem_cache *root_cache;
			bool dead;
			atomic_t nr_pages;
			struct work_struct destroy;
		};
	};
};

* Now:

struct memcg_cache_params {
	bool is_root_cache;
	union {
		struct {
			struct rcu_head rcu_head;
			struct kmem_cache *memcg_caches[0];
		};
		struct {
			struct mem_cgroup *memcg;
			struct kmem_cache *root_cache;
		};
	};
};

So the memory saving does not seem to be a clear win anymore.

OTOH, keeping a pointer to memcg_cache_params struct instead of embedding
it results in touching one more cache line on kmem alloc/free hot paths.
Besides, it makes linking kmem caches in a list chained by a field of
struct memcg_cache_params really painful due to a level of indirection,
while I want to make them linked in the following patch.  That said, let
us embed it.

Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
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: Dave Chinner <david@fromorbit.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 49e7e7ff

include/linux/slab.h

+7 −10
Original line number Diff line number Diff line
@@ -473,14 +473,14 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node) 
#ifndef ARCH_SLAB_MINALIGN

#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)

#endif



struct memcg_cache_array {

	struct rcu_head rcu;

	struct kmem_cache *entries[0];

};



/*

 * This is the main placeholder for memcg-related information in kmem caches.

 * struct kmem_cache will hold a pointer to it, so the memory cost while

 * disabled is 1 pointer. The runtime cost while enabled, gets bigger than it

 * would otherwise be if that would be bundled in kmem_cache: we'll need an

 * extra pointer chase. But the trade off clearly lays in favor of not

 * penalizing non-users.

 *

 * Both the root cache and the child caches will have it. For the root cache,

 * this will hold a dynamically allocated array large enough to hold

 * information about the currently limited memcgs in the system. To allow the
@@ -495,10 +495,7 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node) 
struct memcg_cache_params {

	bool is_root_cache;

	union {

		struct {

			struct rcu_head rcu_head;

			struct kmem_cache *memcg_caches[0];

		};

		struct memcg_cache_array __rcu *memcg_caches;

		struct {

			struct mem_cgroup *memcg;

			struct kmem_cache *root_cache;

include/linux/slab_def.h

+1 −1
Original line number Diff line number Diff line
@@ -70,7 +70,7 @@ struct kmem_cache { 
	int obj_offset;

#endif /* CONFIG_DEBUG_SLAB */

#ifdef CONFIG_MEMCG_KMEM

	struct memcg_cache_params *memcg_params;

	struct memcg_cache_params memcg_params;

#endif



	struct kmem_cache_node *node[MAX_NUMNODES];

include/linux/slub_def.h

+1 −1
Original line number Diff line number Diff line
@@ -85,7 +85,7 @@ struct kmem_cache { 
	struct kobject kobj;	/* For sysfs */

#endif

#ifdef CONFIG_MEMCG_KMEM

	struct memcg_cache_params *memcg_params;

	struct memcg_cache_params memcg_params;

	int max_attr_size; /* for propagation, maximum size of a stored attr */

#ifdef CONFIG_SYSFS

	struct kset *memcg_kset;

mm/memcontrol.c

+5 −6
Original line number Diff line number Diff line
@@ -332,7 +332,7 @@ struct mem_cgroup { 
	struct cg_proto tcp_mem;

#endif

#if defined(CONFIG_MEMCG_KMEM)

        /* Index in the kmem_cache->memcg_params->memcg_caches array */

        /* Index in the kmem_cache->memcg_params.memcg_caches array */

	int kmemcg_id;

#endif
@@ -531,7 +531,7 @@ static void disarm_sock_keys(struct mem_cgroup *memcg) 


#ifdef CONFIG_MEMCG_KMEM

/*

 * This will be the memcg's index in each cache's ->memcg_params->memcg_caches.

 * This will be the memcg's index in each cache's ->memcg_params.memcg_caches.

 * The main reason for not using cgroup id for this:

 *  this works better in sparse environments, where we have a lot of memcgs,

 *  but only a few kmem-limited. Or also, if we have, for instance, 200
@@ -2667,8 +2667,7 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep) 
	struct mem_cgroup *memcg;

	struct kmem_cache *memcg_cachep;



	VM_BUG_ON(!cachep->memcg_params);

	VM_BUG_ON(!cachep->memcg_params->is_root_cache);

	VM_BUG_ON(!is_root_cache(cachep));



	if (current->memcg_kmem_skip_account)

		return cachep;
@@ -2702,7 +2701,7 @@ out: 
void __memcg_kmem_put_cache(struct kmem_cache *cachep)

{

	if (!is_root_cache(cachep))

		css_put(&cachep->memcg_params->memcg->css);

		css_put(&cachep->memcg_params.memcg->css);

}



/*
@@ -2778,7 +2777,7 @@ struct mem_cgroup *__mem_cgroup_from_kmem(void *ptr) 
	if (PageSlab(page)) {

		cachep = page->slab_cache;

		if (!is_root_cache(cachep))

			memcg = cachep->memcg_params->memcg;

			memcg = cachep->memcg_params.memcg;

	} else

		/* page allocated by alloc_kmem_pages */

		memcg = page->mem_cgroup;

mm/slab.h

+23 −25
Original line number Diff line number Diff line
@@ -86,8 +86,6 @@ extern struct kmem_cache *create_kmalloc_cache(const char *name, size_t size, 
extern void create_boot_cache(struct kmem_cache *, const char *name,

			size_t size, unsigned long flags);



struct mem_cgroup;



int slab_unmergeable(struct kmem_cache *s);

struct kmem_cache *find_mergeable(size_t size, size_t align,

		unsigned long flags, const char *name, void (*ctor)(void *));
@@ -167,14 +165,13 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer, 
#ifdef CONFIG_MEMCG_KMEM

static inline bool is_root_cache(struct kmem_cache *s)

{

	return !s->memcg_params || s->memcg_params->is_root_cache;

	return s->memcg_params.is_root_cache;

}



static inline bool slab_equal_or_root(struct kmem_cache *s,

				      struct kmem_cache *p)

{

	return (p == s) ||

		(s->memcg_params && (p == s->memcg_params->root_cache));

	return p == s || p == s->memcg_params.root_cache;

}



/*
@@ -185,37 +182,30 @@ static inline bool slab_equal_or_root(struct kmem_cache *s, 
static inline const char *cache_name(struct kmem_cache *s)

{

	if (!is_root_cache(s))

		return s->memcg_params->root_cache->name;

		s = s->memcg_params.root_cache;

	return s->name;

}



/*

 * Note, we protect with RCU only the memcg_caches array, not per-memcg caches.

 * That said the caller must assure the memcg's cache won't go away. Since once

 * created a memcg's cache is destroyed only along with the root cache, it is

 * true if we are going to allocate from the cache or hold a reference to the

 * root cache by other means. Otherwise, we should hold either the slab_mutex

 * or the memcg's slab_caches_mutex while calling this function and accessing

 * the returned value.

 * That said the caller must assure the memcg's cache won't go away by either

 * taking a css reference to the owner cgroup, or holding the slab_mutex.

 */

static inline struct kmem_cache *

cache_from_memcg_idx(struct kmem_cache *s, int idx)

{

	struct kmem_cache *cachep;

	struct memcg_cache_params *params;



	if (!s->memcg_params)

		return NULL;

	struct memcg_cache_array *arr;



	rcu_read_lock();

	params = rcu_dereference(s->memcg_params);

	arr = rcu_dereference(s->memcg_params.memcg_caches);



	/*

	 * Make sure we will access the up-to-date value. The code updating

	 * memcg_caches issues a write barrier to match this (see

	 * memcg_register_cache()).

	 * memcg_create_kmem_cache()).

	 */

	cachep = lockless_dereference(params->memcg_caches[idx]);

	cachep = lockless_dereference(arr->entries[idx]);

	rcu_read_unlock();



	return cachep;
@@ -225,7 +215,7 @@ static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s) 
{

	if (is_root_cache(s))

		return s;

	return s->memcg_params->root_cache;

	return s->memcg_params.root_cache;

}



static __always_inline int memcg_charge_slab(struct kmem_cache *s,
@@ -235,7 +225,7 @@ static __always_inline int memcg_charge_slab(struct kmem_cache *s, 
		return 0;

	if (is_root_cache(s))

		return 0;

	return memcg_charge_kmem(s->memcg_params->memcg, gfp, 1 << order);

	return memcg_charge_kmem(s->memcg_params.memcg, gfp, 1 << order);

}



static __always_inline void memcg_uncharge_slab(struct kmem_cache *s, int order)
@@ -244,9 +234,13 @@ static __always_inline void memcg_uncharge_slab(struct kmem_cache *s, int order) 
		return;

	if (is_root_cache(s))

		return;

	memcg_uncharge_kmem(s->memcg_params->memcg, 1 << order);

	memcg_uncharge_kmem(s->memcg_params.memcg, 1 << order);

}

#else



extern void slab_init_memcg_params(struct kmem_cache *);



#else /* !CONFIG_MEMCG_KMEM */



static inline bool is_root_cache(struct kmem_cache *s)

{

	return true;
@@ -282,7 +276,11 @@ static inline int memcg_charge_slab(struct kmem_cache *s, gfp_t gfp, int order) 
static inline void memcg_uncharge_slab(struct kmem_cache *s, int order)

{

}

#endif



static inline void slab_init_memcg_params(struct kmem_cache *s)

{

}

#endif /* CONFIG_MEMCG_KMEM */



static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)

{

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