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mm: memcg/slab: use a single set of kmem_caches for all accounted all…
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…ocations

This is fairly big but mostly red patch, which makes all accounted slab
allocations use a single set of kmem_caches instead of creating a separate
set for each memory cgroup.

Because the number of non-root kmem_caches is now capped by the number of
root kmem_caches, there is no need to shrink or destroy them prematurely.
They can be perfectly destroyed together with their root counterparts.
This allows to dramatically simplify the management of non-root
kmem_caches and delete a ton of code.

This patch performs the following changes:
1) introduces memcg_params.memcg_cache pointer to represent the
   kmem_cache which will be used for all non-root allocations
2) reuses the existing memcg kmem_cache creation mechanism
   to create memcg kmem_cache on the first allocation attempt
3) memcg kmem_caches are named <kmemcache_name>-memcg,
   e.g. dentry-memcg
4) simplifies memcg_kmem_get_cache() to just return memcg kmem_cache
   or schedule it's creation and return the root cache
5) removes almost all non-root kmem_cache management code
   (separate refcounter, reparenting, shrinking, etc)
6) makes slab debugfs to display root_mem_cgroup css id and never
   show :dead and :deact flags in the memcg_slabinfo attribute.

Following patches in the series will simplify the kmem_cache creation.

Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/20200623174037.3951353-13-guro@fb.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@rgushchin @torvalds
rgushchin authored and torvalds committed Aug 7, 2020
1 parent 0f876e4 commit 9855609
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Showing 7 changed files with 134 additions and 698 deletions.
5 changes: 1 addition & 4 deletions include/linux/memcontrol.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -317,7 +317,6 @@ struct mem_cgroup {
/* Index in the kmem_cache->memcg_params.memcg_caches array */
int kmemcg_id;
enum memcg_kmem_state kmem_state;
struct list_head kmem_caches;
struct obj_cgroup __rcu *objcg;
struct list_head objcg_list; /* list of inherited objcgs */
#endif
Expand Down Expand Up @@ -1404,9 +1403,7 @@ static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
}
#endif

struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep,
struct obj_cgroup **objcgp);
void memcg_kmem_put_cache(struct kmem_cache *cachep);
struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep);

#ifdef CONFIG_MEMCG_KMEM
int __memcg_kmem_charge(struct mem_cgroup *memcg, gfp_t gfp,
Expand Down
5 changes: 1 addition & 4 deletions include/linux/slab.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -155,8 +155,7 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name,
void kmem_cache_destroy(struct kmem_cache *);
int kmem_cache_shrink(struct kmem_cache *);

void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
void memcg_deactivate_kmem_caches(struct mem_cgroup *, struct mem_cgroup *);
void memcg_create_kmem_cache(struct kmem_cache *cachep);

/*
* Please use this macro to create slab caches. Simply specify the
Expand Down Expand Up @@ -580,8 +579,6 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
return __kmalloc_node(size, flags, node);
}

int memcg_update_all_caches(int num_memcgs);

/**
* kmalloc_array - allocate memory for an array.
* @n: number of elements.
Expand Down
163 changes: 32 additions & 131 deletions mm/memcontrol.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -350,7 +350,7 @@ static void memcg_reparent_objcgs(struct mem_cgroup *memcg,
}

/*
* This will be the memcg's index in each cache's ->memcg_params.memcg_caches.
* This will be used as a shrinker list's index.
* 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
Expand Down Expand Up @@ -569,20 +569,16 @@ ino_t page_cgroup_ino(struct page *page)
unsigned long ino = 0;

rcu_read_lock();
if (PageSlab(page) && !PageTail(page)) {
memcg = memcg_from_slab_page(page);
} else {
memcg = page->mem_cgroup;
memcg = page->mem_cgroup;

/*
* The lowest bit set means that memcg isn't a valid
* memcg pointer, but a obj_cgroups pointer.
* In this case the page is shared and doesn't belong
* to any specific memory cgroup.
*/
if ((unsigned long) memcg & 0x1UL)
memcg = NULL;
}
/*
* The lowest bit set means that memcg isn't a valid
* memcg pointer, but a obj_cgroups pointer.
* In this case the page is shared and doesn't belong
* to any specific memory cgroup.
*/
if ((unsigned long) memcg & 0x1UL)
memcg = NULL;

while (memcg && !(memcg->css.flags & CSS_ONLINE))
memcg = parent_mem_cgroup(memcg);
Expand Down Expand Up @@ -2822,12 +2818,18 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
page = virt_to_head_page(p);

/*
* Slab pages don't have page->mem_cgroup set because corresponding
* kmem caches can be reparented during the lifetime. That's why
* memcg_from_slab_page() should be used instead.
* Slab objects are accounted individually, not per-page.
* Memcg membership data for each individual object is saved in
* the page->obj_cgroups.
*/
if (PageSlab(page))
return memcg_from_slab_page(page);
if (page_has_obj_cgroups(page)) {
struct obj_cgroup *objcg;
unsigned int off;

off = obj_to_index(page->slab_cache, page, p);
objcg = page_obj_cgroups(page)[off];
return obj_cgroup_memcg(objcg);
}

/* All other pages use page->mem_cgroup */
return page->mem_cgroup;
Expand Down Expand Up @@ -2882,9 +2884,7 @@ static int memcg_alloc_cache_id(void)
else if (size > MEMCG_CACHES_MAX_SIZE)
size = MEMCG_CACHES_MAX_SIZE;

err = memcg_update_all_caches(size);
if (!err)
err = memcg_update_all_list_lrus(size);
err = memcg_update_all_list_lrus(size);
if (!err)
memcg_nr_cache_ids = size;

Expand All @@ -2903,7 +2903,6 @@ static void memcg_free_cache_id(int id)
}

struct memcg_kmem_cache_create_work {
struct mem_cgroup *memcg;
struct kmem_cache *cachep;
struct work_struct work;
};
Expand All @@ -2912,136 +2911,51 @@ static void memcg_kmem_cache_create_func(struct work_struct *w)
{
struct memcg_kmem_cache_create_work *cw =
container_of(w, struct memcg_kmem_cache_create_work, work);
struct mem_cgroup *memcg = cw->memcg;
struct kmem_cache *cachep = cw->cachep;

memcg_create_kmem_cache(memcg, cachep);
memcg_create_kmem_cache(cachep);

css_put(&memcg->css);
kfree(cw);
}

/*
* Enqueue the creation of a per-memcg kmem_cache.
*/
static void memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,
struct kmem_cache *cachep)
static void memcg_schedule_kmem_cache_create(struct kmem_cache *cachep)
{
struct memcg_kmem_cache_create_work *cw;

if (!css_tryget_online(&memcg->css))
return;

cw = kmalloc(sizeof(*cw), GFP_NOWAIT | __GFP_NOWARN);
if (!cw) {
css_put(&memcg->css);
if (!cw)
return;
}

cw->memcg = memcg;
cw->cachep = cachep;
INIT_WORK(&cw->work, memcg_kmem_cache_create_func);

queue_work(memcg_kmem_cache_wq, &cw->work);
}

/**
* memcg_kmem_get_cache: select the correct per-memcg cache for allocation
* memcg_kmem_get_cache: select memcg or root cache for allocation
* @cachep: the original global kmem cache
*
* Return the kmem_cache we're supposed to use for a slab allocation.
* We try to use the current memcg's version of the cache.
*
* If the cache does not exist yet, if we are the first user of it, we
* create it asynchronously in a workqueue and let the current allocation
* go through with the original cache.
*
* This function takes a reference to the cache it returns to assure it
* won't get destroyed while we are working with it. Once the caller is
* done with it, memcg_kmem_put_cache() must be called to release the
* reference.
*/
struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep,
struct obj_cgroup **objcgp)
struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
{
struct mem_cgroup *memcg;
struct kmem_cache *memcg_cachep;
struct memcg_cache_array *arr;
int kmemcg_id;

VM_BUG_ON(!is_root_cache(cachep));

if (memcg_kmem_bypass())
memcg_cachep = READ_ONCE(cachep->memcg_params.memcg_cache);
if (unlikely(!memcg_cachep)) {
memcg_schedule_kmem_cache_create(cachep);
return cachep;

rcu_read_lock();

if (unlikely(current->active_memcg))
memcg = current->active_memcg;
else
memcg = mem_cgroup_from_task(current);

if (!memcg || memcg == root_mem_cgroup)
goto out_unlock;

kmemcg_id = READ_ONCE(memcg->kmemcg_id);
if (kmemcg_id < 0)
goto out_unlock;

arr = rcu_dereference(cachep->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 the data dependency
* barrier inside READ_ONCE() (see memcg_create_kmem_cache()).
*/
memcg_cachep = READ_ONCE(arr->entries[kmemcg_id]);

/*
* If we are in a safe context (can wait, and not in interrupt
* context), we could be be predictable and return right away.
* This would guarantee that the allocation being performed
* already belongs in the new cache.
*
* However, there are some clashes that can arrive from locking.
* For instance, because we acquire the slab_mutex while doing
* memcg_create_kmem_cache, this means no further allocation
* could happen with the slab_mutex held. So it's better to
* defer everything.
*
* If the memcg is dying or memcg_cache is about to be released,
* don't bother creating new kmem_caches. Because memcg_cachep
* is ZEROed as the fist step of kmem offlining, we don't need
* percpu_ref_tryget_live() here. css_tryget_online() check in
* memcg_schedule_kmem_cache_create() will prevent us from
* creation of a new kmem_cache.
*/
if (unlikely(!memcg_cachep))
memcg_schedule_kmem_cache_create(memcg, cachep);
else if (percpu_ref_tryget(&memcg_cachep->memcg_params.refcnt)) {
struct obj_cgroup *objcg = rcu_dereference(memcg->objcg);

if (!objcg || !obj_cgroup_tryget(objcg)) {
percpu_ref_put(&memcg_cachep->memcg_params.refcnt);
goto out_unlock;
}

*objcgp = objcg;
cachep = memcg_cachep;
}
out_unlock:
rcu_read_unlock();
return cachep;
}

/**
* memcg_kmem_put_cache: drop reference taken by memcg_kmem_get_cache
* @cachep: the cache returned by memcg_kmem_get_cache
*/
void memcg_kmem_put_cache(struct kmem_cache *cachep)
{
if (!is_root_cache(cachep))
percpu_ref_put(&cachep->memcg_params.refcnt);
return memcg_cachep;
}

/**
Expand Down Expand Up @@ -3731,7 +3645,6 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
*/
memcg->kmemcg_id = memcg_id;
memcg->kmem_state = KMEM_ONLINE;
INIT_LIST_HEAD(&memcg->kmem_caches);

return 0;
}
Expand All @@ -3744,22 +3657,13 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)

if (memcg->kmem_state != KMEM_ONLINE)
return;
/*
* Clear the online state before clearing memcg_caches array
* entries. The slab_mutex in memcg_deactivate_kmem_caches()
* guarantees that no cache will be created for this cgroup
* after we are done (see memcg_create_kmem_cache()).
*/

memcg->kmem_state = KMEM_ALLOCATED;

parent = parent_mem_cgroup(memcg);
if (!parent)
parent = root_mem_cgroup;

/*
* Deactivate and reparent kmem_caches and objcgs.
*/
memcg_deactivate_kmem_caches(memcg, parent);
memcg_reparent_objcgs(memcg, parent);

kmemcg_id = memcg->kmemcg_id;
Expand Down Expand Up @@ -5384,9 +5288,6 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)

/* The following stuff does not apply to the root */
if (!parent) {
#ifdef CONFIG_MEMCG_KMEM
INIT_LIST_HEAD(&memcg->kmem_caches);
#endif
root_mem_cgroup = memcg;
return &memcg->css;
}
Expand Down
16 changes: 3 additions & 13 deletions mm/slab.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1249,7 +1249,7 @@ void __init kmem_cache_init(void)
nr_node_ids * sizeof(struct kmem_cache_node *),
SLAB_HWCACHE_ALIGN, 0, 0);
list_add(&kmem_cache->list, &slab_caches);
memcg_link_cache(kmem_cache, NULL);
memcg_link_cache(kmem_cache);
slab_state = PARTIAL;

/*
Expand Down Expand Up @@ -2253,17 +2253,6 @@ int __kmem_cache_shrink(struct kmem_cache *cachep)
return (ret ? 1 : 0);
}

#ifdef CONFIG_MEMCG
void __kmemcg_cache_deactivate(struct kmem_cache *cachep)
{
__kmem_cache_shrink(cachep);
}

void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
{
}
#endif

int __kmem_cache_shutdown(struct kmem_cache *cachep)
{
return __kmem_cache_shrink(cachep);
Expand Down Expand Up @@ -3872,7 +3861,8 @@ static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
return ret;

lockdep_assert_held(&slab_mutex);
for_each_memcg_cache(c, cachep) {
c = memcg_cache(cachep);
if (c) {
/* return value determined by the root cache only */
__do_tune_cpucache(c, limit, batchcount, shared, gfp);
}
Expand Down
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