[RFC PATCH 11/30] mm: introduce slabobj_ext to support slab object extensions

Suren Baghdasaryan
2022-08-30T21:51:40Z

Currently slab pages can store only vectors of obj_cgroup pointers in
page->memcg_data. Introduce slabobj_ext structure to allow more data
to be stored for each slab object. Wraps obj_cgroup into slabobj_ext
to support current functionality while allowing to extend slabobj_ext
in the future.

Note: ideally the config dependency should be turned the other way around:
MEMCG should depend on SLAB_OBJ_EXT and {page|slab|folio}.memcg_data would
be renamed to something like {page|slab|folio}.objext_data. However doing
this in RFC would introduce considerable churn unrelated to the overall
idea, so avoiding this until v1.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/memcontrol.h | 18 ++++--
init/Kconfig | 5 ++
mm/kfence/core.c | 2 +-
mm/memcontrol.c | 60 ++++++++++---------
mm/page_owner.c | 2 +-
mm/slab.h | 119 +++++++++++++++++++++++++------------
6 files changed, 131 insertions(+), 75 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6257867fbf95..315399f77173 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -227,6 +227,14 @@ struct obj_cgroup {
};
};

+/*
+ * Extended information for slab objects stored as an array in page->memcg_data
+ * if MEMCG_DATA_OBJEXTS is set.
+ */
+struct slabobj_ext {
+ struct obj_cgroup *objcg;
+} __aligned(8);
+
/*
* The memory controller data structure. The memory controller controls both
* page cache and RSS per cgroup. We would eventually like to provide
@@ -363,7 +371,7 @@ extern struct mem_cgroup *root_mem_cgroup;

enum page_memcg_data_flags {
/* page->memcg_data is a pointer to an objcgs vector */
- MEMCG_DATA_OBJCGS = (1UL << 0),
+ MEMCG_DATA_OBJEXTS = (1UL << 0),
/* page has been accounted as a non-slab kernel page */
MEMCG_DATA_KMEM = (1UL << 1),
/* the next bit after the last actual flag */
@@ -401,7 +409,7 @@ static inline struct mem_cgroup *__folio_memcg(struct folio *folio)
unsigned long memcg_data = folio->memcg_data;

VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
- VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJCGS, folio);
+ VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJEXTS, folio);
VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_KMEM, folio);

return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
@@ -422,7 +430,7 @@ static inline struct obj_cgroup *__folio_objcg(struct folio *folio)
unsigned long memcg_data = folio->memcg_data;

VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
- VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJCGS, folio);
+ VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJEXTS, folio);
VM_BUG_ON_FOLIO(!(memcg_data & MEMCG_DATA_KMEM), folio);

return (struct obj_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
@@ -517,7 +525,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page)
*/
unsigned long memcg_data = READ_ONCE(page->memcg_data);

- if (memcg_data & MEMCG_DATA_OBJCGS)
+ if (memcg_data & MEMCG_DATA_OBJEXTS)
return NULL;

if (memcg_data & MEMCG_DATA_KMEM) {
@@ -556,7 +564,7 @@ static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *ob
static inline bool folio_memcg_kmem(struct folio *folio)
{
VM_BUG_ON_PGFLAGS(PageTail(&folio->page), &folio->page);
- VM_BUG_ON_FOLIO(folio->memcg_data & MEMCG_DATA_OBJCGS, folio);
+ VM_BUG_ON_FOLIO(folio->memcg_data & MEMCG_DATA_OBJEXTS, folio);
return folio->memcg_data & MEMCG_DATA_KMEM;
}

diff --git a/init/Kconfig b/init/Kconfig
index 532362fcfe31..82396d7a2717 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -958,6 +958,10 @@ config MEMCG
help
Provides control over the memory footprint of tasks in a cgroup.

+config SLAB_OBJ_EXT
+ bool
+ depends on MEMCG
+
config MEMCG_SWAP
bool
depends on MEMCG && SWAP
@@ -966,6 +970,7 @@ config MEMCG_SWAP
config MEMCG_KMEM
bool
depends on MEMCG && !SLOB
+ select SLAB_OBJ_EXT
default y

config BLK_CGROUP
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index c252081b11df..c0958e4a32e2 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -569,7 +569,7 @@ static unsigned long kfence_init_pool(void)
__folio_set_slab(slab_folio(slab));
#ifdef CONFIG_MEMCG
slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
- MEMCG_DATA_OBJCGS;
+ MEMCG_DATA_OBJEXTS;
#endif
}

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b69979c9ced5..3f407ef2f3f1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2793,7 +2793,7 @@ static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
folio->memcg_data = (unsigned long)memcg;
}

-#ifdef CONFIG_MEMCG_KMEM
+#ifdef CONFIG_SLAB_OBJ_EXT
/*
* The allocated objcg pointers array is not accounted directly.
* Moreover, it should not come from DMA buffer and is not readily
@@ -2801,38 +2801,20 @@ static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
*/
#define OBJCGS_CLEAR_MASK (__GFP_DMA | __GFP_RECLAIMABLE | __GFP_ACCOUNT)

-/*
- * mod_objcg_mlstate() may be called with irq enabled, so
- * mod_memcg_lruvec_state() should be used.
- */
-static inline void mod_objcg_mlstate(struct obj_cgroup *objcg,
- struct pglist_data *pgdat,
- enum node_stat_item idx, int nr)
-{
- struct mem_cgroup *memcg;
- struct lruvec *lruvec;
-
- rcu_read_lock();
- memcg = obj_cgroup_memcg(objcg);
- lruvec = mem_cgroup_lruvec(memcg, pgdat);
- mod_memcg_lruvec_state(lruvec, idx, nr);
- rcu_read_unlock();
-}
-
-int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
- gfp_t gfp, bool new_slab)
+int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
+ gfp_t gfp, bool new_slab)
{
unsigned int objects = objs_per_slab(s, slab);
unsigned long memcg_data;
void *vec;

gfp &= ~OBJCGS_CLEAR_MASK;
- vec = kcalloc_node(objects, sizeof(struct obj_cgroup *), gfp,
+ vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
slab_nid(slab));
if (!vec)
return -ENOMEM;

- memcg_data = (unsigned long) vec | MEMCG_DATA_OBJCGS;
+ memcg_data = (unsigned long) vec | MEMCG_DATA_OBJEXTS;
if (new_slab) {
/*
* If the slab is brand new and nobody can yet access its
@@ -2843,7 +2825,7 @@ int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
} else if (cmpxchg(&slab->memcg_data, 0, memcg_data)) {
/*
* If the slab is already in use, somebody can allocate and
- * assign obj_cgroups in parallel. In this case the existing
+ * assign slabobj_exts in parallel. In this case the existing
* objcg vector should be reused.
*/
kfree(vec);
@@ -2853,6 +2835,26 @@ int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
kmemleak_not_leak(vec);
return 0;
}
+#endif /* CONFIG_SLAB_OBJ_EXT */
+
+#ifdef CONFIG_MEMCG_KMEM
+/*
+ * mod_objcg_mlstate() may be called with irq enabled, so
+ * mod_memcg_lruvec_state() should be used.
+ */
+static inline void mod_objcg_mlstate(struct obj_cgroup *objcg,
+ struct pglist_data *pgdat,
+ enum node_stat_item idx, int nr)
+{
+ struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
+
+ rcu_read_lock();
+ memcg = obj_cgroup_memcg(objcg);
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
+ mod_memcg_lruvec_state(lruvec, idx, nr);
+ rcu_read_unlock();
+}

static __always_inline
struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, void *p)
@@ -2863,18 +2865,18 @@ struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, void *p)
* slab->memcg_data.
*/
if (folio_test_slab(folio)) {
- struct obj_cgroup **objcgs;
+ struct slabobj_ext *obj_exts;
struct slab *slab;
unsigned int off;

slab = folio_slab(folio);
- objcgs = slab_objcgs(slab);
- if (!objcgs)
+ obj_exts = slab_obj_exts(slab);
+ if (!obj_exts)
return NULL;

off = obj_to_index(slab->slab_cache, slab, p);
- if (objcgs[off])
- return obj_cgroup_memcg(objcgs[off]);
+ if (obj_exts[off].objcg)
+ return obj_cgroup_memcg(obj_exts[off].objcg);

return NULL;
}
diff --git a/mm/page_owner.c b/mm/page_owner.c
index e4c6f3f1695b..fd4af1ad34b8 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -353,7 +353,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret,
if (!memcg_data)
goto out_unlock;

- if (memcg_data & MEMCG_DATA_OBJCGS)
+ if (memcg_data & MEMCG_DATA_OBJEXTS)
ret += scnprintf(kbuf + ret, count - ret,
"Slab cache page\n");

diff --git a/mm/slab.h b/mm/slab.h
index 4ec82bec15ec..c767ce3f0fe2 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -422,36 +422,94 @@ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t fla
return false;
}

+#ifdef CONFIG_SLAB_OBJ_EXT
+
+static inline bool is_kmem_only_obj_ext(void)
+{
#ifdef CONFIG_MEMCG_KMEM
+ return sizeof(struct slabobj_ext) == sizeof(struct obj_cgroup *);
+#else
+ return false;
+#endif
+}
+
/*
- * slab_objcgs - get the object cgroups vector associated with a slab
+ * slab_obj_exts - get the pointer to the slab object extension vector
+ * associated with a slab.
* @slab: a pointer to the slab struct
*
- * Returns a pointer to the object cgroups vector associated with the slab,
+ * Returns a pointer to the object extension vector associated with the slab,
* or NULL if no such vector has been associated yet.
*/
-static inline struct obj_cgroup **slab_objcgs(struct slab *slab)
+static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
{
unsigned long memcg_data = READ_ONCE(slab->memcg_data);

- VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS),
+ VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJEXTS),
slab_page(slab));
VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, slab_page(slab));

- return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+ return (struct slabobj_ext *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
}

-int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
- gfp_t gfp, bool new_slab);
-void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
- enum node_stat_item idx, int nr);
+int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
+ gfp_t gfp, bool new_slab);

-static inline void memcg_free_slab_cgroups(struct slab *slab)
+static inline void free_slab_obj_exts(struct slab *slab)
{
- kfree(slab_objcgs(slab));
+ struct slabobj_ext *obj_exts;
+
+ if (!memcg_kmem_enabled() && is_kmem_only_obj_ext())
+ return;
+
+ obj_exts = slab_obj_exts(slab);
+ kfree(obj_exts);
slab->memcg_data = 0;
}

+static inline void prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
+{
+ struct slab *slab;
+
+ /* If kmem is the only extension then the vector will be created conditionally */
+ if (is_kmem_only_obj_ext())
+ return;
+
+ slab = virt_to_slab(p);
+ if (!slab_obj_exts(slab))
+ WARN(alloc_slab_obj_exts(slab, s, flags, false),
+ "%s, %s: Failed to create slab extension vector!\n",
+ __func__, s->name);
+}
+
+#else /* CONFIG_SLAB_OBJ_EXT */
+
+static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
+{
+ return NULL;
+}
+
+static inline int alloc_slab_obj_exts(struct slab *slab,
+ struct kmem_cache *s, gfp_t gfp,
+ bool new_slab)
+{
+ return 0;
+}
+
+static inline void free_slab_obj_exts(struct slab *slab)
+{
+}
+
+static inline void prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
+{
+}
+
+#endif /* CONFIG_SLAB_OBJ_EXT */
+
+#ifdef CONFIG_MEMCG_KMEM
+void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
+ enum node_stat_item idx, int nr);
+
static inline size_t obj_full_size(struct kmem_cache *s)
{
/*
@@ -519,16 +577,15 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
if (likely(p[i])) {
slab = virt_to_slab(p[i]);

- if (!slab_objcgs(slab) &&
- memcg_alloc_slab_cgroups(slab, s, flags,
- false)) {
+ if (!slab_obj_exts(slab) &&
+ alloc_slab_obj_exts(slab, s, flags, false)) {
obj_cgroup_uncharge(objcg, obj_full_size(s));
continue;
}

off = obj_to_index(s, slab, p[i]);
obj_cgroup_get(objcg);
- slab_objcgs(slab)[off] = objcg;
+ slab_obj_exts(slab)[off].objcg = objcg;
mod_objcg_state(objcg, slab_pgdat(slab),
cache_vmstat_idx(s), obj_full_size(s));
} else {
@@ -541,14 +598,14 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects)
{
- struct obj_cgroup **objcgs;
+ struct slabobj_ext *obj_exts;
int i;

if (!memcg_kmem_enabled())
return;

- objcgs = slab_objcgs(slab);
- if (!objcgs)
+ obj_exts = slab_obj_exts(slab);
+ if (!obj_exts)
return;

for (i = 0; i < objects; i++) {
@@ -556,11 +613,11 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
unsigned int off;

off = obj_to_index(s, slab, p[i]);
- objcg = objcgs[off];
+ objcg = obj_exts[off].objcg;
if (!objcg)
continue;

- objcgs[off] = NULL;
+ obj_exts[off].objcg = NULL;
obj_cgroup_uncharge(objcg, obj_full_size(s));
mod_objcg_state(objcg, slab_pgdat(slab), cache_vmstat_idx(s),
-obj_full_size(s));
@@ -569,27 +626,11 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
}

#else /* CONFIG_MEMCG_KMEM */
-static inline struct obj_cgroup **slab_objcgs(struct slab *slab)
-{
- return NULL;
-}
-
static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
{
return NULL;
}

-static inline int memcg_alloc_slab_cgroups(struct slab *slab,
- struct kmem_cache *s, gfp_t gfp,
- bool new_slab)
-{
- return 0;
-}
-
-static inline void memcg_free_slab_cgroups(struct slab *slab)
-{
-}
-
static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s,
struct list_lru *lru,
struct obj_cgroup **objcgp,
@@ -627,7 +668,7 @@ static __always_inline void account_slab(struct slab *slab, int order,
struct kmem_cache *s, gfp_t gfp)
{
if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT))
- memcg_alloc_slab_cgroups(slab, s, gfp, true);
+ alloc_slab_obj_exts(slab, s, gfp, true);

mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
PAGE_SIZE << order);
@@ -636,8 +677,7 @@ static __always_inline void account_slab(struct slab *slab, int order,
static __always_inline void unaccount_slab(struct slab *slab, int order,
struct kmem_cache *s)
{
- if (memcg_kmem_enabled())
- memcg_free_slab_cgroups(slab);
+ free_slab_obj_exts(slab);

mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
-(PAGE_SIZE << order));
@@ -729,6 +769,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
memset(p[i], 0, s->object_size);
kmemleak_alloc_recursive(p[i], s->object_size, 1,
s->flags, flags);
+ prepare_slab_obj_exts_hook(s, flags, p[i]);
}

memcg_slab_post_alloc_hook(s, objcg, flags, size, p);
--
2.37.2.672.g94769d06f0-goog