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Subject[PATCH v3 07/19] mm: memcg/slab: allocate obj_cgroups for non-root slab pages
Date
Allocate and release memory to store obj_cgroup pointers for each
non-root slab page. Reuse page->mem_cgroup pointer to store a pointer
to the allocated space.

To distinguish between obj_cgroups and memcg pointers in case
when it's not obvious which one is used (as in page_cgroup_ino()),
let's always set the lowest bit in the obj_cgroup case.

Signed-off-by: Roman Gushchin <guro@fb.com>
---
include/linux/mm_types.h | 5 ++++-
include/linux/slab_def.h | 5 +++++
include/linux/slub_def.h | 2 ++
mm/memcontrol.c | 17 +++++++++++---
mm/slab.c | 3 ++-
mm/slab.h | 48 ++++++++++++++++++++++++++++++++++++++++
mm/slub.c | 5 +++++
7 files changed, 80 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4aba6c0c2ba8..0ad7e700f26d 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -198,7 +198,10 @@ struct page {
atomic_t _refcount;

#ifdef CONFIG_MEMCG
- struct mem_cgroup *mem_cgroup;
+ union {
+ struct mem_cgroup *mem_cgroup;
+ struct obj_cgroup **obj_cgroups;
+ };
#endif

/*
diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
index abc7de77b988..967a9a525eab 100644
--- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -114,4 +114,9 @@ static inline unsigned int obj_to_index(const struct kmem_cache *cache,
return reciprocal_divide(offset, cache->reciprocal_buffer_size);
}

+static inline int objs_per_slab(const struct kmem_cache *cache)
+{
+ return cache->num;
+}
+
#endif /* _LINUX_SLAB_DEF_H */
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 200ea292f250..cbda7d55796a 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -191,4 +191,6 @@ static inline unsigned int obj_to_index(const struct kmem_cache *cache,
cache->reciprocal_size);
}

+extern int objs_per_slab(struct kmem_cache *cache);
+
#endif /* _LINUX_SLUB_DEF_H */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7f87a0eeafec..63826e460b3f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -549,10 +549,21 @@ ino_t page_cgroup_ino(struct page *page)
unsigned long ino = 0;

rcu_read_lock();
- if (PageSlab(page) && !PageTail(page))
+ if (PageSlab(page) && !PageTail(page)) {
memcg = memcg_from_slab_page(page);
- else
- memcg = READ_ONCE(page->mem_cgroup);
+ } else {
+ 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;
+ }
+
while (memcg && !(memcg->css.flags & CSS_ONLINE))
memcg = parent_mem_cgroup(memcg);
if (memcg)
diff --git a/mm/slab.c b/mm/slab.c
index 9350062ffc1a..f2d67984595b 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1370,7 +1370,8 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
return NULL;
}

- if (charge_slab_page(page, flags, cachep->gfporder, cachep)) {
+ if (charge_slab_page(page, flags, cachep->gfporder, cachep,
+ cachep->num)) {
__free_pages(page, cachep->gfporder);
return NULL;
}
diff --git a/mm/slab.h b/mm/slab.h
index 8a574d9361c1..44def57f050e 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -319,6 +319,18 @@ static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
return s->memcg_params.root_cache;
}

+static inline struct obj_cgroup **page_obj_cgroups(struct page *page)
+{
+ /*
+ * page->mem_cgroup and page->obj_cgroups are sharing the same
+ * space. To distinguish between them in case we don't know for sure
+ * that the page is a slab page (e.g. page_cgroup_ino()), let's
+ * always set the lowest bit of obj_cgroups.
+ */
+ return (struct obj_cgroup **)
+ ((unsigned long)page->obj_cgroups & ~0x1UL);
+}
+
/*
* Expects a pointer to a slab page. Please note, that PageSlab() check
* isn't sufficient, as it returns true also for tail compound slab pages,
@@ -406,6 +418,25 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
percpu_ref_put_many(&s->memcg_params.refcnt, nr_pages);
}

+static inline int memcg_alloc_page_obj_cgroups(struct page *page, gfp_t gfp,
+ unsigned int objects)
+{
+ void *vec;
+
+ vec = kcalloc(objects, sizeof(struct obj_cgroup *), gfp);
+ if (!vec)
+ return -ENOMEM;
+
+ page->obj_cgroups = (struct obj_cgroup **) ((unsigned long)vec | 0x1UL);
+ return 0;
+}
+
+static inline void memcg_free_page_obj_cgroups(struct page *page)
+{
+ kfree(page_obj_cgroups(page));
+ page->obj_cgroups = NULL;
+}
+
extern void slab_init_memcg_params(struct kmem_cache *);
extern void memcg_link_cache(struct kmem_cache *s, struct mem_cgroup *memcg);

@@ -455,6 +486,16 @@ static inline void memcg_uncharge_slab(struct page *page, int order,
{
}

+static inline int memcg_alloc_page_obj_cgroups(struct page *page, gfp_t gfp,
+ unsigned int objects)
+{
+ return 0;
+}
+
+static inline void memcg_free_page_obj_cgroups(struct page *page)
+{
+}
+
static inline void slab_init_memcg_params(struct kmem_cache *s)
{
}
@@ -481,12 +522,18 @@ static __always_inline int charge_slab_page(struct page *page,
gfp_t gfp, int order,
struct kmem_cache *s)
{
+ int ret;
+
if (is_root_cache(s)) {
mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
PAGE_SIZE << order);
return 0;
}

+ ret = memcg_alloc_page_obj_cgroups(page, gfp, objs_per_slab(s));
+ if (ret)
+ return ret;
+
return memcg_charge_slab(page, gfp, order, s);
}

@@ -499,6 +546,7 @@ static __always_inline void uncharge_slab_page(struct page *page, int order,
return;
}

+ memcg_free_page_obj_cgroups(page);
memcg_uncharge_slab(page, order, s);
}

diff --git a/mm/slub.c b/mm/slub.c
index 8d16babe1829..68c2c45dfac1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5992,4 +5992,9 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
{
return -EIO;
}
+
+int objs_per_slab(struct kmem_cache *cache)
+{
+ return oo_objects(cache->oo);
+}
#endif /* CONFIG_SLUB_DEBUG */
--
2.25.3
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