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From:   Roman Gushchin <guro@fb.com>
To:     Andrew Morton <akpm@linux-foundation.org>
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Subject: Re: [PATCH v3 07/19] mm: memcg/slab: allocate obj_cgroups for
 non-root slab pages
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On Wed, Apr 22, 2020 at 01:46:56PM -0700, Roman Gushchin wrote:
> 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/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
> 


Ooops, the build bot found that objs_per_slab() was accidentally guarded by
CONFIG_SLUB_DEBUG. An updated version below.

--

From 6b358e0157815535c3a73b4ce7b28f9c4c7804b3 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <guro@fb.com>
Date: Wed, 10 Jul 2019 15:44:38 -0700
Subject: [PATCH v3.1 07/19] mm: memcg/slab: allocate obj_cgroups for non-root
 slab pages

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..a5fb0bb5c77a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -344,6 +344,11 @@ static inline unsigned int oo_objects(struct kmem_cache_order_objects x)
 	return x.x & OO_MASK;
 }
 
+int objs_per_slab(struct kmem_cache *cache)
+{
+	return oo_objects(cache->oo);
+}
+
 /*
  * Per slab locking using the pagelock
  */
-- 
2.25.3