[PATCH v5 0/2] Directed kmem charging

[PATCH v5 0/2] Directed kmem charging

[Shakeel Butt]

This patchset introduces memcg variant memory allocation functions. The
caller can explicitly pass the memcg to charge for kmem allocations.
Currently the kernel, for __GFP_ACCOUNT memory allocation requests,
extract the memcg of the current task to charge for the kmem allocation.
This patch series introduces kmem allocation functions where the caller
can pass the pointer to the remote memcg. The remote memcg will be
charged for the allocation instead of the memcg of the caller. However
the caller must have a reference to the remote memcg.

Fixed the build for SLOB in v2, added the target_memcg in task_struct in
v3, added node variant for kmem allocation functions and rebased fsnotify
patch over Jan's patches in v4 and in v5 fixed CONFIG_MEMCG=n build and
removed the extra branch in the common case of memory allocation.

Shakeel Butt (2):
  mm: memcg: remote memcg charging for kmem allocations
  fs: fsnotify: account fsnotify metadata to kmemcg

 fs/notify/dnotify/dnotify.c          |  5 ++-
 fs/notify/fanotify/fanotify.c        |  6 ++-
 fs/notify/fanotify/fanotify_user.c   |  5 ++-
 fs/notify/group.c                    |  4 ++
 fs/notify/inotify/inotify_fsnotify.c |  2 +-
 fs/notify/inotify/inotify_user.c     |  5 ++-
 include/linux/fsnotify_backend.h     | 12 ++++--
 include/linux/memcontrol.h           |  7 ++++
 include/linux/sched.h                |  3 ++
 include/linux/sched/mm.h             | 24 +++++++++++
 include/linux/slab.h                 | 59 ++++++++++++++++++++++++++++
 kernel/fork.c                        |  3 ++
 mm/memcontrol.c                      | 20 ++++++++--
 13 files changed, 141 insertions(+), 14 deletions(-)

-- 
2.17.0.484.g0c8726318c-goog

[PATCH v5 1/2] mm: memcg: remote memcg charging for kmem allocations

[Shakeel Butt]

Introduce the memcg variant for kmalloc[_node] and
kmem_cache_alloc[_node].  For kmem_cache_alloc, the kernel switches the
root kmem cache with the memcg specific kmem cache for __GFP_ACCOUNT
allocations to charge those allocations to the memcg.  However, the memcg
to charge is extracted from the current task_struct.  This patch
introduces the variant of kmem cache allocation functions where the memcg
can be provided explicitly by the caller instead of deducing the memcg
from the current task.

The kmalloc allocations are underlying served using the kmem caches unless
the size of the allocation request is larger than KMALLOC_MAX_CACHE_SIZE,
in which case, the kmem caches are bypassed and the request is routed
directly to page allocator.  So, for __GFP_ACCOUNT kmalloc allocations,
the memcg of current task is charged.  This patch introduces memcg variant
of kmalloc functions to allow callers to provide memcg for charging.

These functions are useful for use-cases where the allocations should be
charged to the memcg different from the memcg of the caller.  One such
concrete use-case is the allocations for fsnotify event objects where the
objects should be charged to the listener instead of the producer.

One requirement to call these functions is that the caller must have the
reference to the memcg.  Using kmalloc_memcg and kmem_cache_alloc_memcg
implicitly assumes that the caller is requesting a __GFP_ACCOUNT
allocation.

Signed-off-by: Shakeel Butt <shakeelb@google.com>
---
Changelog since v4:
- Removed branch from hot path of memory charging.

Changelog since v3:
- Added node variant of directed kmem allocation functions.

Changelog since v2:
- Merge the kmalloc_memcg patch into this patch.
- Instead of plumbing memcg throughout, use field in task_struct to pass
  the target_memcg.

Changelog since v1:
- Fixed build for SLOB

 include/linux/sched.h    |  3 ++
 include/linux/sched/mm.h | 24 ++++++++++++++++
 include/linux/slab.h     | 59 ++++++++++++++++++++++++++++++++++++++++
 kernel/fork.c            |  3 ++
 mm/memcontrol.c          | 18 ++++++++++--
 5 files changed, 105 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b3d697f3b573..d0b8c3ee717b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1097,6 +1097,9 @@ struct task_struct {
 
 	/* Number of pages to reclaim on returning to userland: */
 	unsigned int			memcg_nr_pages_over_high;
+
+	/* Used by memcontrol for targeted memcg charge: */
+	struct mem_cgroup		*target_memcg;
 #endif
 
 #ifdef CONFIG_UPROBES
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 2c570cd934af..333f620a4634 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -206,6 +206,30 @@ static inline void memalloc_noreclaim_restore(unsigned int flags)
 	current->flags = (current->flags & ~PF_MEMALLOC) | flags;
 }
 
+#ifdef CONFIG_MEMCG
+static inline struct mem_cgroup *memalloc_memcg_save(struct mem_cgroup *memcg)
+{
+	struct mem_cgroup *old_memcg = current->target_memcg;
+
+	current->target_memcg = memcg;
+	return old_memcg;
+}
+
+static inline void memalloc_memcg_restore(struct mem_cgroup *memcg)
+{
+	current->target_memcg = memcg;
+}
+#else
+static inline struct mem_cgroup *memalloc_memcg_save(struct mem_cgroup *memcg)
+{
+	return NULL;
+}
+
+static inline void memalloc_memcg_restore(struct mem_cgroup *memcg)
+{
+}
+#endif /* CONFIG_MEMCG */
+
 #ifdef CONFIG_MEMBARRIER
 enum {
 	MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY		= (1U << 0),
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 81ebd71f8c03..9ebe659bd4a5 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -15,6 +15,7 @@
 #include <linux/gfp.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/sched/mm.h>
 
 
 /*
@@ -374,6 +375,21 @@ static __always_inline void kfree_bulk(size_t size, void **p)
 	kmem_cache_free_bulk(NULL, size, p);
 }
 
+/*
+ * Calling kmem_cache_alloc_memcg implicitly assumes that the caller
+ * wants a __GFP_ACCOUNT allocation.
+ */
+static __always_inline void *kmem_cache_alloc_memcg(struct kmem_cache *cachep,
+						    gfp_t flags,
+						    struct mem_cgroup *memcg)
+{
+	struct mem_cgroup *old_memcg = memalloc_memcg_save(memcg);
+	void *ptr = kmem_cache_alloc(cachep, flags | __GFP_ACCOUNT);
+
+	memalloc_memcg_restore(old_memcg);
+	return ptr;
+}
+
 #ifdef CONFIG_NUMA
 void *__kmalloc_node(size_t size, gfp_t flags, int node) __assume_kmalloc_alignment __malloc;
 void *kmem_cache_alloc_node(struct kmem_cache *, gfp_t flags, int node) __assume_slab_alignment __malloc;
@@ -389,6 +405,21 @@ static __always_inline void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t f
 }
 #endif
 
+/*
+ * Calling kmem_cache_alloc_node_memcg implicitly assumes that the caller
+ * wants a __GFP_ACCOUNT allocation.
+ */
+static __always_inline void *
+kmem_cache_alloc_node_memcg(struct kmem_cache *cachep, gfp_t flags, int node,
+			    struct mem_cgroup *memcg)
+{
+	struct mem_cgroup *old_memcg = memalloc_memcg_save(memcg);
+	void *ptr = kmem_cache_alloc_node(cachep, flags | __GFP_ACCOUNT, node);
+
+	memalloc_memcg_restore(old_memcg);
+	return ptr;
+}
+
 #ifdef CONFIG_TRACING
 extern void *kmem_cache_alloc_trace(struct kmem_cache *, gfp_t, size_t) __assume_slab_alignment __malloc;
 
@@ -517,6 +548,20 @@ static __always_inline void *kmalloc(size_t size, gfp_t flags)
 	return __kmalloc(size, flags);
 }
 
+/*
+ * Calling kmalloc_memcg implicitly assumes that the caller wants a
+ * __GFP_ACCOUNT allocation.
+ */
+static __always_inline void *kmalloc_memcg(size_t size, gfp_t flags,
+					   struct mem_cgroup *memcg)
+{
+	struct mem_cgroup *old_memcg = memalloc_memcg_save(memcg);
+	void *ptr = kmalloc(size, flags | __GFP_ACCOUNT);
+
+	memalloc_memcg_restore(old_memcg);
+	return ptr;
+}
+
 /*
  * Determine size used for the nth kmalloc cache.
  * return size or 0 if a kmalloc cache for that
@@ -554,6 +599,20 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
 	return __kmalloc_node(size, flags, node);
 }
 
+/*
+ * Calling kmalloc_node_memcg implicitly assumes that the caller wants a
+ * __GFP_ACCOUNT allocation.
+ */
+static __always_inline void *
+kmalloc_node_memcg(size_t size, gfp_t flags, int node, struct mem_cgroup *memcg)
+{
+	struct mem_cgroup *old_memcg = memalloc_memcg_save(memcg);
+	void *ptr = kmalloc_node(size, flags | __GFP_ACCOUNT, node);
+
+	memalloc_memcg_restore(old_memcg);
+	return ptr;
+}
+
 struct memcg_cache_array {
 	struct rcu_head rcu;
 	struct kmem_cache *entries[0];
diff --git a/kernel/fork.c b/kernel/fork.c
index ff0e0477c1bb..b1d877f1a0ac 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -835,6 +835,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	tsk->fail_nth = 0;
 #endif
 
+#ifdef CONFIG_MEMCG
+	tsk->target_memcg = NULL;
+#endif
 	return tsk;
 
 free_stack:
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d455bc08eb55..2c5f6b8819d9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -701,6 +701,20 @@ static struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 	return memcg;
 }
 
+static __always_inline struct mem_cgroup *get_mem_cgroup(
+				struct mem_cgroup *memcg, struct mm_struct *mm)
+{
+	if (unlikely(memcg)) {
+		rcu_read_lock();
+		if (css_tryget_online(&memcg->css)) {
+			rcu_read_unlock();
+			return memcg;
+		}
+		rcu_read_unlock();
+	}
+	return get_mem_cgroup_from_mm(mm);
+}
+
 /**
  * mem_cgroup_iter - iterate over memory cgroup hierarchy
  * @root: hierarchy root
@@ -2260,7 +2274,7 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
 	if (current->memcg_kmem_skip_account)
 		return cachep;
 
-	memcg = get_mem_cgroup_from_mm(current->mm);
+	memcg = get_mem_cgroup(current->target_memcg, current->mm);
 	kmemcg_id = READ_ONCE(memcg->kmemcg_id);
 	if (kmemcg_id < 0)
 		goto out;
@@ -2344,7 +2358,7 @@ int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
 	if (memcg_kmem_bypass())
 		return 0;
 
-	memcg = get_mem_cgroup_from_mm(current->mm);
+	memcg = get_mem_cgroup(current->target_memcg, current->mm);
 	if (!mem_cgroup_is_root(memcg)) {
 		ret = memcg_kmem_charge_memcg(page, gfp, order, memcg);
 		if (!ret)
-- 
2.17.0.484.g0c8726318c-goog

Re: [PATCH v5 1/2] mm: memcg: remote memcg charging for kmem allocations

[Shakeel Butt]

On Mon, Apr 16, 2018 at 1:51 PM, Shakeel Butt <shakeelb@google.com> wrote:
> Introduce the memcg variant for kmalloc[_node] and
> kmem_cache_alloc[_node].  For kmem_cache_alloc, the kernel switches the
> root kmem cache with the memcg specific kmem cache for __GFP_ACCOUNT
> allocations to charge those allocations to the memcg.  However, the memcg
> to charge is extracted from the current task_struct.  This patch
> introduces the variant of kmem cache allocation functions where the memcg
> can be provided explicitly by the caller instead of deducing the memcg
> from the current task.
>
> The kmalloc allocations are underlying served using the kmem caches unless
> the size of the allocation request is larger than KMALLOC_MAX_CACHE_SIZE,
> in which case, the kmem caches are bypassed and the request is routed
> directly to page allocator.  So, for __GFP_ACCOUNT kmalloc allocations,
> the memcg of current task is charged.  This patch introduces memcg variant
> of kmalloc functions to allow callers to provide memcg for charging.
>
> These functions are useful for use-cases where the allocations should be
> charged to the memcg different from the memcg of the caller.  One such
> concrete use-case is the allocations for fsnotify event objects where the
> objects should be charged to the listener instead of the producer.
>
> One requirement to call these functions is that the caller must have the
> reference to the memcg.  Using kmalloc_memcg and kmem_cache_alloc_memcg
> implicitly assumes that the caller is requesting a __GFP_ACCOUNT
> allocation.
>
> Signed-off-by: Shakeel Butt <shakeelb@google.com>

I will send the v6 of this patchset after this merge window. In v6, I
will make memalloc_memcg_[save|restore] scope API similar to NOFS,
NOIO and NORECLAIM APIs.

> ---
> Changelog since v4:
> - Removed branch from hot path of memory charging.
>
> Changelog since v3:
> - Added node variant of directed kmem allocation functions.
>
> Changelog since v2:
> - Merge the kmalloc_memcg patch into this patch.
> - Instead of plumbing memcg throughout, use field in task_struct to pass
>   the target_memcg.
>
> Changelog since v1:
> - Fixed build for SLOB
>

[PATCH v5 2/2] fs: fsnotify: account fsnotify metadata to kmemcg

[Shakeel Butt]

A lot of memory can be consumed by the events generated for the huge or
unlimited queues if there is either no or slow listener.  This can cause
system level memory pressure or OOMs.  So, it's better to account the
fsnotify kmem caches to the memcg of the listener.

There are seven fsnotify kmem caches and among them allocations from
dnotify_struct_cache, dnotify_mark_cache, fanotify_mark_cache and
inotify_inode_mark_cachep happens in the context of syscall from the
listener.  So, SLAB_ACCOUNT is enough for these caches.

The objects from fsnotify_mark_connector_cachep are not accounted as they
are small compared to the notification mark or events and it is unclear
whom to account connector to since it is shared by all events attached to
the inode.

The allocations from the event caches happen in the context of the event
producer.  For such caches we will need to remote charge the allocations
to the listener's memcg.  Thus we save the memcg reference in the
fsnotify_group structure of the listener.

This patch has also moved the members of fsnotify_group to keep the size
same, at least for 64 bit build, even with additional member by filling
the holes.

Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Jan Kara <jack@suse.cz>
---
Changelog since v4:
- Fixed the build for CONFIG_MEMCG=n

Changelog since v3:
- Rebased over Jan's patches.
- Some cleanup based on Amir's comments.

Changelog since v2:
- None

Changelog since v1:
- no more charging fsnotify_mark_connector objects
- Fixed the build for SLOB

 fs/notify/dnotify/dnotify.c          |  5 +++--
 fs/notify/fanotify/fanotify.c        |  6 ++++--
 fs/notify/fanotify/fanotify_user.c   |  5 ++++-
 fs/notify/group.c                    |  4 ++++
 fs/notify/inotify/inotify_fsnotify.c |  2 +-
 fs/notify/inotify/inotify_user.c     |  5 ++++-
 include/linux/fsnotify_backend.h     | 12 ++++++++----
 include/linux/memcontrol.h           |  7 +++++++
 mm/memcontrol.c                      |  2 +-
 9 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
index 63a1ca4b9dee..eb5c41284649 100644
--- a/fs/notify/dnotify/dnotify.c
+++ b/fs/notify/dnotify/dnotify.c
@@ -384,8 +384,9 @@ int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
 
 static int __init dnotify_init(void)
 {
-	dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
-	dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
+	dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
+					  SLAB_PANIC|SLAB_ACCOUNT);
+	dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
 
 	dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
 	if (IS_ERR(dnotify_group))
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index d94e8031fe5f..78cfdcfd9f8e 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -153,14 +153,16 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
 	if (fanotify_is_perm_event(mask)) {
 		struct fanotify_perm_event_info *pevent;
 
-		pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
+		pevent = kmem_cache_alloc_memcg(fanotify_perm_event_cachep, gfp,
+						group->memcg);
 		if (!pevent)
 			return NULL;
 		event = &pevent->fae;
 		pevent->response = 0;
 		goto init;
 	}
-	event = kmem_cache_alloc(fanotify_event_cachep, gfp);
+	event = kmem_cache_alloc_memcg(fanotify_event_cachep, gfp,
+				       group->memcg);
 	if (!event)
 		return NULL;
 init: __maybe_unused
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index ec4d8c59d0e3..0cf45041dc32 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -16,6 +16,7 @@
 #include <linux/uaccess.h>
 #include <linux/compat.h>
 #include <linux/sched/signal.h>
+#include <linux/memcontrol.h>
 
 #include <asm/ioctls.h>
 
@@ -756,6 +757,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 
 	group->fanotify_data.user = user;
 	atomic_inc(&user->fanotify_listeners);
+	group->memcg = get_mem_cgroup_from_mm(current->mm);
 
 	oevent = fanotify_alloc_event(group, NULL, FS_Q_OVERFLOW, NULL);
 	if (unlikely(!oevent)) {
@@ -957,7 +959,8 @@ COMPAT_SYSCALL_DEFINE6(fanotify_mark,
  */
 static int __init fanotify_user_setup(void)
 {
-	fanotify_mark_cache = KMEM_CACHE(fsnotify_mark, SLAB_PANIC);
+	fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,
+					 SLAB_PANIC|SLAB_ACCOUNT);
 	fanotify_event_cachep = KMEM_CACHE(fanotify_event_info, SLAB_PANIC);
 	if (IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS)) {
 		fanotify_perm_event_cachep =
diff --git a/fs/notify/group.c b/fs/notify/group.c
index b7a4b6a69efa..3e56459f4773 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -22,6 +22,7 @@
 #include <linux/srcu.h>
 #include <linux/rculist.h>
 #include <linux/wait.h>
+#include <linux/memcontrol.h>
 
 #include <linux/fsnotify_backend.h>
 #include "fsnotify.h"
@@ -36,6 +37,9 @@ static void fsnotify_final_destroy_group(struct fsnotify_group *group)
 	if (group->ops->free_group_priv)
 		group->ops->free_group_priv(group);
 
+	if (group->memcg)
+		mem_cgroup_put(group->memcg);
+
 	kfree(group);
 }
 
diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index 40dedb37a1f3..b184bff93d02 100644
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -98,7 +98,7 @@ int inotify_handle_event(struct fsnotify_group *group,
 	i_mark = container_of(inode_mark, struct inotify_inode_mark,
 			      fsn_mark);
 
-	event = kmalloc(alloc_len, GFP_KERNEL);
+	event = kmalloc_memcg(alloc_len, GFP_KERNEL, group->memcg);
 	if (unlikely(!event)) {
 		/*
 		 * Treat lost event due to ENOMEM the same way as queue
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index ef32f3657958..3c152e350805 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -38,6 +38,7 @@
 #include <linux/uaccess.h>
 #include <linux/poll.h>
 #include <linux/wait.h>
+#include <linux/memcontrol.h>
 
 #include "inotify.h"
 #include "../fdinfo.h"
@@ -632,6 +633,7 @@ static struct fsnotify_group *inotify_new_group(unsigned int max_events)
 	oevent->name_len = 0;
 
 	group->max_events = max_events;
+	group->memcg = get_mem_cgroup_from_mm(current->mm);
 
 	spin_lock_init(&group->inotify_data.idr_lock);
 	idr_init(&group->inotify_data.idr);
@@ -804,7 +806,8 @@ static int __init inotify_user_setup(void)
 
 	BUG_ON(hweight32(ALL_INOTIFY_BITS) != 21);
 
-	inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark, SLAB_PANIC);
+	inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark,
+					       SLAB_PANIC|SLAB_ACCOUNT);
 
 	inotify_max_queued_events = 16384;
 	init_user_ns.ucount_max[UCOUNT_INOTIFY_INSTANCES] = 128;
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 9f1edb92c97e..81bd86dfa2cd 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -84,6 +84,8 @@ struct fsnotify_event_private_data;
 struct fsnotify_fname;
 struct fsnotify_iter_info;
 
+struct mem_cgroup;
+
 /*
  * Each group much define these ops.  The fsnotify infrastructure will call
  * these operations for each relevant group.
@@ -129,6 +131,8 @@ struct fsnotify_event {
  * everything will be cleaned up.
  */
 struct fsnotify_group {
+	const struct fsnotify_ops *ops;	/* how this group handles things */
+
 	/*
 	 * How the refcnt is used is up to each group.  When the refcnt hits 0
 	 * fsnotify will clean up all of the resources associated with this group.
@@ -139,8 +143,6 @@ struct fsnotify_group {
 	 */
 	refcount_t refcnt;		/* things with interest in this group */
 
-	const struct fsnotify_ops *ops;	/* how this group handles things */
-
 	/* needed to send notification to userspace */
 	spinlock_t notification_lock;		/* protect the notification_list */
 	struct list_head notification_list;	/* list of event_holder this group needs to send to userspace */
@@ -162,6 +164,8 @@ struct fsnotify_group {
 	atomic_t num_marks;		/* 1 for each mark and 1 for not being
 					 * past the point of no return when freeing
 					 * a group */
+	atomic_t user_waits;		/* Number of tasks waiting for user
+					 * response */
 	struct list_head marks_list;	/* all inode marks for this group */
 
 	struct fasync_struct *fsn_fa;    /* async notification */
@@ -169,8 +173,8 @@ struct fsnotify_group {
 	struct fsnotify_event *overflow_event;	/* Event we queue when the
 						 * notification list is too
 						 * full */
-	atomic_t user_waits;		/* Number of tasks waiting for user
-					 * response */
+
+	struct mem_cgroup *memcg;	/* memcg to charge allocations */
 
 	/* groups can define private fields here or use the void *private */
 	union {
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 2da009958798..af9eed2e3e04 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -356,6 +356,8 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){
 	return css ? container_of(css, struct mem_cgroup, css) : NULL;
 }
 
+struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
+
 static inline void mem_cgroup_put(struct mem_cgroup *memcg)
 {
 	css_put(&memcg->css);
@@ -813,6 +815,11 @@ static inline bool task_in_mem_cgroup(struct task_struct *task,
 	return true;
 }
 
+static inline struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
+{
+	return NULL;
+}
+
 static inline void mem_cgroup_put(struct mem_cgroup *memcg)
 {
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2c5f6b8819d9..d47d356b9087 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -678,7 +678,7 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
 }
 EXPORT_SYMBOL(mem_cgroup_from_task);
 
-static struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
+struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 {
 	struct mem_cgroup *memcg = NULL;
 
-- 
2.17.0.484.g0c8726318c-goog