[PATCH v3 0/2] Directed kmem charging

[PATCH v3 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 and added the target_memcg in task_struct
in v3.

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        | 12 ++++++-----
 fs/notify/fanotify/fanotify.h        |  3 ++-
 fs/notify/fanotify/fanotify_user.c   |  7 +++++--
 fs/notify/group.c                    |  4 ++++
 fs/notify/inotify/inotify_fsnotify.c |  2 +-
 fs/notify/inotify/inotify_user.c     |  5 ++++-
 fs/notify/mark.c                     |  6 ++++--
 include/linux/fsnotify_backend.h     | 12 +++++++----
 include/linux/memcontrol.h           |  7 +++++++
 include/linux/sched.h                |  3 +++
 include/linux/sched/mm.h             | 23 +++++++++++++++++++++
 include/linux/slab.h                 | 30 ++++++++++++++++++++++++++++
 kernel/fork.c                        |  3 +++
 mm/memcontrol.c                      | 25 ++++++++++++++++++-----
 15 files changed, 124 insertions(+), 23 deletions(-)

-- 
2.16.1.291.g4437f3f132-goog

[PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations

[Shakeel Butt]

Introducing the memcg variant for kmalloc and kmem_cache_alloc. 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 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 | 23 +++++++++++++++++++++++
 include/linux/slab.h     | 30 ++++++++++++++++++++++++++++++
 kernel/fork.c            |  3 +++
 mm/memcontrol.c          | 23 +++++++++++++++++++----
 5 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ce5a27304b03..b91dbce4d886 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1061,6 +1061,9 @@ struct task_struct {
 
 	/* Number of pages to reclaim on returning to userland: */
 	unsigned int			memcg_nr_pages_over_high;
+
+	/* Used by memcontrol for targetted 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 9806184bb3d5..322e6ed38b7c 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -204,6 +204,29 @@ 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 231abc8976c5..73382ee354d4 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;
@@ -517,6 +533,20 @@ 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
diff --git a/kernel/fork.c b/kernel/fork.c
index 505195d26744..ce2e5ba8926c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -834,6 +834,9 @@ 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 fffe502a2c7f..346a594a2f7e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -701,6 +701,15 @@ static struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 	return memcg;
 }
 
+static struct mem_cgroup *get_mem_cgroup(struct mem_cgroup *memcg)
+{
+	rcu_read_lock();
+	if (!css_tryget_online(&memcg->css))
+		memcg = NULL;
+	rcu_read_unlock();
+	return memcg;
+}
+
 /**
  * mem_cgroup_iter - iterate over memory cgroup hierarchy
  * @root: hierarchy root
@@ -2248,7 +2257,7 @@ static inline bool memcg_kmem_bypass(void)
  */
 struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
 {
-	struct mem_cgroup *memcg;
+	struct mem_cgroup *memcg = NULL;
 	struct kmem_cache *memcg_cachep;
 	int kmemcg_id;
 
@@ -2260,7 +2269,10 @@ 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);
+	if (current->target_memcg)
+		memcg = get_mem_cgroup(current->target_memcg);
+	if (!memcg)
+		memcg = get_mem_cgroup_from_mm(current->mm);
 	kmemcg_id = READ_ONCE(memcg->kmemcg_id);
 	if (kmemcg_id < 0)
 		goto out;
@@ -2338,13 +2350,16 @@ int memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
  */
 int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
 {
-	struct mem_cgroup *memcg;
+	struct mem_cgroup *memcg = NULL;
 	int ret = 0;
 
 	if (memcg_kmem_bypass())
 		return 0;
 
-	memcg = get_mem_cgroup_from_mm(current->mm);
+	if (current->target_memcg)
+		memcg = get_mem_cgroup(current->target_memcg);
+	if (!memcg)
+		memcg = get_mem_cgroup_from_mm(current->mm);
 	if (!mem_cgroup_is_root(memcg)) {
 		ret = memcg_kmem_charge_memcg(page, gfp, order, memcg);
 		if (!ret)
-- 
2.16.1.291.g4437f3f132-goog

[PATCH v3 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>
---
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        | 12 +++++++-----
 fs/notify/fanotify/fanotify.h        |  3 ++-
 fs/notify/fanotify/fanotify_user.c   |  7 +++++--
 fs/notify/group.c                    |  4 ++++
 fs/notify/inotify/inotify_fsnotify.c |  2 +-
 fs/notify/inotify/inotify_user.c     |  5 ++++-
 fs/notify/mark.c                     |  6 ++++--
 include/linux/fsnotify_backend.h     | 12 ++++++++----
 include/linux/memcontrol.h           |  7 +++++++
 mm/memcontrol.c                      |  2 +-
 11 files changed, 46 insertions(+), 19 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 6702a6a0bbb5..0d9493ebc7cd 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -140,22 +140,24 @@ static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
 }
 
 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
-						 const struct path *path)
+						 const struct path *path,
+						 struct mem_cgroup *memcg)
 {
 	struct fanotify_event_info *event;
 
 	if (fanotify_is_perm_event(mask)) {
 		struct fanotify_perm_event_info *pevent;
 
-		pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
-					  GFP_KERNEL);
+		pevent = kmem_cache_alloc_memcg(fanotify_perm_event_cachep,
+						GFP_KERNEL, memcg);
 		if (!pevent)
 			return NULL;
 		event = &pevent->fae;
 		pevent->response = 0;
 		goto init;
 	}
-	event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
+	event = kmem_cache_alloc_memcg(fanotify_event_cachep, GFP_KERNEL,
+				       memcg);
 	if (!event)
 		return NULL;
 init: __maybe_unused
@@ -210,7 +212,7 @@ static int fanotify_handle_event(struct fsnotify_group *group,
 			return 0;
 	}
 
-	event = fanotify_alloc_event(inode, mask, data);
+	event = fanotify_alloc_event(inode, mask, data, group->memcg);
 	ret = -ENOMEM;
 	if (unlikely(!event))
 		goto finish;
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 256d9d1ddea9..51b797896c87 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -53,4 +53,5 @@ static inline struct fanotify_event_info *FANOTIFY_E(struct fsnotify_event *fse)
 }
 
 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
-						 const struct path *path);
+						 const struct path *path,
+						 struct mem_cgroup *memcg);
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index ef08d64c84b8..29c9b3e57a29 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>
 
@@ -756,8 +757,9 @@ 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(NULL, FS_Q_OVERFLOW, NULL);
+	oevent = fanotify_alloc_event(NULL, FS_Q_OVERFLOW, NULL, group->memcg);
 	if (unlikely(!oevent)) {
 		fd = -ENOMEM;
 		goto out_destroy_group;
@@ -951,7 +953,8 @@ 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 8b73332735ba..ed8e7b5f3981 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))
 		return -ENOMEM;
 
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index 5c29bf16814f..e80f4656799f 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"
@@ -618,6 +619,7 @@ 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);
@@ -785,7 +787,8 @@ 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/fs/notify/mark.c b/fs/notify/mark.c
index e9191b416434..c0014d0c3783 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -432,7 +432,8 @@ int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
 static int fsnotify_attach_connector_to_object(
 				struct fsnotify_mark_connector __rcu **connp,
 				struct inode *inode,
-				struct vfsmount *mnt)
+				struct vfsmount *mnt,
+				struct fsnotify_group *group)
 {
 	struct fsnotify_mark_connector *conn;
 
@@ -517,7 +518,8 @@ static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
 	conn = fsnotify_grab_connector(connp);
 	if (!conn) {
 		spin_unlock(&mark->lock);
-		err = fsnotify_attach_connector_to_object(connp, inode, mnt);
+		err = fsnotify_attach_connector_to_object(connp, inode, mnt,
+							  mark->group);
 		if (err)
 			return err;
 		goto restart;
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 067d52e95f02..e4428e383215 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 c79cdf9f8138..4525b4404a9e 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -352,6 +352,8 @@ 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);
@@ -809,6 +811,11 @@ 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 346a594a2f7e..9cfd28760b40 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;
 
-- 
2.16.1.291.g4437f3f132-goog

Re: [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations

[Michal Hocko]

On Wed 21-02-18 14:37:56, Shakeel Butt wrote:
[...]
> +#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;
> +}

So you are relying that the caller will handle the reference counting
properly? I do not think this is a good idea. Also do we need some kind
of debugging facility to detect unbalanced save/restore scopes?

[...]
> @@ -2260,7 +2269,10 @@ 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);
> +	if (current->target_memcg)
> +		memcg = get_mem_cgroup(current->target_memcg);
> +	if (!memcg)
> +		memcg = get_mem_cgroup_from_mm(current->mm);
>  	kmemcg_id = READ_ONCE(memcg->kmemcg_id);
>  	if (kmemcg_id < 0)
>  		goto out;

You are also adding one branch for _each_ charge path even though the
usecase is rather limited.

I will have to think about this approach more. It is clearly less code
than your previous attempt but I cannot say I would be really impressed.
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations

[Shakeel Butt]

On Tue, Mar 13, 2018 at 6:49 AM, Michal Hocko <mhocko@kernel.org> wrote:
> On Wed 21-02-18 14:37:56, Shakeel Butt wrote:
> [...]
>> +#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;
>> +}
>
> So you are relying that the caller will handle the reference counting
> properly? I do not think this is a good idea.

For the fsnotify use-case, this assumption makes sense as fsnotify has
an abstraction of fsnotify_group which is created by the
person/process interested in the events and thus can be used to hold
the reference to the person/process's memcg. Another use-case I have
in mind is the filesystem mount. Basically attaching a mount with a
memcg and thus all user pages and kmem allocations (inodes, dentries)
for that mount will be charged to the attached memcg. In this use-case
the super_block is the perfect structure to hold the reference to the
memcg.

If in future we find a use-case where this assumption does not make
sense we can evolve the API and since this is kernel internal API, it
should not be hard to evolve.

> Also do we need some kind
> of debugging facility to detect unbalanced save/restore scopes?
>

I am not sure, I didn't find other similar patterns (like PF_MEMALLOC)
having debugging facility. Maybe we can add such debugging facility
when we find more users other than kmalloc & kmem_cache_alloc. Vmalloc
may be one but I could not think of a use-case for vmalloc for remote
charging, so, no need to add more code at this time.

> [...]
>> @@ -2260,7 +2269,10 @@ 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);
>> +     if (current->target_memcg)
>> +             memcg = get_mem_cgroup(current->target_memcg);
>> +     if (!memcg)
>> +             memcg = get_mem_cgroup_from_mm(current->mm);
>>       kmemcg_id = READ_ONCE(memcg->kmemcg_id);
>>       if (kmemcg_id < 0)
>>               goto out;
>
> You are also adding one branch for _each_ charge path even though the
> usecase is rather limited.
>

I understand the concern but the charging path, IMO, is much complex
than just one or couple of additional branches. I can run a simple
microbenchmark to see if there is anything noticeable here.

> I will have to think about this approach more. It is clearly less code
> than your previous attempt but I cannot say I would be really impressed.
>

Thanks for your time.

Re: [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations

[Michal Hocko]

On Tue 13-03-18 10:55:18, Shakeel Butt wrote:
> On Tue, Mar 13, 2018 at 6:49 AM, Michal Hocko <mhocko@kernel.org> wrote:
> > On Wed 21-02-18 14:37:56, Shakeel Butt wrote:
> > [...]
> >> +#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;
> >> +}
> >
> > So you are relying that the caller will handle the reference counting
> > properly? I do not think this is a good idea.
> 
> For the fsnotify use-case, this assumption makes sense as fsnotify has
> an abstraction of fsnotify_group which is created by the
> person/process interested in the events and thus can be used to hold
> the reference to the person/process's memcg.

OK, but there is not any direct connection between fsnotify_group and
task_struct lifetimes, is it? This makes the API suspectible to
use-after-free bugs.

> Another use-case I have
> in mind is the filesystem mount. Basically attaching a mount with a
> memcg and thus all user pages and kmem allocations (inodes, dentries)
> for that mount will be charged to the attached memcg.

So you charge page cache to the origin task but metadata to a different
memcg?

> In this use-case
> the super_block is the perfect structure to hold the reference to the
> memcg.
> 
> If in future we find a use-case where this assumption does not make
> sense we can evolve the API and since this is kernel internal API, it
> should not be hard to evolve.
> 
> > Also do we need some kind
> > of debugging facility to detect unbalanced save/restore scopes?
> >
> 
> I am not sure, I didn't find other similar patterns (like PF_MEMALLOC)
> having debugging facility.

Maybe we need something more generic here.

> Maybe we can add such debugging facility
> when we find more users other than kmalloc & kmem_cache_alloc. Vmalloc
> may be one but I could not think of a use-case for vmalloc for remote
> charging, so, no need to add more code at this time.
> 
> > [...]
> >> @@ -2260,7 +2269,10 @@ 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);
> >> +     if (current->target_memcg)
> >> +             memcg = get_mem_cgroup(current->target_memcg);
> >> +     if (!memcg)
> >> +             memcg = get_mem_cgroup_from_mm(current->mm);
> >>       kmemcg_id = READ_ONCE(memcg->kmemcg_id);
> >>       if (kmemcg_id < 0)
> >>               goto out;
> >
> > You are also adding one branch for _each_ charge path even though the
> > usecase is rather limited.
> >
> 
> I understand the concern but the charging path, IMO, is much complex
> than just one or couple of additional branches. I can run a simple
> microbenchmark to see if there is anything noticeable here.

Charging path is still a _hot path_. Especially when the kmem accounting
is enabled by default. You cannot simply downplay the overhead. We have
_one_ user but all users should pay the price. This is simply hard to
justify. Maybe we can thing of something that would put the burden on
the charging context?
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations

[Shakeel Butt]

On Thu, Mar 15, 2018 at 10:49 AM, Michal Hocko <mhocko@kernel.org> wrote:
> On Tue 13-03-18 10:55:18, Shakeel Butt wrote:
>> On Tue, Mar 13, 2018 at 6:49 AM, Michal Hocko <mhocko@kernel.org> wrote:
>> > On Wed 21-02-18 14:37:56, Shakeel Butt wrote:
>> > [...]
>> >> +#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;
>> >> +}
>> >
>> > So you are relying that the caller will handle the reference counting
>> > properly? I do not think this is a good idea.
>>
>> For the fsnotify use-case, this assumption makes sense as fsnotify has
>> an abstraction of fsnotify_group which is created by the
>> person/process interested in the events and thus can be used to hold
>> the reference to the person/process's memcg.
>
> OK, but there is not any direct connection between fsnotify_group and
> task_struct lifetimes, is it? This makes the API suspectible to
> use-after-free bugs.
>

For fsnotify, whoever is calling [fanotify|inotify]_handle_event()
will have a stable reference to fsnotify_group and fsnotify_group has
reference to memcg. These allocations happen within
[fanotify|inotify]_handle_event(), so, for fsnotify I don't think
there will be use-after-free bugs.

Basically whoever is calling memcg variant of kmem_cache_alloc or
kmalloc should either have stable direct or indirect reference to the
memcg.

>> Another use-case I have
>> in mind is the filesystem mount. Basically attaching a mount with a
>> memcg and thus all user pages and kmem allocations (inodes, dentries)
>> for that mount will be charged to the attached memcg.
>
> So you charge page cache to the origin task but metadata to a different
> memcg?
>

No, both page cache and metadata to a different memcg.

>> In this use-case
>> the super_block is the perfect structure to hold the reference to the
>> memcg.
>>
>> If in future we find a use-case where this assumption does not make
>> sense we can evolve the API and since this is kernel internal API, it
>> should not be hard to evolve.
>>
>> > Also do we need some kind
>> > of debugging facility to detect unbalanced save/restore scopes?
>> >
>>
>> I am not sure, I didn't find other similar patterns (like PF_MEMALLOC)
>> having debugging facility.
>
> Maybe we need something more generic here.
>

Please do let me know if you have something in mind.

>> Maybe we can add such debugging facility
>> when we find more users other than kmalloc & kmem_cache_alloc. Vmalloc
>> may be one but I could not think of a use-case for vmalloc for remote
>> charging, so, no need to add more code at this time.
>>
>> > [...]
>> >> @@ -2260,7 +2269,10 @@ 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);
>> >> +     if (current->target_memcg)
>> >> +             memcg = get_mem_cgroup(current->target_memcg);
>> >> +     if (!memcg)
>> >> +             memcg = get_mem_cgroup_from_mm(current->mm);
>> >>       kmemcg_id = READ_ONCE(memcg->kmemcg_id);
>> >>       if (kmemcg_id < 0)
>> >>               goto out;
>> >
>> > You are also adding one branch for _each_ charge path even though the
>> > usecase is rather limited.
>> >
>>
>> I understand the concern but the charging path, IMO, is much complex
>> than just one or couple of additional branches. I can run a simple
>> microbenchmark to see if there is anything noticeable here.
>
> Charging path is still a _hot path_. Especially when the kmem accounting
> is enabled by default. You cannot simply downplay the overhead. We have
> _one_ user but all users should pay the price. This is simply hard to
> justify. Maybe we can thing of something that would put the burden on
> the charging context?
>

I will see if I can find out a way for that.

[PATCH] Re: [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations

[Shakeel Butt]

On Thu, Mar 15, 2018 at 10:49 AM, Michal Hocko <mhocko@kernel.org> wrote:
> Charging path is still a _hot path_. Especially when the kmem accounting
> is enabled by default. You cannot simply downplay the overhead. We have
> _one_ user but all users should pay the price. This is simply hard to
> justify. Maybe we can thing of something that would put the  burden on
> the charging context?

What do you think of the following?

Signed-off-by: Shakeel Butt <shakeelb@google.com>
---
 mm/memcontrol.c | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5d3ea8799a2c..205043283716 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -701,6 +701,20 @@ 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
@@ -2119,15 +2133,6 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
 }
 
 #ifndef CONFIG_SLOB
-static struct mem_cgroup *get_mem_cgroup(struct mem_cgroup *memcg)
-{
-	rcu_read_lock();
-	if (!css_tryget_online(&memcg->css))
-		memcg = NULL;
-	rcu_read_unlock();
-	return memcg;
-}
-
 static int memcg_alloc_cache_id(void)
 {
 	int id, size;
@@ -2257,7 +2262,7 @@ static inline bool memcg_kmem_bypass(void)
  */
 struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
 {
-	struct mem_cgroup *memcg = NULL;
+	struct mem_cgroup *memcg;
 	struct kmem_cache *memcg_cachep;
 	int kmemcg_id;
 
@@ -2269,10 +2274,7 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
 	if (current->memcg_kmem_skip_account)
 		return cachep;
 
-	if (current->target_memcg)
-		memcg = get_mem_cgroup(current->target_memcg);
-	if (!memcg)
-		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;
@@ -2350,16 +2352,13 @@ int memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
  */
 int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
 {
-	struct mem_cgroup *memcg = NULL;
+	struct mem_cgroup *memcg;
 	int ret = 0;
 
 	if (memcg_kmem_bypass())
 		return 0;
 
-	if (current->target_memcg)
-		memcg = get_mem_cgroup(current->target_memcg);
-	if (!memcg)
-		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