[1/2] fs: fsnotify: account fsnotify metadata to kmemcg
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Message ID 20180625230659.139822-2-shakeelb@google.com
State New
Headers show

Commit Message

Shakeel Butt June 25, 2018, 11:06 p.m. UTC
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.

However the listener can be in a different memcg than the memcg of the
producer and these allocations happen in the context of the event
producer. This patch introduces remote memcg charging scope API which the
producer can use to charge the allocations 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>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
---
Changelog since v6:
- Removed Jan's ACK as the code has changed a lot
- Squashed the separate remote charging API path into this one
- Removed kmalloc* & kmem_cache_alloc* APIs and only kept the scope API
- Changed fsnotify remote charging code to use scope API

Changelog since v5:
- None

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        | 17 ++++++++++--
 fs/notify/fanotify/fanotify_user.c   |  5 +++-
 fs/notify/group.c                    |  4 +++
 fs/notify/inotify/inotify_fsnotify.c | 15 +++++++++-
 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             | 41 ++++++++++++++++++++++++++++
 kernel/fork.c                        |  3 ++
 mm/memcontrol.c                      | 38 +++++++++++++++++++++++---
 12 files changed, 139 insertions(+), 16 deletions(-)

Comments

Amir Goldstein June 26, 2018, 5:49 a.m. UTC | #1
On Tue, Jun 26, 2018 at 2:06 AM, Shakeel Butt <shakeelb@google.com> wrote:
> 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.
>
> However the listener can be in a different memcg than the memcg of the
> producer and these allocations happen in the context of the event
> producer. This patch introduces remote memcg charging scope API which the
> producer can use to charge the allocations 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>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Amir Goldstein <amir73il@gmail.com>
> Cc: Greg Thelen <gthelen@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Roman Gushchin <guro@fb.com>
> ---
> Changelog since v6:
> - Removed Jan's ACK as the code has changed a lot
> - Squashed the separate remote charging API path into this one
> - Removed kmalloc* & kmem_cache_alloc* APIs and only kept the scope API
> - Changed fsnotify remote charging code to use scope API
>
> Changelog since v5:
> - None
>
> 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        | 17 ++++++++++--
>  fs/notify/fanotify/fanotify_user.c   |  5 +++-
>  fs/notify/group.c                    |  4 +++
>  fs/notify/inotify/inotify_fsnotify.c | 15 +++++++++-
>  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             | 41 ++++++++++++++++++++++++++++
>  kernel/fork.c                        |  3 ++
>  mm/memcontrol.c                      | 38 +++++++++++++++++++++++---
>  12 files changed, 139 insertions(+), 16 deletions(-)
>
> diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
> index e2bea2ac5dfb..a6365e6bc047 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 f90842efea13..d6dfcf0ec21f 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -11,6 +11,7 @@
>  #include <linux/types.h>
>  #include <linux/wait.h>
>  #include <linux/audit.h>
> +#include <linux/sched/mm.h>
>
>  #include "fanotify.h"
>
> @@ -140,8 +141,9 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
>                                                  struct inode *inode, u32 mask,
>                                                  const struct path *path)
>  {
> -       struct fanotify_event_info *event;
> +       struct fanotify_event_info *event = NULL;
>         gfp_t gfp = GFP_KERNEL;
> +       struct mem_cgroup *old_memcg = NULL;
>
>         /*
>          * For queues with unlimited length lost events are not expected and
> @@ -151,19 +153,25 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
>         if (group->max_events == UINT_MAX)
>                 gfp |= __GFP_NOFAIL;
>
> +       /* Whoever is interested in the event, pays for the allocation. */
> +       if (group->memcg) {
> +               gfp |= __GFP_ACCOUNT;
> +               old_memcg = memalloc_use_memcg(group->memcg);
> +       }
> +
>         if (fanotify_is_perm_event(mask)) {
>                 struct fanotify_perm_event_info *pevent;
>
>                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
>                 if (!pevent)
> -                       return NULL;
> +                       goto out;
>                 event = &pevent->fae;
>                 pevent->response = 0;
>                 goto init;
>         }
>         event = kmem_cache_alloc(fanotify_event_cachep, gfp);
>         if (!event)
> -               return NULL;
> +               goto out;
>  init: __maybe_unused
>         fsnotify_init_event(&event->fse, inode, mask);
>         event->tgid = get_pid(task_tgid(current));
> @@ -174,6 +182,9 @@ init: __maybe_unused
>                 event->path.mnt = NULL;
>                 event->path.dentry = NULL;
>         }
> +out:
> +       if (group->memcg)
> +               memalloc_unuse_memcg(old_memcg);
>         return event;
>  }
>
> 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 aa5468f23e45..cbcda1cb9a74 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 9ab6dde38a14..73b4d6c55497 100644
> --- a/fs/notify/inotify/inotify_fsnotify.c
> +++ b/fs/notify/inotify/inotify_fsnotify.c
> @@ -31,6 +31,7 @@
>  #include <linux/types.h>
>  #include <linux/sched.h>
>  #include <linux/sched/user.h>
> +#include <linux/sched/mm.h>
>
>  #include "inotify.h"
>
> @@ -73,9 +74,11 @@ int inotify_handle_event(struct fsnotify_group *group,
>         struct inotify_inode_mark *i_mark;
>         struct inotify_event_info *event;
>         struct fsnotify_event *fsn_event;
> +       struct mem_cgroup *old_memcg = NULL;
>         int ret;
>         int len = 0;
>         int alloc_len = sizeof(struct inotify_event_info);
> +       gfp_t gfp = GFP_KERNEL;
>
>         if (WARN_ON(fsnotify_iter_vfsmount_mark(iter_info)))
>                 return 0;
> @@ -98,7 +101,17 @@ 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);
> +       /* Whoever is interested in the event, pays for the allocation. */
> +       if (group->memcg) {
> +               gfp |= __GFP_ACCOUNT;
> +               old_memcg = memalloc_use_memcg(group->memcg);
> +       }
> +
> +       event = kmalloc(alloc_len, gfp);
> +
> +       if (group->memcg)
> +               memalloc_unuse_memcg(old_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 1cf5b779d862..749c46ababa0 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"
> @@ -636,6 +637,7 @@ 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);
> @@ -808,7 +810,8 @@ 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 b38964a7a521..a0c4790c5302 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.
> @@ -127,6 +129,8 @@ 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.
> @@ -137,8 +141,6 @@ 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 */
> @@ -160,6 +162,8 @@ 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 */
> @@ -167,8 +171,8 @@ 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 3607913032be..6c857be8a9b7 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -378,6 +378,8 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *, struct pglist_data *);
>  bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg);
>  struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
>
> +struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
> +
>  static inline
>  struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){
>         return css ? container_of(css, struct mem_cgroup, css) : NULL;
> @@ -857,6 +859,11 @@ 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/include/linux/sched.h b/include/linux/sched.h
> index 87bf02d93a27..9cba7f874443 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1149,6 +1149,9 @@ 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               *active_memcg;
>  #endif
>
>  #ifdef CONFIG_UPROBES
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 44d356f5e47c..75f2d6ee2b72 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -248,6 +248,47 @@ static inline void memalloc_noreclaim_restore(unsigned int flags)
>         current->flags = (current->flags & ~PF_MEMALLOC) | flags;
>  }
>
> +#ifdef CONFIG_MEMCG
> +/**
> + * memalloc_use_memcg - Starts the remote memcg charging scope.
> + * @memcg: memcg to charge.
> + *
> + * This function marks the beginning of the remote memcg charging scope. All the
> + * __GFP_ACCOUNT allocations till the end of the scope will be charged to the
> + * given memcg. Passing NULL will disable the remote memcg charging of the outer
> + * scope.
> + */
> +static inline struct mem_cgroup *memalloc_use_memcg(struct mem_cgroup *memcg)
> +{
> +       struct mem_cgroup *old_memcg = current->active_memcg;
> +
> +       current->active_memcg = memcg;
> +       return old_memcg;
> +}
> +
> +/**
> + * memalloc_unuse_memcg - Ends the remote memcg charging scope.
> + * @memcg: outer scope memcg to restore.
> + *
> + * This function marks the end of the remote memcg charging scope started by
> + * memalloc_use_memcg(). Always make sure the given memcg is the return valure
> + * from the pairing memalloc_use_memcg call.
> + */
> +static inline void memalloc_unuse_memcg(struct mem_cgroup *memcg)
> +{
> +       current->active_memcg = memcg;
> +}

The verb 'unuse' takes an argument memcg and 'uses' it - too weird.
You can use 'override'/'revert' verbs like override_creds or just call
memalloc_use_memcg(old_memcg) since there is no reference taken
anyway in use_memcg and no reference released in unuse_memcg.

Otherwise looks good to me.

Thanks,
Amir,
Shakeel Butt June 26, 2018, 6 p.m. UTC | #2
On Mon, Jun 25, 2018 at 10:49 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
...
>
> The verb 'unuse' takes an argument memcg and 'uses' it - too weird.
> You can use 'override'/'revert' verbs like override_creds or just call
> memalloc_use_memcg(old_memcg) since there is no reference taken
> anyway in use_memcg and no reference released in unuse_memcg.
>
> Otherwise looks good to me.
>

Thanks for your feedback. Just using memalloc_use_memcg(old_memcg) and
ignoring the return seems more simple. I will wait for feedback from
other before changing anything.

thanks,
Shakeel
Johannes Weiner June 26, 2018, 6:57 p.m. UTC | #3
On Tue, Jun 26, 2018 at 11:00:53AM -0700, Shakeel Butt wrote:
> On Mon, Jun 25, 2018 at 10:49 PM Amir Goldstein <amir73il@gmail.com> wrote:
> >
> ...
> >
> > The verb 'unuse' takes an argument memcg and 'uses' it - too weird.
> > You can use 'override'/'revert' verbs like override_creds or just call
> > memalloc_use_memcg(old_memcg) since there is no reference taken
> > anyway in use_memcg and no reference released in unuse_memcg.
> >
> > Otherwise looks good to me.
> >
> 
> Thanks for your feedback. Just using memalloc_use_memcg(old_memcg) and
> ignoring the return seems more simple. I will wait for feedback from
> other before changing anything.

We're not nesting calls to memalloc_use_memcg(), right? So we don't
have to return old_memcg and don't have to pass anything to unuse, it
can always set current->active_memcg to NULL.
Johannes Weiner June 26, 2018, 7:06 p.m. UTC | #4
On Mon, Jun 25, 2018 at 04:06:58PM -0700, Shakeel Butt wrote:
> @@ -140,8 +141,9 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
>  						 struct inode *inode, u32 mask,
>  						 const struct path *path)
>  {
> -	struct fanotify_event_info *event;
> +	struct fanotify_event_info *event = NULL;
>  	gfp_t gfp = GFP_KERNEL;
> +	struct mem_cgroup *old_memcg = NULL;
>  
>  	/*
>  	 * For queues with unlimited length lost events are not expected and
> @@ -151,19 +153,25 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
>  	if (group->max_events == UINT_MAX)
>  		gfp |= __GFP_NOFAIL;
>  
> +	/* Whoever is interested in the event, pays for the allocation. */
> +	if (group->memcg) {
> +		gfp |= __GFP_ACCOUNT;
> +		old_memcg = memalloc_use_memcg(group->memcg);
> +	}

group->memcg is only NULL when memcg is disabled or there is some
offlining race. Can you make memalloc_use_memcg(NULL) mean that it
should charge root_mem_cgroup instead of current->mm->memcg? That way
we can make this site unconditional while retaining the behavior:

	gfp_t gfp = GFP_KERNEL | __GFP_ACCOUNT;

	memalloc_use_memcg(group->memcg);
	kmem_cache_alloc(..., gfp);
out:
	memalloc_unuse_memcg();

(dropping old_memcg and the unuse parameter as per the other mail)

>  	if (fanotify_is_perm_event(mask)) {
>  		struct fanotify_perm_event_info *pevent;
>  
>  		pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
>  		if (!pevent)
> -			return NULL;
> +			goto out;
>  		event = &pevent->fae;
>  		pevent->response = 0;
>  		goto init;
>  	}
>  	event = kmem_cache_alloc(fanotify_event_cachep, gfp);
>  	if (!event)
> -		return NULL;
> +		goto out;
>  init: __maybe_unused
>  	fsnotify_init_event(&event->fse, inode, mask);
>  	event->tgid = get_pid(task_tgid(current));
> @@ -174,6 +182,9 @@ init: __maybe_unused
>  		event->path.mnt = NULL;
>  		event->path.dentry = NULL;
>  	}
> +out:
> +	if (group->memcg)
> +		memalloc_unuse_memcg(old_memcg);
>  	return event;
>  }

Thanks,
Johannes
Shakeel Butt June 26, 2018, 7:07 p.m. UTC | #5
On Tue, Jun 26, 2018 at 11:55 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> On Tue, Jun 26, 2018 at 11:00:53AM -0700, Shakeel Butt wrote:
> > On Mon, Jun 25, 2018 at 10:49 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > >
> > ...
> > >
> > > The verb 'unuse' takes an argument memcg and 'uses' it - too weird.
> > > You can use 'override'/'revert' verbs like override_creds or just call
> > > memalloc_use_memcg(old_memcg) since there is no reference taken
> > > anyway in use_memcg and no reference released in unuse_memcg.
> > >
> > > Otherwise looks good to me.
> > >
> >
> > Thanks for your feedback. Just using memalloc_use_memcg(old_memcg) and
> > ignoring the return seems more simple. I will wait for feedback from
> > other before changing anything.
>
> We're not nesting calls to memalloc_use_memcg(), right? So we don't
> have to return old_memcg and don't have to pass anything to unuse, it
> can always set current->active_memcg to NULL.

For buffer_head, the allocation is done with GFP_NOFS. So, I think
there is no chance of nesting. The fsnotify uses GFP_KERNEL but based
on my limited understanding of fsnotify, there should not be any
nesting i.e. the allocation triggering reclaim which trigger fsnotify
events. Though I would like Amir or Jan to confirm there is no nesting
possible.

thanks,
Shakeel
Shakeel Butt June 26, 2018, 8:05 p.m. UTC | #6
On Tue, Jun 26, 2018 at 12:03 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> On Mon, Jun 25, 2018 at 04:06:58PM -0700, Shakeel Butt wrote:
> > @@ -140,8 +141,9 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
> >                                                struct inode *inode, u32 mask,
> >                                                const struct path *path)
> >  {
> > -     struct fanotify_event_info *event;
> > +     struct fanotify_event_info *event = NULL;
> >       gfp_t gfp = GFP_KERNEL;
> > +     struct mem_cgroup *old_memcg = NULL;
> >
> >       /*
> >        * For queues with unlimited length lost events are not expected and
> > @@ -151,19 +153,25 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
> >       if (group->max_events == UINT_MAX)
> >               gfp |= __GFP_NOFAIL;
> >
> > +     /* Whoever is interested in the event, pays for the allocation. */
> > +     if (group->memcg) {
> > +             gfp |= __GFP_ACCOUNT;
> > +             old_memcg = memalloc_use_memcg(group->memcg);
> > +     }
>
> group->memcg is only NULL when memcg is disabled or there is some
> offlining race. Can you make memalloc_use_memcg(NULL) mean that it
> should charge root_mem_cgroup instead of current->mm->memcg? That way
> we can make this site unconditional while retaining the behavior:
>
>         gfp_t gfp = GFP_KERNEL | __GFP_ACCOUNT;
>
>         memalloc_use_memcg(group->memcg);
>         kmem_cache_alloc(..., gfp);
> out:
>         memalloc_unuse_memcg();
>
> (dropping old_memcg and the unuse parameter as per the other mail)
>

group->memcg is only NULL when memcg is disabled (i.e.
get_mem_cgroup_from_mm() returns root_mem_cgroup for offlined
mm->memcg). Though group->memcg can point to an offlined memcg.

If I understand you correctly this is what we want:

1. If group->memcg is NULL then __GFP_ACCOUNT is a noop i.e. memcg is disabled.
2. If group->memcg is root_mem_cgroup, then __GFP_ACCOUNT again is a
kind of noop (charges to root_mem_cgroups are bypassed).
3. If group->memcg is offlined memcg, then make __GFP_ACCOUNT noop by
returning root_mem_cgroup from get_mem_cgroup_from_current().
4. Else charge group->memcg.

This seems reasonable. After your Ack and Amir's or Jan's answer to
the nesting query, I will resend the next version of this patch
series.

In future if we find any use-cases of memalloc_use_memcg nesting then
we can make it work for nesting.

thanks,
Shakeel
Amir Goldstein June 27, 2018, 5:50 a.m. UTC | #7
On Tue, Jun 26, 2018 at 11:05 PM, Shakeel Butt <shakeelb@google.com> wrote:
> On Tue, Jun 26, 2018 at 12:03 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>>
>> On Mon, Jun 25, 2018 at 04:06:58PM -0700, Shakeel Butt wrote:
>> > @@ -140,8 +141,9 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
>> >                                                struct inode *inode, u32 mask,
>> >                                                const struct path *path)
>> >  {
>> > -     struct fanotify_event_info *event;
>> > +     struct fanotify_event_info *event = NULL;
>> >       gfp_t gfp = GFP_KERNEL;
>> > +     struct mem_cgroup *old_memcg = NULL;
>> >
>> >       /*
>> >        * For queues with unlimited length lost events are not expected and
>> > @@ -151,19 +153,25 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
>> >       if (group->max_events == UINT_MAX)
>> >               gfp |= __GFP_NOFAIL;
>> >
>> > +     /* Whoever is interested in the event, pays for the allocation. */
>> > +     if (group->memcg) {
>> > +             gfp |= __GFP_ACCOUNT;
>> > +             old_memcg = memalloc_use_memcg(group->memcg);
>> > +     }
>>
>> group->memcg is only NULL when memcg is disabled or there is some
>> offlining race. Can you make memalloc_use_memcg(NULL) mean that it
>> should charge root_mem_cgroup instead of current->mm->memcg? That way
>> we can make this site unconditional while retaining the behavior:
>>
>>         gfp_t gfp = GFP_KERNEL | __GFP_ACCOUNT;
>>
>>         memalloc_use_memcg(group->memcg);
>>         kmem_cache_alloc(..., gfp);
>> out:
>>         memalloc_unuse_memcg();
>>
>> (dropping old_memcg and the unuse parameter as per the other mail)
>>
>
> group->memcg is only NULL when memcg is disabled (i.e.
> get_mem_cgroup_from_mm() returns root_mem_cgroup for offlined
> mm->memcg). Though group->memcg can point to an offlined memcg.
>
> If I understand you correctly this is what we want:
>
> 1. If group->memcg is NULL then __GFP_ACCOUNT is a noop i.e. memcg is disabled.
> 2. If group->memcg is root_mem_cgroup, then __GFP_ACCOUNT again is a
> kind of noop (charges to root_mem_cgroups are bypassed).
> 3. If group->memcg is offlined memcg, then make __GFP_ACCOUNT noop by
> returning root_mem_cgroup from get_mem_cgroup_from_current().
> 4. Else charge group->memcg.
>
> This seems reasonable. After your Ack and Amir's or Jan's answer to
> the nesting query, I will resend the next version of this patch
> series.
>
> In future if we find any use-cases of memalloc_use_memcg nesting then
> we can make it work for nesting.
>

For the fsnotify use case memalloc_use_memcg() certainly doesn't
need to nest, but I wonder, if that facility becomes popular among different
subsystems, how exactly do you intend to monitor that it doesn't grow
nested use cases? I would suggest that you at least leave a
WARN_ON_ONCE if memalloc_use_memcg() is called and
active_memcg is already set.

Thanks,
Amir.
Jan Kara June 27, 2018, 7:31 a.m. UTC | #8
On Tue 26-06-18 12:07:57, Shakeel Butt wrote:
> On Tue, Jun 26, 2018 at 11:55 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
> >
> > On Tue, Jun 26, 2018 at 11:00:53AM -0700, Shakeel Butt wrote:
> > > On Mon, Jun 25, 2018 at 10:49 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > > >
> > > ...
> > > >
> > > > The verb 'unuse' takes an argument memcg and 'uses' it - too weird.
> > > > You can use 'override'/'revert' verbs like override_creds or just call
> > > > memalloc_use_memcg(old_memcg) since there is no reference taken
> > > > anyway in use_memcg and no reference released in unuse_memcg.
> > > >
> > > > Otherwise looks good to me.
> > > >
> > >
> > > Thanks for your feedback. Just using memalloc_use_memcg(old_memcg) and
> > > ignoring the return seems more simple. I will wait for feedback from
> > > other before changing anything.
> >
> > We're not nesting calls to memalloc_use_memcg(), right? So we don't
> > have to return old_memcg and don't have to pass anything to unuse, it
> > can always set current->active_memcg to NULL.
> 
> For buffer_head, the allocation is done with GFP_NOFS. So, I think
> there is no chance of nesting. The fsnotify uses GFP_KERNEL but based
> on my limited understanding of fsnotify, there should not be any
> nesting i.e. the allocation triggering reclaim which trigger fsnotify
> events. Though I would like Amir or Jan to confirm there is no nesting
> possible.

You are correct. Fsnotify events are generated only as a result of some
syscall, not due to reclaim or stuff like that.

								Honza

Patch
diff mbox

diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
index e2bea2ac5dfb..a6365e6bc047 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 f90842efea13..d6dfcf0ec21f 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -11,6 +11,7 @@ 
 #include <linux/types.h>
 #include <linux/wait.h>
 #include <linux/audit.h>
+#include <linux/sched/mm.h>
 
 #include "fanotify.h"
 
@@ -140,8 +141,9 @@  struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
 						 struct inode *inode, u32 mask,
 						 const struct path *path)
 {
-	struct fanotify_event_info *event;
+	struct fanotify_event_info *event = NULL;
 	gfp_t gfp = GFP_KERNEL;
+	struct mem_cgroup *old_memcg = NULL;
 
 	/*
 	 * For queues with unlimited length lost events are not expected and
@@ -151,19 +153,25 @@  struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
 	if (group->max_events == UINT_MAX)
 		gfp |= __GFP_NOFAIL;
 
+	/* Whoever is interested in the event, pays for the allocation. */
+	if (group->memcg) {
+		gfp |= __GFP_ACCOUNT;
+		old_memcg = memalloc_use_memcg(group->memcg);
+	}
+
 	if (fanotify_is_perm_event(mask)) {
 		struct fanotify_perm_event_info *pevent;
 
 		pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
 		if (!pevent)
-			return NULL;
+			goto out;
 		event = &pevent->fae;
 		pevent->response = 0;
 		goto init;
 	}
 	event = kmem_cache_alloc(fanotify_event_cachep, gfp);
 	if (!event)
-		return NULL;
+		goto out;
 init: __maybe_unused
 	fsnotify_init_event(&event->fse, inode, mask);
 	event->tgid = get_pid(task_tgid(current));
@@ -174,6 +182,9 @@  init: __maybe_unused
 		event->path.mnt = NULL;
 		event->path.dentry = NULL;
 	}
+out:
+	if (group->memcg)
+		memalloc_unuse_memcg(old_memcg);
 	return event;
 }
 
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 aa5468f23e45..cbcda1cb9a74 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 9ab6dde38a14..73b4d6c55497 100644
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -31,6 +31,7 @@ 
 #include <linux/types.h>
 #include <linux/sched.h>
 #include <linux/sched/user.h>
+#include <linux/sched/mm.h>
 
 #include "inotify.h"
 
@@ -73,9 +74,11 @@  int inotify_handle_event(struct fsnotify_group *group,
 	struct inotify_inode_mark *i_mark;
 	struct inotify_event_info *event;
 	struct fsnotify_event *fsn_event;
+	struct mem_cgroup *old_memcg = NULL;
 	int ret;
 	int len = 0;
 	int alloc_len = sizeof(struct inotify_event_info);
+	gfp_t gfp = GFP_KERNEL;
 
 	if (WARN_ON(fsnotify_iter_vfsmount_mark(iter_info)))
 		return 0;
@@ -98,7 +101,17 @@  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);
+	/* Whoever is interested in the event, pays for the allocation. */
+	if (group->memcg) {
+		gfp |= __GFP_ACCOUNT;
+		old_memcg = memalloc_use_memcg(group->memcg);
+	}
+
+	event = kmalloc(alloc_len, gfp);
+
+	if (group->memcg)
+		memalloc_unuse_memcg(old_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 1cf5b779d862..749c46ababa0 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"
@@ -636,6 +637,7 @@  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);
@@ -808,7 +810,8 @@  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 b38964a7a521..a0c4790c5302 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.
@@ -127,6 +129,8 @@  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.
@@ -137,8 +141,6 @@  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 */
@@ -160,6 +162,8 @@  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 */
@@ -167,8 +171,8 @@  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 3607913032be..6c857be8a9b7 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -378,6 +378,8 @@  struct lruvec *mem_cgroup_page_lruvec(struct page *, struct pglist_data *);
 bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg);
 struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 
+struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
+
 static inline
 struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){
 	return css ? container_of(css, struct mem_cgroup, css) : NULL;
@@ -857,6 +859,11 @@  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/include/linux/sched.h b/include/linux/sched.h
index 87bf02d93a27..9cba7f874443 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1149,6 +1149,9 @@  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		*active_memcg;
 #endif
 
 #ifdef CONFIG_UPROBES
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 44d356f5e47c..75f2d6ee2b72 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -248,6 +248,47 @@  static inline void memalloc_noreclaim_restore(unsigned int flags)
 	current->flags = (current->flags & ~PF_MEMALLOC) | flags;
 }
 
+#ifdef CONFIG_MEMCG
+/**
+ * memalloc_use_memcg - Starts the remote memcg charging scope.
+ * @memcg: memcg to charge.
+ *
+ * This function marks the beginning of the remote memcg charging scope. All the
+ * __GFP_ACCOUNT allocations till the end of the scope will be charged to the
+ * given memcg. Passing NULL will disable the remote memcg charging of the outer
+ * scope.
+ */
+static inline struct mem_cgroup *memalloc_use_memcg(struct mem_cgroup *memcg)
+{
+	struct mem_cgroup *old_memcg = current->active_memcg;
+
+	current->active_memcg = memcg;
+	return old_memcg;
+}
+
+/**
+ * memalloc_unuse_memcg - Ends the remote memcg charging scope.
+ * @memcg: outer scope memcg to restore.
+ *
+ * This function marks the end of the remote memcg charging scope started by
+ * memalloc_use_memcg(). Always make sure the given memcg is the return valure
+ * from the pairing memalloc_use_memcg call.
+ */
+static inline void memalloc_unuse_memcg(struct mem_cgroup *memcg)
+{
+	current->active_memcg = memcg;
+}
+#else
+static inline struct mem_cgroup *memalloc_use_memcg(struct mem_cgroup *memcg)
+{
+	return NULL;
+}
+
+static inline void memalloc_unuse_memcg(struct mem_cgroup *memcg)
+{
+}
+#endif
+
 #ifdef CONFIG_MEMBARRIER
 enum {
 	MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY		= (1U << 0),
diff --git a/kernel/fork.c b/kernel/fork.c
index a64d0a19f174..0b07db6fef06 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -843,6 +843,9 @@  static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	tsk->fail_nth = 0;
 #endif
 
+#ifdef CONFIG_MEMCG
+	tsk->active_memcg = NULL;
+#endif
 	return tsk;
 
 free_stack:
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 02e77c88967a..6b1a8f8e0a82 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -678,9 +678,20 @@  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)
+/**
+ * get_mem_cgroup_from_mm: Obtain a reference on given mm_struct's memcg.
+ * @mm: mm from which memcg should be extracted. It can be NULL.
+ *
+ * Obtain a reference on mm->memcg and returns it if successful. Otherwise
+ * root_mem_cgroup is returned. However if mem_cgroup is disabled, NULL is
+ * returned.
+ */
+struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 {
-	struct mem_cgroup *memcg = NULL;
+	struct mem_cgroup *memcg;
+
+	if (mem_cgroup_disabled())
+		return NULL;
 
 	rcu_read_lock();
 	do {
@@ -700,6 +711,25 @@  static struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 	rcu_read_unlock();
 	return memcg;
 }
+EXPORT_SYMBOL(get_mem_cgroup_from_mm);
+
+/**
+ * First try to obtain reference on current->active_memcg. On failure, try to
+ * obtain reference on current->mm->memcg. On further failure root_mem_cgroup
+ * is returned.
+ */
+static __always_inline struct mem_cgroup *get_mem_cgroup_from_current(void)
+{
+	if (unlikely(current->active_memcg)) {
+		rcu_read_lock();
+		if (css_tryget_online(&current->active_memcg->css)) {
+			rcu_read_unlock();
+			return current->active_memcg;
+		}
+		rcu_read_unlock();
+	}
+	return get_mem_cgroup_from_mm(current->mm);
+}
 
 /**
  * mem_cgroup_iter - iterate over memory cgroup hierarchy
@@ -2260,7 +2290,7 @@  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_from_current();
 	kmemcg_id = READ_ONCE(memcg->kmemcg_id);
 	if (kmemcg_id < 0)
 		goto out;
@@ -2344,7 +2374,7 @@  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_from_current();
 	if (!mem_cgroup_is_root(memcg)) {
 		ret = memcg_kmem_charge_memcg(page, gfp, order, memcg);
 		if (!ret)