[PATCH 0/5] Use obj_cgroup APIs to change kmem pages

[Muchun Song]

Since Roman series "The new cgroup slab memory controller" applied. All
slab objects are changed via the new APIs of obj_cgroup. This new APIs
introduce a struct obj_cgroup instead of using struct mem_cgroup directly
to charge slab objects. It prevents long-living objects from pinning the
original memory cgroup in the memory. But there are still some corner
objects (e.g. allocations larger than order-1 page on SLUB) which are
not charged via the API of obj_cgroup. Those objects (include the pages
which are allocated from buddy allocator directly) are charged as kmem
pages which still hold a reference to the memory cgroup.

E.g. We know that the kernel stack is charged as kmem pages because the
size of the kernel stack can be greater than 2 pages (e.g. 16KB on x86_64
or arm64). If we create a thread (suppose the thread stack is charged to
memory cgroup A) and then move it from memory cgroup A to memory cgroup
B. Because the kernel stack of the thread hold a reference to the memory
cgroup A. The thread can pin the memory cgroup A in the memory even if
we remove the cgroup A. If we want to see this scenario by using the
following script. We can see that the system has added 500 dying cgroups.

	#!/bin/bash

	cat /proc/cgroups | grep memory

	cd /sys/fs/cgroup/memory
	echo 1 > memory.move_charge_at_immigrate

	for i in range{1..500}
	do
		mkdir kmem_test
		echo $$ > kmem_test/cgroup.procs
		sleep 3600 &
		echo $$ > cgroup.procs
		echo `cat kmem_test/cgroup.procs` > cgroup.procs
		rmdir kmem_test
	done

	cat /proc/cgroups | grep memory

This patchset aims to make those kmem pages drop the reference to memory
cgroup by using the APIs of obj_cgroup. Finally, we can see that the number
of the dying cgroups will not increase if we run the above test script.

Patch 1-3 are using obj_cgroup APIs to charge kmem pages. The remote
memory cgroup charing APIs is a mechanism to charge kernel memory to a
given memory cgroup. So I also make it use the APIs of obj_cgroup.
Patch 4-5 are doing this.

Muchun Song (5):
  mm: memcontrol: introduce obj_cgroup_{un}charge_page
  mm: memcontrol: make page_memcg{_rcu} only applicable for non-kmem
    page
  mm: memcontrol: reparent the kmem pages on cgroup removal
  mm: memcontrol: move remote memcg charging APIs to CONFIG_MEMCG_KMEM
  mm: memcontrol: use object cgroup for remote memory cgroup charging

 fs/buffer.c                          |  10 +-
 fs/notify/fanotify/fanotify.c        |   6 +-
 fs/notify/fanotify/fanotify_user.c   |   2 +-
 fs/notify/group.c                    |   3 +-
 fs/notify/inotify/inotify_fsnotify.c |   8 +-
 fs/notify/inotify/inotify_user.c     |   2 +-
 include/linux/bpf.h                  |   2 +-
 include/linux/fsnotify_backend.h     |   2 +-
 include/linux/memcontrol.h           | 109 +++++++++++---
 include/linux/sched.h                |   6 +-
 include/linux/sched/mm.h             |  30 ++--
 kernel/bpf/syscall.c                 |  35 ++---
 kernel/fork.c                        |   4 +-
 mm/memcontrol.c                      | 276 ++++++++++++++++++++++-------------
 mm/page_alloc.c                      |   4 +-
 15 files changed, 324 insertions(+), 175 deletions(-)

-- 
2.11.0