[PATCH v2 00/14] mm: memcg: separate legacy cgroup v1 code and put under config option

[Roman Gushchin <roman.gushchin@linux.dev>]

Cgroups v2 have been around for a while and many users have fully adopted them,
so they never use cgroups v1 features and functionality. Yet they have to "pay"
for the cgroup v1 support anyway:
1) the kernel binary contains an unused cgroup v1 code,
2) some code paths have additional checks which are not needed,
3) some common structures like task_struct and mem_cgroup contain unused
   cgroup v1-specific members.

Cgroup v1's memory controller has a number of features that are not supported
by cgroup v2 and their implementation is pretty much self contained.
Most notably, these features are: soft limit reclaim, oom handling in userspace,
complicated event notification system, charge migration. Cgroup v1-specific code
in memcontrol.c is close to 4k lines in size and it's intervened with generic
and cgroup v2-specific code. It's a burden on developers and maintainers.

This patchset aims to solve these problems by:
1) moving cgroup v1-specific memcg code to the new mm/memcontrol-v1.c file,
2) putting definitions shared by memcontrol.c and memcontrol-v1.c into the
   mm/memcontrol-v1.h header,
3) introducing the CONFIG_MEMCG_V1 config option, turned off by default,
4) making memcontrol-v1.c to compile only if CONFIG_MEMCG_V1 is set.

If CONFIG_MEMCG_V1 is not set, cgroup v1 memory controller is still available
for mounting, however no memory-specific control knobs are present.

This patchset is based against mm-unstable tree (b610f75d19a34),
however a version based on mm-stable can be found here:
  https://github.com/rgushchin/linux/tree/memcontrol_v1.1-stable .

v2:
  - minor compilation fix
  - #else/#endif comments fix (Lance Yang)

v1:
  - switched to CONFIG_MEMCG_V1 being off by default based on LSFMMBPF
    discussion [1]
  - switched to memcg1_ prefix (Johannes)
  - many minor fixes
  - dropped patches which put struct memcg members under CONFIG_MEMCG_V1
    (will post as a separate patchset)

rfc:
  https://lwn.net/Articles/973082/

[1]: https://lwn.net/Articles/974575/

MAINTAINERS                |    2 +
include/linux/memcontrol.h |  156 ++++---
init/Kconfig               |    9 +
mm/Makefile                |    2 +
mm/memcontrol-v1.c         | 2933 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
mm/memcontrol-v1.h         |  132 ++++++
mm/memcontrol.c            | 4169 +++++++++++++++++++++++++++---------------------------------------------------------------------------------------------------------------------------------------------------
mm/vmscan.c                |   10 +-
8 files changed, 3794 insertions(+), 3619 deletions(-)

Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>


Roman Gushchin (14):
  mm: memcg: introduce memcontrol-v1.c
  mm: memcg: move soft limit reclaim code to memcontrol-v1.c
  mm: memcg: rename soft limit reclaim-related functions
  mm: memcg: move charge migration code to memcontrol-v1.c
  mm: memcg: rename charge move-related functions
  mm: memcg: move legacy memcg event code into memcontrol-v1.c
  mm: memcg: rename memcg_check_events()
  mm: memcg: move cgroup v1 oom handling code into memcontrol-v1.c
  mm: memcg: rename memcg_oom_recover()
  mm: memcg: move cgroup v1 interface files to memcontrol-v1.c
  mm: memcg: make memcg1_update_tree() static
  mm: memcg: group cgroup v1 memcg related declarations
  mm: memcg: put cgroup v1-related members of task_struct under config
    option
  MAINTAINERS: add mm/memcontrol-v1.c/h to the list of maintained files

 MAINTAINERS                |    2 +
 include/linux/memcontrol.h |  156 +-
 init/Kconfig               |    9 +
 mm/Makefile                |    2 +
 mm/memcontrol-v1.c         | 2933 +++++++++++++++++++++++++
 mm/memcontrol-v1.h         |  132 ++
 mm/memcontrol.c            | 4141 ++++++------------------------------
 mm/vmscan.c                |   10 +-
 8 files changed, 3780 insertions(+), 3605 deletions(-)
 create mode 100644 mm/memcontrol-v1.c
 create mode 100644 mm/memcontrol-v1.h

-- 
2.45.2