[v1,0/3] mm: memcg: deprecate cgroup v1 non-hierarchical mode

Message

Roman Gushchin Nov. 10, 2020, 10:07 p.m. UTC

The non-hierarchical cgroup v1 mode is a legacy of early days
of the memory controller and doesn't bring any value today.
However, it complicates the code and creates many edge cases
all over the memory controller code.

It's a good time to deprecate it completely. This patchset removes
the internal logic, adjusts the user interface and updates
the documentation. The alt patch removes some bits of the cgroup
core code, which become obsolete.

From Michal Hocko:
All that we know today is that we have a warning in place to complain
loudly when somebody relies on use_hierarchy=0 with a deeper
hierarchy. For all those years we have seen _zero_ reports that would
describe a sensible usecase.
Moreover we (SUSE) have backported this warning into old distribution
kernels (since 3.0 based kernels) to extend the coverage and didn't hear
even for users who adopt new kernels only very slowly. The only report
we have seen so far was a LTP test suite which doesn't really reflect
any real life usecase.

v1:
  - added a note from Michal
  - added acks and reviews

rfc:
  - https://lwn.net/Articles/835983/


Roman Gushchin (3):
  mm: memcg: deprecate the non-hierarchical mode
  docs: cgroup-v1: reflect the deprecation of the non-hierarchical mode
  cgroup: remove obsoleted broken_hierarchy and warned_broken_hierarchy

 .../admin-guide/cgroup-v1/memcg_test.rst      |  8 +-
 .../admin-guide/cgroup-v1/memory.rst          | 40 +++------
 include/linux/cgroup-defs.h                   | 15 ----
 include/linux/memcontrol.h                    |  7 --
 kernel/cgroup/cgroup.c                        | 12 ---
 mm/memcontrol.c                               | 90 +++----------------
 6 files changed, 29 insertions(+), 143 deletions(-)