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

[Shakeel Butt <shakeel.butt@linux.dev>]

On Mon, Jun 24, 2024 at 05:58:52PM GMT, Roman Gushchin wrote:
> 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>

For the series:

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>