Following suggestion[1], offer a cgroupfs entry to allow an
administrator to request that a dmem controlled region also charges to
the memory controller.

Add mem_cgroup_dmem_charge/uncharge helpers to resolve the effective
cgroup from a dmem pool's cgroup, perform the charge and update a
MEMCG_DMEM stat counter.

Add a "dmem.memcg" control file at the root level to configure memcg
charging per region. The setting is disabled by default and locked on
first charge attempt.

[1] https://lore.kernel.org/all/a446b598-5041-450b-aaa9-3c39a09ff6a0@amd.com/

Signed-off-by: Eric Chanudet <echanude@redhat.com>
---
Changes in v2:
- Use mem_cgroup_dmem_{,un}charge to account for memcg pages instead of
  exposing raw nr_pages functions. Use it to centralize where to find
  the effective cgroup from the pool's cgroup (Johannes)
- Set depends_on for cgrp_memory if CONFIG_MEMCG by having a memory
  controller in children cgroup (Michal)
- Move dmem.memcg to the root level as it applies by region for all
  cgroups
- Add a dmem memory.stats entry for reporting memcg charges for dmem
  allocations.
- Wrap the memcg enable/disable/lock configuration under a single state
  to avoid toctou races and simplify transitions.
- Link to v1: https://lore.kernel.org/r/20260403-cgroup-dmem-memcg-double-charge-v1-0-c371d155de2a@redhat.com

---
Eric Chanudet (2):
      mm/memcontrol: add dmem charge/uncharge functions
      cgroup/dmem: add dmem.memcg control file for double-charging to memcg

 Documentation/admin-guide/cgroup-v2.rst |  23 +++++
 include/linux/memcontrol.h              |  16 ++++
 kernel/cgroup/dmem.c                    | 158 +++++++++++++++++++++++++++++++-
 mm/memcontrol.c                         |  65 +++++++++++++
 4 files changed, 259 insertions(+), 3 deletions(-)
---
base-commit: d989f135f71699294bb2ffd4726b526456e2db68
change-id: 20260327-cgroup-dmem-memcg-double-charge-0f100a9ffbf2

Best regards,
-- 
Eric Chanudet <echanude@redhat.com>