Re: [PATCH 1/7] kernel/cgroup: Add "dev" memory accounting cgroup

[Waiman Long <llong@redhat.com>]

On 10/23/24 3:52 AM, Maarten Lankhorst wrote:
> The initial version was based roughly on the rdma and misc cgroup
> controllers, with a lot of the accounting code borrowed from rdma.
>
> The current version is a complete rewrite with page counter; it uses
> the same min/low/max semantics as the memory cgroup as a result.
>
> There's a small mismatch as TTM uses u64, and page_counter long pages.
> In practice it's not a problem. 32-bits systems don't really come with
>> =4GB cards and as long as we're consistently wrong with units, it's
> fine. The device page size may not be in the same units as kernel page
> size, and each region might also have a different page size (VRAM vs GART
> for example).
>
> The interface is simple:
> - populate dev_cgroup_try_charge->regions[..] name and size for each active
>    region, set num_regions accordingly.
> - Call (dev,drmm)_cgroup_register_device()
> - Use dev_cgroup_try_charge to check if you can allocate a chunk of memory,
>    use dev_cgroup__uncharge when freeing it. This may return an error code,
>    or -EAGAIN when the cgroup limit is reached. In that case a reference
>    to the limiting pool is returned.
> - The limiting cs can be used as compare function for
>    dev_cgroup_state_evict_valuable.
> - After having evicted enough, drop reference to limiting cs with
>    dev_cgroup_pool_state_put.
>
> This API allows you to limit device resources with cgroups.
> You can see the supported cards in /sys/fs/cgroup/dev.region.capacity
> You need to echo +dev to cgroup.subtree_control, and then you can
> partition memory.
>
> Co-developed-by: Friedrich Vock <friedrich.vock@gmx.de>
> Signed-off-by: Friedrich Vock <friedrich.vock@gmx.de>
> Co-developed-by: Maxime Ripard <mripard@kernel.org>
> Signed-off-by: Maxime Ripard <mripard@kernel.org>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>   Documentation/admin-guide/cgroup-v2.rst |  51 ++
>   Documentation/core-api/cgroup.rst       |   9 +
>   Documentation/core-api/index.rst        |   1 +
>   Documentation/gpu/drm-compute.rst       |  54 ++
>   include/linux/cgroup_dev.h              |  91 +++
>   include/linux/cgroup_subsys.h           |   4 +
>   include/linux/page_counter.h            |   2 +-
>   init/Kconfig                            |   7 +
>   kernel/cgroup/Makefile                  |   1 +
>   kernel/cgroup/dev.c                     | 893 ++++++++++++++++++++++++
>   mm/page_counter.c                       |   4 +-
>   11 files changed, 1114 insertions(+), 3 deletions(-)
>   create mode 100644 Documentation/core-api/cgroup.rst
>   create mode 100644 Documentation/gpu/drm-compute.rst
>   create mode 100644 include/linux/cgroup_dev.h
>   create mode 100644 kernel/cgroup/dev.c

Just a general comment.

Cgroup v1 has a legacy device controller in security/device_cgroup.c 
which is no longer available in cgroup v2. So if you use the name device 
controller, the documentation must be clear that it is completely 
different and have no relationship from the device controller in cgroup v1.

Cheers,
Longman