[RFC PATCH v2 1/6] mm, doc: Add doc for MPOL_F_NUMA_BALANCING

[Huang, Ying]

Yafang Shao <laoar.shao at gmail.com> writes:

> The document on MPOL_F_NUMA_BALANCING was missed in the initial commit
> The MPOL_F_NUMA_BALANCING document was inadvertently omitted from the
> initial commit bda420b98505 ("numa balancing: migrate on fault among
> multiple bound nodes")
>
> Let's ensure its inclusion.
>
> Signed-off-by: Yafang Shao <laoar.shao at gmail.com>
> Cc: "Huang, Ying" <ying.huang at intel.com>

LGTM, Thanks!

Reviewed-by: "Huang, Ying" <ying.huang at intel.com>

> ---
>  .../admin-guide/mm/numa_memory_policy.rst     | 27 +++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
> index eca38fa81e0f..19071b71979c 100644
> --- a/Documentation/admin-guide/mm/numa_memory_policy.rst
> +++ b/Documentation/admin-guide/mm/numa_memory_policy.rst
> @@ -332,6 +332,33 @@ MPOL_F_RELATIVE_NODES
>  	MPOL_PREFERRED policies that were created with an empty nodemask
>  	(local allocation).
>  
> +MPOL_F_NUMA_BALANCING (since Linux 5.12)
> +        When operating in MPOL_BIND mode, enables NUMA balancing for tasks,
> +        contingent upon kernel support. This feature optimizes page
> +        placement within the confines of the specified memory binding
> +        policy. The addition of the MPOL_F_NUMA_BALANCING flag augments the
> +        control mechanism for NUMA balancing:
> +
> +        - The sysctl knob numa_balancing governs global activation or
> +          deactivation of NUMA balancing.
> +
> +        - Even if sysctl numa_balancing is enabled, NUMA balancing remains
> +          disabled by default for memory areas or applications utilizing
> +          explicit memory policies.
> +
> +        - The MPOL_F_NUMA_BALANCING flag facilitates NUMA balancing
> +          activation for applications employing explicit memory policies
> +          (MPOL_BIND).
> +
> +        This flags enables various optimizations for page placement through
> +        NUMA balancing. For instance, when an application's memory is bound
> +        to multiple nodes (MPOL_BIND), the hint page fault handler attempts
> +        to migrate accessed pages to reduce cross-node access if the
> +        accessing node aligns with the policy nodemask.
> +
> +        If the flag isn't supported by the kernel, or is used with mode
> +        other than MPOL_BIND, -1 is returned and errno is set to EINVAL.
> +
>  Memory Policy Reference Counting
>  ================================

--
Best Regards,
Huang, Ying