linux-kernel - Re: [PATCH v6 08/12] mm/mempolicy: add userland mempolicy arg structure

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Date: Wed, 3 Jan 2024 16:19:03 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Gregory Price <gourry.memverge@...il.com>, linux-mm@...ck.org
Cc: linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
 linux-arch@...r.kernel.org, akpm@...ux-foundation.org, arnd@...db.de,
 tglx@...utronix.de, luto@...nel.org, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, mhocko@...nel.org,
 tj@...nel.org, ying.huang@...el.com, gregory.price@...verge.com,
 corbet@....net, rakie.kim@...com, hyeongtak.ji@...com, honggyu.kim@...com,
 vtavarespetr@...ron.com, peterz@...radead.org, jgroves@...ron.com,
 ravis.opensrc@...ron.com, sthanneeru@...ron.com, emirakhur@...ron.com,
 Hasan.Maruf@....com, seungjun.ha@...sung.com,
 Frank van der Linden <fvdl@...gle.com>
Subject: Re: [PATCH v6 08/12] mm/mempolicy: add userland mempolicy arg
 structure

Hi,

On 1/3/24 14:42, Gregory Price wrote:
> This patch adds the new user-api argument structure intended for
> set_mempolicy2 and mbind2.
> 
> struct mpol_param {
>   __u16 mode;
>   __u16 mode_flags;
>   __s32 home_node;          /* mbind2: policy home node */
>   __u16 pol_maxnodes;
>   __u8 resv[6];
>   __aligned_u64 *pol_nodes;
> };
> 
> This structure is intended to be extensible as new mempolicy extensions
> are added.
> 
> For example, set_mempolicy_home_node was added to allow vma mempolicies
> to have a preferred/home node assigned.  This structure allows the user
> to set the home node at the time mempolicy is created, rather than
> requiring an additional syscalls.
> 
> Full breakdown of arguments as of this patch:
>     mode:         Mempolicy mode (MPOL_DEFAULT, MPOL_INTERLEAVE)
> 
>     mode_flags:   Flags previously or'd into mode in set_mempolicy
>                   (e.g.: MPOL_F_STATIC_NODES, MPOL_F_RELATIVE_NODES)
> 
>     home_node:    for mbind2.  Allows the setting of a policy's home
>                   with the use of MPOL_MF_HOME_NODE
> 
>     pol_maxnodes: Max number of nodes in the policy nodemask
> 
>     pol_nodes:    Policy nodemask
> 
> The reserved field accounts explicitly for a potential memory hole
> in the structure.
> 
> Suggested-by: Frank van der Linden <fvdl@...gle.com>
> Suggested-by: Vinicius Tavares Petrucci <vtavarespetr@...ron.com>
> Suggested-by: Hasan Al Maruf <Hasan.Maruf@....com>
> Signed-off-by: Gregory Price <gregory.price@...verge.com>
> Co-developed-by: Vinicius Tavares Petrucci <vtavarespetr@...ron.com>
> Signed-off-by: Vinicius Tavares Petrucci <vtavarespetr@...ron.com>
> ---
>  .../admin-guide/mm/numa_memory_policy.rst       | 17 +++++++++++++++++
>  include/linux/syscalls.h                        |  1 +
>  include/uapi/linux/mempolicy.h                  |  9 +++++++++
>  3 files changed, 27 insertions(+)
> 
> diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
> index a70f20ce1ffb..cbfc5f65ed77 100644
> --- a/Documentation/admin-guide/mm/numa_memory_policy.rst
> +++ b/Documentation/admin-guide/mm/numa_memory_policy.rst
> @@ -480,6 +480,23 @@ closest to which page allocation will come from. Specifying the home node overri
>  the default allocation policy to allocate memory close to the local node for an
>  executing CPU.
>  
> +Extended Mempolicy Arguments::
> +
> +	struct mpol_param {
> +		__u16 mode;
> +		__u16 mode_flags;
> +		__s32 home_node;	 /* mbind2: set home node */
> +		__u64 pol_maxnodes;
> +		__aligned_u64 pol_nodes; /* nodemask pointer */
> +	};
>

Can you make the above documentation struct agree with the
struct in the header below, please?
(just a difference in the size of pol_maxnodes and the
'resv' bytes)


> +The extended mempolicy argument structure is defined to allow the mempolicy
> +interfaces future extensibility without the need for additional system calls.
> +
> +The core arguments (mode, mode_flags, pol_nodes, and pol_maxnodes) apply to
> +all interfaces relative to their non-extended counterparts. Each additional
> +field may only apply to specific extended interfaces.  See the respective
> +extended interface man page for more details.
>  
>  Memory Policy Command Line Interface
>  ====================================


> diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
> index 1f9bb10d1a47..109788c8be92 100644
> --- a/include/uapi/linux/mempolicy.h
> +++ b/include/uapi/linux/mempolicy.h
> @@ -27,6 +27,15 @@ enum {
>  	MPOL_MAX,	/* always last member of enum */
>  };
>  
> +struct mpol_param {
> +	__u16 mode;
> +	__u16 mode_flags;
> +	__s32 home_node;	/* mbind2: policy home node */
> +	__u16 pol_maxnodes;
> +	__u8 resv[6];
> +	__aligned_u64 pol_nodes;
> +};
> +
>  /* Flags for set_mempolicy */
>  #define MPOL_F_STATIC_NODES	(1 << 15)
>  #define MPOL_F_RELATIVE_NODES	(1 << 14)

-- 
#Randy