[PATCH v6 08/12] mm/mempolicy: add userland mempolicy arg structure

[Gregory Price <gourry.memverge@xxxxxxxxx>]

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@xxxxxxxxxx>
Suggested-by: Vinicius Tavares Petrucci <vtavarespetr@xxxxxxxxxx>
Suggested-by: Hasan Al Maruf <Hasan.Maruf@xxxxxxx>
Signed-off-by: Gregory Price <gregory.price@xxxxxxxxxxxx>
Co-developed-by: Vinicius Tavares Petrucci <vtavarespetr@xxxxxxxxxx>
Signed-off-by: Vinicius Tavares Petrucci <vtavarespetr@xxxxxxxxxx>
---
 .../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 */
+	};
+
+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/linux/syscalls.h b/include/linux/syscalls.h
index fd9d12de7e92..fb0b4b2b9bea 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -74,6 +74,7 @@ struct landlock_ruleset_attr;
 enum landlock_rule_type;
 struct cachestat_range;
 struct cachestat;
+struct mpol_param;
 
 #include <linux/types.h>
 #include <linux/aio_abi.h>
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)
-- 
2.39.1