[RFC PATCH 06/11] mm/mempolicy: allow home_node to be set by mpol_new

[Gregory Price <gourry.memverge@gmail.com>]

This patch adds the plumbing into mpol_new() to allow the argument
structure's home_node field to be set during mempolicy creation.

The syscall sys_set_mempolicy_home_node was added to allow a home
node to be registered for a vma.

For set_mempolicy2 and mbind2 syscalls, it would be useful to add
this as an extension to allow the user to submit a fully formed
mempolicy configuration in a single call, rather than require
multiple calls to configure a mempolicy.

This will become particularly useful if/when pidfd interfaces to
change process mempolicies from outside the task appear, as each
call to change the mempolicy does an atomic swap of that policy
in the task, rather than mutate the policy.

Signed-off-by: Gregory Price <gregory.price@memverge.com>
---
 mm/mempolicy.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index fecdc781b6a0..4be63547a4b3 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -311,6 +311,7 @@ static struct mempolicy *mpol_new(struct mempolicy_args *args)
 	policy->flags = flags;
 	policy->home_node = NUMA_NO_NODE;
 	policy->wil.cur_weight = 0;
+	policy->home_node = args->home_node;
 
 	return policy;
 }
@@ -1624,6 +1625,7 @@ static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
 	args.mode = lmode;
 	args.mode_flags = mode_flags;
 	args.policy_nodes = &nodes;
+	args.home_node = NUMA_NO_NODE;
 
 	return do_set_mempolicy(&args);
 }
@@ -2967,6 +2969,8 @@ void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol)
 		margs.mode = mpol->mode;
 		margs.mode_flags = mpol->flags;
 		margs.policy_nodes = &mpol->w.user_nodemask;
+		margs.home_node = NUMA_NO_NODE;
+
 		/* contextualize the tmpfs mount point mempolicy to this file */
 		npol = mpol_new(&margs);
 		if (IS_ERR(npol))
@@ -3125,6 +3129,7 @@ void __init numa_policy_init(void)
 	memset(&args, 0, sizeof(args));
 	args.mode = MPOL_INTERLEAVE;
 	args.policy_nodes = &interleave_nodes;
+	args.home_node = NUMA_NO_NODE;
 
 	if (do_set_mempolicy(&args))
 		pr_err("%s: interleaving failed\n", __func__);
@@ -3139,6 +3144,7 @@ void numa_default_policy(void)
 
 	memset(&args, 0, sizeof(args));
 	args.mode = MPOL_DEFAULT;
+	args.home_node = NUMA_NO_NODE;
 
 	do_set_mempolicy(&args);
 }
@@ -3261,6 +3267,8 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
 	margs.mode = mode;
 	margs.mode_flags = mode_flags;
 	margs.policy_nodes = &nodes;
+	margs.home_node = NUMA_NO_NODE;
+
 	new = mpol_new(&margs);
 	if (IS_ERR(new))
 		goto out;
-- 
2.39.1