[PATCH v5 22/36] mm/mempolicy: add MPOL_F_PRIVATE and zonelist selection

[Gregory Price <gourry@gourry.net>]

Add MPOL_F_PRIVATE, the internal flag noting that a policy contains
a nodemask with a private node, and making private node memory
reachable via standard mempolicies.

Plumb zonelist selection into the mpol allocator interfaces via the
allocator's alloc_flags, using the alloc_flags-carrying page_alloc
interfaces.

mpol_alloc_flags() maps MPOL_F_PRIVATE to the alloc_flags an
allocation uses:
    ALLOC_DEFAULT            -  normal allocation
    ALLOC_ZONELIST_PRIVATE   -  private node allocation

With this, a VMA with (mpol->flags & MPOL_F_PRIVATE) can successfully
services faults like any other mbind() from the private node:

   buf = mmap(..., MAP_ANON);
   mbind(buf, ..., {private_node});
   buf[0] = 0xdeadbeef;  // Page faulted from private node memory

Like any other bind, the nodemask relaxes if it is unsatisfiable.

For example: apply_policy_zone() allows an unmovable allocation
targeting the VMA to fallback to a viable node instead of failing.

cpuset rebinding does not affect private nodes - the nodes in the
original mask are preserved, and we enforce two remap rules:

  1) never allow N_MEMORY nodes to remap to N_MEMORY_PRIVATE
  2) never remap N_MEMORY_PRIVATE nodes at all (they stay in place)

In the case of an empty nodemask as a result of rebind, revert to
cpuset - which never includes N_MEMORY_PRIVATE and always guarantees
at least one N_MEMORY node.

As of this patch, nothing can actually sets MPOL_F_PRIVATE, so this
is a no-op that simply adds the plumbing throughout mempolicy.

Signed-off-by: Gregory Price <gourry@gourry.net>
---
 include/uapi/linux/mempolicy.h |  1 +
 mm/mempolicy.c                 | 79 +++++++++++++++++++++++-----------
 2 files changed, 55 insertions(+), 25 deletions(-)

diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
index 7f6fc9599693b..87af18c84b947 100644
--- a/include/uapi/linux/mempolicy.h
+++ b/include/uapi/linux/mempolicy.h
@@ -67,6 +67,7 @@ enum mempolicy_mode {
 #define MPOL_F_SHARED  (1 << 0)	/* identify shared policies */
 #define MPOL_F_MOF	(1 << 3) /* this policy wants migrate on fault */
 #define MPOL_F_MORON	(1 << 4) /* Migrate On protnone Reference On Node */
+#define MPOL_F_PRIVATE	(1 << 5) /* nodemask contains private nodes */
 
 /*
  * Enabling zone reclaim means the page allocator will attempt to fulfill
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 2b76c57a460c9..90110e9761122 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -432,6 +432,10 @@ static int mpol_set_nodemask(struct mempolicy *pol,
 	else
 		pol->w.cpuset_mems_allowed = cpuset_current_mems_allowed;
 
+	/* If any private nodes left in the nodemask - add the private flag */
+	if (nodes_intersects(nsc->mask2, node_states[N_MEMORY_PRIVATE]))
+		pol->flags |= MPOL_F_PRIVATE;
+
 	ret = mpol_ops[pol->mode].create(pol, &nsc->mask2);
 	return ret;
 }
@@ -505,22 +509,33 @@ static void mpol_rebind_default(struct mempolicy *pol, const nodemask_t *nodes)
 
 static void mpol_rebind_nodemask(struct mempolicy *pol, const nodemask_t *nodes)
 {
-	nodemask_t tmp;
+	nodemask_t tmp, priv;
+
+	/* preserve online private nodes to re-add later */
+	nodes_and(priv, pol->nodes, node_states[N_MEMORY_PRIVATE]);
 
 	if (pol->flags & MPOL_F_STATIC_NODES)
 		nodes_and(tmp, pol->w.user_nodemask, *nodes);
-	else if (pol->flags & MPOL_F_RELATIVE_NODES)
-		mpol_relative_nodemask(&tmp, &pol->w.user_nodemask, nodes);
-	else {
+	else if (pol->flags & MPOL_F_RELATIVE_NODES) {
+		/* fold only the public part: a private node must not take a slot */
+		nodes_and(tmp, pol->w.user_nodemask, node_states[N_MEMORY]);
+		mpol_relative_nodemask(&tmp, &tmp, nodes);
+	} else {
 		nodes_remap(tmp, pol->nodes, pol->w.cpuset_mems_allowed,
 								*nodes);
 		pol->w.cpuset_mems_allowed = *nodes;
 	}
 
-	if (nodes_empty(tmp))
+	/* private nodes are identity-mapped during remap, drop them here */
+	nodes_and(tmp, tmp, node_states[N_MEMORY]);
+	if (nodes_empty(tmp) && nodes_empty(priv))
 		tmp = *nodes;
 
-	pol->nodes = tmp;
+	/* If any online private nodes remain, add them back */
+	nodes_or(pol->nodes, tmp, priv);
+	/* If no online private nodes remain, strip the private flag */
+	if (nodes_empty(priv))
+		pol->flags &= ~MPOL_F_PRIVATE;
 }
 
 static void mpol_rebind_preferred(struct mempolicy *pol,
@@ -2411,7 +2426,8 @@ bool mempolicy_in_oom_domain(struct task_struct *tsk,
 }
 
 static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
-						int nid, nodemask_t *nodemask)
+						int nid, nodemask_t *nodemask,
+						unsigned int aflags)
 {
 	struct page *page;
 	gfp_t preferred_gfp;
@@ -2425,14 +2441,21 @@ static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
 	preferred_gfp = gfp | __GFP_NOWARN;
 	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
 	page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid, nodemask,
-					   ALLOC_DEFAULT);
+					     aflags);
 	if (!page)
 		page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL,
-						   ALLOC_DEFAULT);
+						     aflags);
 
 	return page;
 }
 
+/* A private policy allocates from the private zonelist. */
+static inline unsigned int mpol_alloc_flags(struct mempolicy *pol)
+{
+	return (pol->flags & MPOL_F_PRIVATE) ? ALLOC_ZONELIST_PRIVATE :
+					       ALLOC_DEFAULT;
+}
+
 /**
  * alloc_pages_mpol - Allocate pages according to NUMA mempolicy.
  * @gfp: GFP flags.
@@ -2448,11 +2471,13 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 {
 	nodemask_t *nodemask;
 	struct page *page;
+	unsigned int aflags = mpol_alloc_flags(pol);
 
 	nodemask = policy_nodemask(gfp, pol, ilx, &nid);
 
 	if (pol->mode == MPOL_PREFERRED_MANY)
-		return alloc_pages_preferred_many(gfp, order, nid, nodemask);
+		return alloc_pages_preferred_many(gfp, order, nid, nodemask,
+						  aflags);
 
 	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
 	    /* filter "hugepage" allocation, unless from alloc_pages() */
@@ -2476,7 +2501,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 			 */
 			page = __alloc_frozen_pages_noprof(
 				gfp | __GFP_THISNODE | __GFP_NORETRY, order,
-				nid, NULL, ALLOC_DEFAULT);
+				nid, NULL, aflags);
 			if (page || !(gfp & __GFP_DIRECT_RECLAIM))
 				return page;
 			/*
@@ -2488,7 +2513,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 		}
 	}
 
-	page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask, ALLOC_DEFAULT);
+	page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask, aflags);
 
 	if (unlikely(pol->mode == MPOL_INTERLEAVE ||
 		     pol->mode == MPOL_WEIGHTED_INTERLEAVE) && page) {
@@ -2597,6 +2622,7 @@ static unsigned long alloc_pages_bulk_interleave(gfp_t gfp,
 		struct mempolicy *pol, unsigned long nr_pages,
 		struct page **page_array)
 {
+	unsigned int aflags = mpol_alloc_flags(pol);
 	int nodes;
 	unsigned long nr_pages_per_node;
 	int delta;
@@ -2610,14 +2636,14 @@ static unsigned long alloc_pages_bulk_interleave(gfp_t gfp,
 
 	for (i = 0; i < nodes; i++) {
 		if (delta) {
-			nr_allocated = alloc_pages_bulk_noprof(gfp,
-					interleave_nodes(pol), NULL,
+			nr_allocated = __alloc_pages_bulk_noprof(gfp,
+					aflags, interleave_nodes(pol), NULL,
 					nr_pages_per_node + 1,
 					page_array);
 			delta--;
 		} else {
-			nr_allocated = alloc_pages_bulk_noprof(gfp,
-					interleave_nodes(pol), NULL,
+			nr_allocated = __alloc_pages_bulk_noprof(gfp,
+					aflags, interleave_nodes(pol), NULL,
 					nr_pages_per_node, page_array);
 		}
 
@@ -2632,6 +2658,7 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
 		struct mempolicy *pol, unsigned long nr_pages,
 		struct page **page_array)
 {
+	unsigned int aflags = mpol_alloc_flags(pol);
 	struct weighted_interleave_state *state;
 	struct task_struct *me = current;
 	unsigned int cpuset_mems_cookie;
@@ -2667,8 +2694,8 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
 	weight = me->il_weight;
 	if (weight && node_isset(node, nodes)) {
 		node_pages = min(rem_pages, weight);
-		nr_allocated = __alloc_pages_bulk(gfp, node, NULL, node_pages,
-						  page_array);
+		nr_allocated = __alloc_pages_bulk_noprof(gfp, aflags, node,
+						  NULL, node_pages, page_array);
 		page_array += nr_allocated;
 		total_allocated += nr_allocated;
 		/* if that's all the pages, no need to interleave */
@@ -2732,8 +2759,8 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
 		/* node_pages can be 0 if an allocation fails and rounds == 0 */
 		if (!node_pages)
 			break;
-		nr_allocated = __alloc_pages_bulk(gfp, node, NULL, node_pages,
-						  page_array);
+		nr_allocated = __alloc_pages_bulk_noprof(gfp, aflags, node,
+						  NULL, node_pages, page_array);
 		page_array += nr_allocated;
 		total_allocated += nr_allocated;
 		if (total_allocated == nr_pages)
@@ -2750,17 +2777,19 @@ static unsigned long alloc_pages_bulk_preferred_many(gfp_t gfp, int nid,
 		struct mempolicy *pol, unsigned long nr_pages,
 		struct page **page_array)
 {
+	unsigned int aflags = mpol_alloc_flags(pol);
 	gfp_t preferred_gfp;
 	unsigned long nr_allocated = 0;
 
 	preferred_gfp = gfp | __GFP_NOWARN;
 	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
 
-	nr_allocated  = alloc_pages_bulk_noprof(preferred_gfp, nid, &pol->nodes,
-					   nr_pages, page_array);
+	nr_allocated  = __alloc_pages_bulk_noprof(preferred_gfp, aflags,
+					   nid, &pol->nodes, nr_pages, page_array);
 
 	if (nr_allocated < nr_pages)
-		nr_allocated += alloc_pages_bulk_noprof(gfp, numa_node_id(), NULL,
+		nr_allocated += __alloc_pages_bulk_noprof(gfp, aflags,
+				numa_node_id(), NULL,
 				nr_pages - nr_allocated,
 				page_array + nr_allocated);
 	return nr_allocated;
@@ -2796,8 +2825,8 @@ unsigned long alloc_pages_bulk_mempolicy_noprof(gfp_t gfp,
 
 	nid = numa_node_id();
 	nodemask = policy_nodemask(gfp, pol, NO_INTERLEAVE_INDEX, &nid);
-	return alloc_pages_bulk_noprof(gfp, nid, nodemask,
-				       nr_pages, page_array);
+	return __alloc_pages_bulk_noprof(gfp, mpol_alloc_flags(pol), nid,
+						nodemask, nr_pages, page_array);
 }
 
 int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
-- 
2.53.0-Meta