[RFC PATCH] mm/mempolicy: add MPOL_PREFERRED_STRICT memory policy

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This mempolicy mode can be used with either the set_mempolicy(2)
or mbind(2) interfaces.  Like the MPOL_PREFERRED interface, it
allows an application to set a preference node from which the kernel
will fulfill memory allocation requests. Unlike the MPOL_PREFERRED mode,
it takes a set of nodes. The nodes in the nodemask are used as fallback
allocation nodes if memory is not available on the preferred node.
Unlike MPOL_PREFERRED_MANY, it will not fall back memory allocations
to all nodes in the system. Like the MPOL_BIND interface, it works over a
set of nodes and will cause a SIGSEGV or invoke the OOM killer if
memory is not available on those preferred nodes.

This patch helps applications to hint a memory allocation preference node
and fallback to _only_ a set of nodes if the memory is not available
on the preferred node.  Fallback allocation is attempted from the node which is
nearest to the preferred node.

This new memory policy helps applications to have explicit control on slow
memory allocation and avoids default fallback to slow memory NUMA nodes.
The difference with MPOL_BIND is the ability to specify a preferred node
which is the first node in the nodemask argument passed.

Cc: Ben Widawsky <ben.widawsky@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Feng Tang <feng.tang@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>b

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
 .../admin-guide/mm/numa_memory_policy.rst     |  7 +++
 include/uapi/linux/mempolicy.h                |  1 +
 mm/mempolicy.c                                | 43 +++++++++++++++++--
 3 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
index 64fd0ba0d057..4dfdcbd22d67 100644
--- a/Documentation/admin-guide/mm/numa_memory_policy.rst
+++ b/Documentation/admin-guide/mm/numa_memory_policy.rst
@@ -252,6 +252,13 @@ MPOL_PREFERRED_MANY
 	can fall back to all existing numa nodes. This is effectively
 	MPOL_PREFERRED allowed for a mask rather than a single node.
 
+MPOL_PREFERRED_STRICT
+	This mode specifies that the allocation should be attempted
+	from the first node specified in the nodemask of the policy.
+	If that allocation fails, the kernel will search other nodes
+	in the nodemask, in order of increasing distance from the
+	preferred node based on information provided by the platform firmware.
+
 NUMA memory policy supports the following optional mode flags:
 
 MPOL_F_STATIC_NODES
diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
index 046d0ccba4cd..8aa1d1963235 100644
--- a/include/uapi/linux/mempolicy.h
+++ b/include/uapi/linux/mempolicy.h
@@ -23,6 +23,7 @@ enum {
 	MPOL_INTERLEAVE,
 	MPOL_LOCAL,
 	MPOL_PREFERRED_MANY,
+	MPOL_PREFERRED_STRICT,
 	MPOL_MAX,	/* always last member of enum */
 };
 
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 1592b081c58e..59080dd1ea69 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -407,6 +407,10 @@ static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
 		.create = mpol_new_nodemask,
 		.rebind = mpol_rebind_preferred,
 	},
+	[MPOL_PREFERRED_STRICT] = {
+		.create = mpol_new_nodemask,
+		.rebind = mpol_rebind_preferred,
+	},
 };
 
 static int migrate_page_add(struct page *page, struct list_head *pagelist,
@@ -900,6 +904,7 @@ static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes)
 	case MPOL_INTERLEAVE:
 	case MPOL_PREFERRED:
 	case MPOL_PREFERRED_MANY:
+	case MPOL_PREFERRED_STRICT:
 		*nodes = p->nodes;
 		break;
 	case MPOL_LOCAL:
@@ -1781,7 +1786,7 @@ nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *policy)
 		cpuset_nodemask_valid_mems_allowed(&policy->nodes))
 		return &policy->nodes;
 
-	if (mode == MPOL_PREFERRED_MANY)
+	if (mode == MPOL_PREFERRED_MANY || mode == MPOL_PREFERRED_STRICT)
 		return &policy->nodes;
 
 	return NULL;
@@ -1796,7 +1801,7 @@ nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *policy)
  */
 static int policy_node(gfp_t gfp, struct mempolicy *policy, int nd)
 {
-	if (policy->mode == MPOL_PREFERRED) {
+	if (policy->mode == MPOL_PREFERRED || policy->mode == MPOL_PREFERRED_STRICT) {
 		nd = first_node(policy->nodes);
 	} else {
 		/*
@@ -1840,6 +1845,7 @@ unsigned int mempolicy_slab_node(void)
 
 	switch (policy->mode) {
 	case MPOL_PREFERRED:
+	case MPOL_PREFERRED_STRICT:
 		return first_node(policy->nodes);
 
 	case MPOL_INTERLEAVE:
@@ -1952,7 +1958,8 @@ int huge_node(struct vm_area_struct *vma, unsigned long addr, gfp_t gfp_flags,
 					huge_page_shift(hstate_vma(vma)));
 	} else {
 		nid = policy_node(gfp_flags, *mpol, numa_node_id());
-		if (mode == MPOL_BIND || mode == MPOL_PREFERRED_MANY)
+		if (mode == MPOL_BIND || mode == MPOL_PREFERRED_MANY ||
+			mode == MPOL_PREFERRED_STRICT)
 			*nodemask = &(*mpol)->nodes;
 	}
 	return nid;
@@ -1986,6 +1993,7 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
 	switch (mempolicy->mode) {
 	case MPOL_PREFERRED:
 	case MPOL_PREFERRED_MANY:
+	case MPOL_PREFERRED_STRICT:
 	case MPOL_BIND:
 	case MPOL_INTERLEAVE:
 		*mask = mempolicy->nodes;
@@ -2072,6 +2080,23 @@ static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
 	return page;
 }
 
+static struct page *alloc_pages_preferred_strict(gfp_t gfp, unsigned int order,
+						 struct mempolicy *pol)
+{
+	int nid;
+	gfp_t preferred_gfp;
+
+	/*
+	 * With MPOL_PREFERRED_STRICT first node in the policy nodemask
+	 * is picked as the preferred node id and the fallback allocation
+	 * is still restricted to the preferred nodes in the nodemask.
+	 */
+	preferred_gfp = gfp | __GFP_NOWARN;
+	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
+	nid = first_node(pol->nodes);
+	return __alloc_pages(preferred_gfp, order, nid, &pol->nodes);
+}
+
 /**
  * alloc_pages_vma - Allocate a page for a VMA.
  * @gfp: GFP flags.
@@ -2113,6 +2138,12 @@ struct page *alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
 		goto out;
 	}
 
+	if (pol->mode == MPOL_PREFERRED_STRICT) {
+		page = alloc_pages_preferred_strict(gfp, order, pol);
+		mpol_cond_put(pol);
+		goto out;
+	}
+
 	if (unlikely(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && hugepage)) {
 		int hpage_node = node;
 
@@ -2193,6 +2224,8 @@ struct page *alloc_pages(gfp_t gfp, unsigned order)
 	else if (pol->mode == MPOL_PREFERRED_MANY)
 		page = alloc_pages_preferred_many(gfp, order,
 				numa_node_id(), pol);
+	else if (pol->mode == MPOL_PREFERRED_STRICT)
+		page = alloc_pages_preferred_strict(gfp, order, pol);
 	else
 		page = __alloc_pages(gfp, order,
 				policy_node(gfp, pol, numa_node_id()),
@@ -2265,6 +2298,7 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
 	case MPOL_INTERLEAVE:
 	case MPOL_PREFERRED:
 	case MPOL_PREFERRED_MANY:
+	case MPOL_PREFERRED_STRICT:
 		return !!nodes_equal(a->nodes, b->nodes);
 	case MPOL_LOCAL:
 		return true;
@@ -2405,6 +2439,7 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long
 		break;
 
 	case MPOL_PREFERRED:
+	case MPOL_PREFERRED_STRICT:
 		if (node_isset(curnid, pol->nodes))
 			goto out;
 		polnid = first_node(pol->nodes);
@@ -2866,6 +2901,7 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
 			err = 0;
 		goto out;
 	case MPOL_PREFERRED_MANY:
+	case MPOL_PREFERRED_STRICT:
 	case MPOL_BIND:
 		/*
 		 * Insist on a nodelist
@@ -2953,6 +2989,7 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 		break;
 	case MPOL_PREFERRED:
 	case MPOL_PREFERRED_MANY:
+	case MPOL_PREFERRED_STRICT:
 	case MPOL_BIND:
 	case MPOL_INTERLEAVE:
 		nodes = pol->nodes;
-- 
2.31.1





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