mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving

When a system has multiple NUMA nodes and it becomes bandwidth hungry,
using the current MPOL_INTERLEAVE could be an wise option.

However, if those NUMA nodes consist of different types of memory such as
socket-attached DRAM and CXL/PCIe attached DRAM, the round-robin based
interleave policy does not optimally distribute data to make use of their
different bandwidth characteristics.

Instead, interleave is more effective when the allocation policy follows
each NUMA nodes' bandwidth weight rather than a simple 1:1 distribution.

This patch introduces a new memory policy, MPOL_WEIGHTED_INTERLEAVE,
enabling weighted interleave between NUMA nodes.  Weighted interleave
allows for proportional distribution of memory across multiple numa nodes,
preferably apportioned to match the bandwidth of each node.

For example, if a system has 1 CPU node (0), and 2 memory nodes (0,1),
with bandwidth of (100GB/s, 50GB/s) respectively, the appropriate weight
distribution is (2:1).

Weights for each node can be assigned via the new sysfs extension:
/sys/kernel/mm/mempolicy/weighted_interleave/

For now, the default value of all nodes will be `1`, which matches the
behavior of standard 1:1 round-robin interleave.  An extension will be
added in the future to allow default values to be registered at kernel and
device bringup time.

The policy allocates a number of pages equal to the set weights.  For
example, if the weights are (2,1), then 2 pages will be allocated on node0
for every 1 page allocated on node1.

The new flag MPOL_WEIGHTED_INTERLEAVE can be used in set_mempolicy(2)
and mbind(2).

Some high level notes about the pieces of weighted interleave:

current->il_prev:
    Tracks the node previously allocated from.

current->il_weight:
    The active weight of the current node (current->il_prev)
    When this reaches 0, current->il_prev is set to the next node
    and current->il_weight is set to the next weight.

weighted_interleave_nodes:
    Counts the number of allocations as they occur, and applies the
    weight for the current node.  When the weight reaches 0, switch
    to the next node.  Operates only on task->mempolicy.

weighted_interleave_nid:
    Gets the total weight of the nodemask as well as each individual
    node weight, then calculates the node based on the given index.
    Operates on VMA policies.

bulk_array_weighted_interleave:
    Gets the total weight of the nodemask as well as each individual
    node weight, then calculates the number of "interleave rounds" as
    well as any delta ("partial round").  Calculates the number of
    pages for each node and allocates them.

    If a node was scheduled for interleave via interleave_nodes, the
    current weight will be allocated first.

    Operates only on the task->mempolicy.

One piece of complexity is the interaction between a recent refactor which
split the logic to acquire the "ilx" (interleave index) of an allocation
and the actually application of the interleave.  If a call to
alloc_pages_mpol() were made with a weighted-interleave policy and ilx set
to NO_INTERLEAVE_INDEX, weighted_interleave_nodes() would operate on a VMA
policy - violating the description above.

An inspection of all callers of alloc_pages_mpol() shows that all external
callers set ilx to `0`, an index value, or will call get_vma_policy() to
acquire the ilx.

For example, mm/shmem.c may call into alloc_pages_mpol.  The call stacks
all set (pgoff_t ilx) or end up in `get_vma_policy()`.  This enforces the
`weighted_interleave_nodes()` and `weighted_interleave_nid()` policy
requirements (task/vma respectively).

Link: https://lkml.kernel.org/r/20240202170238.90004-4-gregory.price@memverge.comSuggested-by: Hasan Al Maruf <Hasan.Maruf@amd.com>
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Co-developed-by: Rakie Kim <rakie.kim@sk.com>
Signed-off-by: Rakie Kim <rakie.kim@sk.com>
Co-developed-by: Honggyu Kim <honggyu.kim@sk.com>
Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
Co-developed-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
Signed-off-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
Co-developed-by: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
Signed-off-by: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
Co-developed-by: Ravi Jonnalagadda <ravis.opensrc@micron.com>
Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@micron.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/admin-guide/mm/numa_memory_policy.rst

@@ -250,6 +250,15 @@ 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_WEIGHTED_INTERLEAVE
+	This mode operates the same as MPOL_INTERLEAVE, except that
+	interleaving behavior is executed based on weights set in
+	/sys/kernel/mm/mempolicy/weighted_interleave/
+
+	Weighted interleave allocates pages on nodes according to a
+	weight.  For example if nodes [0,1] are weighted [5,2], 5 pages
+	will be allocated on node0 for every 2 pages allocated on node1.
+
 NUMA memory policy supports the following optional mode flags:
 
 MPOL_F_STATIC_NODES

include/linux/sched.h

@@ -1259,6 +1259,7 @@ struct task_struct {
 	/* Protected by alloc_lock: */
 	struct mempolicy		*mempolicy;
 	short				il_prev;
+	u8				il_weight;
 	short				pref_node_fork;
 #endif
 #ifdef CONFIG_NUMA_BALANCING

include/uapi/linux/mempolicy.h

@@ -23,6 +23,7 @@ enum {
 	MPOL_INTERLEAVE,
 	MPOL_LOCAL,
 	MPOL_PREFERRED_MANY,
+	MPOL_WEIGHTED_INTERLEAVE,
 	MPOL_MAX,	/* always last member of enum */
 };
 

mm/mempolicy.c

@@ -19,6 +19,13 @@
  *                for anonymous memory. For process policy an process counter
  *                is used.
  *
+ * weighted interleave
+ *                Allocate memory interleaved over a set of nodes based on
+ *                a set of weights (per-node), with normal fallback if it
+ *                fails.  Otherwise operates the same as interleave.
+ *                Example: nodeset(0,1) & weights (2,1) - 2 pages allocated
+ *                on node 0 for every 1 page allocated on node 1.
+ *
  * bind           Only allocate memory on a specific set of nodes,
  *                no fallback.
  *                FIXME: memory is allocated starting with the first node
@@ -441,6 +448,10 @@ static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
 		.create = mpol_new_nodemask,
 		.rebind = mpol_rebind_preferred,
 	},
+	[MPOL_WEIGHTED_INTERLEAVE] = {
+		.create = mpol_new_nodemask,
+		.rebind = mpol_rebind_nodemask,
+	},
 };
 
 static bool migrate_folio_add(struct folio *folio, struct list_head *foliolist,
@@ -858,8 +869,11 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
 
 	old = current->mempolicy;
 	current->mempolicy = new;
-	if (new && new->mode == MPOL_INTERLEAVE)
+	if (new && (new->mode == MPOL_INTERLEAVE ||
+		    new->mode == MPOL_WEIGHTED_INTERLEAVE)) {
 		current->il_prev = MAX_NUMNODES-1;
+		current->il_weight = 0;
+	}
 	task_unlock(current);
 	mpol_put(old);
 	ret = 0;
@@ -884,6 +898,7 @@ static void get_policy_nodemask(struct mempolicy *pol, nodemask_t *nodes)
 	case MPOL_INTERLEAVE:
 	case MPOL_PREFERRED:
 	case MPOL_PREFERRED_MANY:
+	case MPOL_WEIGHTED_INTERLEAVE:
 		*nodes = pol->nodes;
 		break;
 	case MPOL_LOCAL:
@@ -968,6 +983,13 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
 		} else if (pol == current->mempolicy &&
 				pol->mode == MPOL_INTERLEAVE) {
 			*policy = next_node_in(current->il_prev, pol->nodes);
+		} else if (pol == current->mempolicy &&
+				pol->mode == MPOL_WEIGHTED_INTERLEAVE) {
+			if (current->il_weight)
+				*policy = current->il_prev;
+			else
+				*policy = next_node_in(current->il_prev,
+						       pol->nodes);
 		} else {
 			err = -EINVAL;
 			goto out;
@@ -1332,7 +1354,8 @@ static long do_mbind(unsigned long start, unsigned long len,
 		 * VMAs, the nodes will still be interleaved from the targeted
 		 * nodemask, but one by one may be selected differently.
 		 */
-		if (new->mode == MPOL_INTERLEAVE) {
+		if (new->mode == MPOL_INTERLEAVE ||
+		    new->mode == MPOL_WEIGHTED_INTERLEAVE) {
 			struct page *page;
 			unsigned int order;
 			unsigned long addr = -EFAULT;
@@ -1780,7 +1803,8 @@ struct mempolicy *__get_vma_policy(struct vm_area_struct *vma,
  * @vma: virtual memory area whose policy is sought
  * @addr: address in @vma for shared policy lookup
  * @order: 0, or appropriate huge_page_order for interleaving
- * @ilx: interleave index (output), for use only when MPOL_INTERLEAVE
+ * @ilx: interleave index (output), for use only when MPOL_INTERLEAVE or
+ *       MPOL_WEIGHTED_INTERLEAVE
  *
  * Returns effective policy for a VMA at specified address.
  * Falls back to current->mempolicy or system default policy, as necessary.
@@ -1797,7 +1821,8 @@ struct mempolicy *get_vma_policy(struct vm_area_struct *vma,
 	pol = __get_vma_policy(vma, addr, ilx);
 	if (!pol)
 		pol = get_task_policy(current);
-	if (pol->mode == MPOL_INTERLEAVE) {
+	if (pol->mode == MPOL_INTERLEAVE ||
+	    pol->mode == MPOL_WEIGHTED_INTERLEAVE) {
 		*ilx += vma->vm_pgoff >> order;
 		*ilx += (addr - vma->vm_start) >> (PAGE_SHIFT + order);
 	}
@@ -1847,6 +1872,22 @@ bool apply_policy_zone(struct mempolicy *policy, enum zone_type zone)
 	return zone >= dynamic_policy_zone;
 }
 
+static unsigned int weighted_interleave_nodes(struct mempolicy *policy)
+{
+	unsigned int node = current->il_prev;
+
+	if (!current->il_weight || !node_isset(node, policy->nodes)) {
+		node = next_node_in(node, policy->nodes);
+		/* can only happen if nodemask is being rebound */
+		if (node == MAX_NUMNODES)
+			return node;
+		current->il_prev = node;
+		current->il_weight = get_il_weight(node);
+	}
+	current->il_weight--;
+	return node;
+}
+
 /* Do dynamic interleaving for a process */
 static unsigned int interleave_nodes(struct mempolicy *policy)
 {
@@ -1881,6 +1922,9 @@ unsigned int mempolicy_slab_node(void)
 	case MPOL_INTERLEAVE:
 		return interleave_nodes(policy);
 
+	case MPOL_WEIGHTED_INTERLEAVE:
+		return weighted_interleave_nodes(policy);
+
 	case MPOL_BIND:
 	case MPOL_PREFERRED_MANY:
 	{
@@ -1919,6 +1963,45 @@ static unsigned int read_once_policy_nodemask(struct mempolicy *pol,
 	return nodes_weight(*mask);
 }
 
+static unsigned int weighted_interleave_nid(struct mempolicy *pol, pgoff_t ilx)
+{
+	nodemask_t nodemask;
+	unsigned int target, nr_nodes;
+	u8 *table;
+	unsigned int weight_total = 0;
+	u8 weight;
+	int nid;
+
+	nr_nodes = read_once_policy_nodemask(pol, &nodemask);
+	if (!nr_nodes)
+		return numa_node_id();
+
+	rcu_read_lock();
+	table = rcu_dereference(iw_table);
+	/* calculate the total weight */
+	for_each_node_mask(nid, nodemask) {
+		/* detect system default usage */
+		weight = table ? table[nid] : 1;
+		weight = weight ? weight : 1;
+		weight_total += weight;
+	}
+
+	/* Calculate the node offset based on totals */
+	target = ilx % weight_total;
+	nid = first_node(nodemask);
+	while (target) {
+		/* detect system default usage */
+		weight = table ? table[nid] : 1;
+		weight = weight ? weight : 1;
+		if (target < weight)
+			break;
+		target -= weight;
+		nid = next_node_in(nid, nodemask);
+	}
+	rcu_read_unlock();
+	return nid;
+}
+
 /*
  * Do static interleaving for interleave index @ilx.  Returns the ilx'th
  * node in pol->nodes (starting from ilx=0), wrapping around if ilx
@@ -1979,6 +2062,11 @@ static nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *pol,
 		*nid = (ilx == NO_INTERLEAVE_INDEX) ?
 			interleave_nodes(pol) : interleave_nid(pol, ilx);
 		break;
+	case MPOL_WEIGHTED_INTERLEAVE:
+		*nid = (ilx == NO_INTERLEAVE_INDEX) ?
+			weighted_interleave_nodes(pol) :
+			weighted_interleave_nid(pol, ilx);
+		break;
 	}
 
 	return nodemask;
@@ -2040,6 +2128,7 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
 	case MPOL_PREFERRED_MANY:
 	case MPOL_BIND:
 	case MPOL_INTERLEAVE:
+	case MPOL_WEIGHTED_INTERLEAVE:
 		*mask = mempolicy->nodes;
 		break;
 
@@ -2140,6 +2229,7 @@ struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 		 * node in its nodemask, we allocate the standard way.
 		 */
 		if (pol->mode != MPOL_INTERLEAVE &&
+		    pol->mode != MPOL_WEIGHTED_INTERLEAVE &&
 		    (!nodemask || node_isset(nid, *nodemask))) {
 			/*
 			 * First, try to allocate THP only on local node, but
@@ -2275,6 +2365,114 @@ static unsigned long alloc_pages_bulk_array_interleave(gfp_t gfp,
 	return total_allocated;
 }
 
+static unsigned long alloc_pages_bulk_array_weighted_interleave(gfp_t gfp,
+		struct mempolicy *pol, unsigned long nr_pages,
+		struct page **page_array)
+{
+	struct task_struct *me = current;
+	unsigned long total_allocated = 0;
+	unsigned long nr_allocated = 0;
+	unsigned long rounds;
+	unsigned long node_pages, delta;
+	u8 *table, *weights, weight;
+	unsigned int weight_total = 0;
+	unsigned long rem_pages = nr_pages;
+	nodemask_t nodes;
+	int nnodes, node;
+	int resume_node = MAX_NUMNODES - 1;
+	u8 resume_weight = 0;
+	int prev_node;
+	int i;
+
+	if (!nr_pages)
+		return 0;
+
+	nnodes = read_once_policy_nodemask(pol, &nodes);
+	if (!nnodes)
+		return 0;
+
+	/* Continue allocating from most recent node and adjust the nr_pages */
+	node = me->il_prev;
+	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,
+						  NULL, page_array);
+		page_array += nr_allocated;
+		total_allocated += nr_allocated;
+		/* if that's all the pages, no need to interleave */
+		if (rem_pages <= weight) {
+			me->il_weight -= rem_pages;
+			return total_allocated;
+		}
+		/* Otherwise we adjust remaining pages, continue from there */
+		rem_pages -= weight;
+	}
+	/* clear active weight in case of an allocation failure */
+	me->il_weight = 0;
+	prev_node = node;
+
+	/* create a local copy of node weights to operate on outside rcu */
+	weights = kzalloc(nr_node_ids, GFP_KERNEL);
+	if (!weights)
+		return total_allocated;
+
+	rcu_read_lock();
+	table = rcu_dereference(iw_table);
+	if (table)
+		memcpy(weights, table, nr_node_ids);
+	rcu_read_unlock();
+
+	/* calculate total, detect system default usage */
+	for_each_node_mask(node, nodes) {
+		if (!weights[node])
+			weights[node] = 1;
+		weight_total += weights[node];
+	}
+
+	/*
+	 * Calculate rounds/partial rounds to minimize __alloc_pages_bulk calls.
+	 * Track which node weighted interleave should resume from.
+	 *
+	 * if (rounds > 0) and (delta == 0), resume_node will always be
+	 * the node following prev_node and its weight.
+	 */
+	rounds = rem_pages / weight_total;
+	delta = rem_pages % weight_total;
+	resume_node = next_node_in(prev_node, nodes);
+	resume_weight = weights[resume_node];
+	for (i = 0; i < nnodes; i++) {
+		node = next_node_in(prev_node, nodes);
+		weight = weights[node];
+		node_pages = weight * rounds;
+		/* If a delta exists, add this node's portion of the delta */
+		if (delta > weight) {
+			node_pages += weight;
+			delta -= weight;
+		} else if (delta) {
+			/* when delta is depleted, resume from that node */
+			node_pages += delta;
+			resume_node = node;
+			resume_weight = weight - delta;
+			delta = 0;
+		}
+		/* 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,
+						  NULL, page_array);
+		page_array += nr_allocated;
+		total_allocated += nr_allocated;
+		if (total_allocated == nr_pages)
+			break;
+		prev_node = node;
+	}
+	me->il_prev = resume_node;
+	me->il_weight = resume_weight;
+	kfree(weights);
+	return total_allocated;
+}
+
 static unsigned long alloc_pages_bulk_array_preferred_many(gfp_t gfp, int nid,
 		struct mempolicy *pol, unsigned long nr_pages,
 		struct page **page_array)
@@ -2315,6 +2513,10 @@ unsigned long alloc_pages_bulk_array_mempolicy(gfp_t gfp,
 		return alloc_pages_bulk_array_interleave(gfp, pol,
 							 nr_pages, page_array);
 
+	if (pol->mode == MPOL_WEIGHTED_INTERLEAVE)
+		return alloc_pages_bulk_array_weighted_interleave(
+				  gfp, pol, nr_pages, page_array);
+
 	if (pol->mode == MPOL_PREFERRED_MANY)
 		return alloc_pages_bulk_array_preferred_many(gfp,
 				numa_node_id(), pol, nr_pages, page_array);
@@ -2390,6 +2592,7 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
 	case MPOL_INTERLEAVE:
 	case MPOL_PREFERRED:
 	case MPOL_PREFERRED_MANY:
+	case MPOL_WEIGHTED_INTERLEAVE:
 		return !!nodes_equal(a->nodes, b->nodes);
 	case MPOL_LOCAL:
 		return true;
@@ -2526,6 +2729,10 @@ int mpol_misplaced(struct folio *folio, struct vm_area_struct *vma,
 		polnid = interleave_nid(pol, ilx);
 		break;
 
+	case MPOL_WEIGHTED_INTERLEAVE:
+		polnid = weighted_interleave_nid(pol, ilx);
+		break;
+
 	case MPOL_PREFERRED:
 		if (node_isset(curnid, pol->nodes))
 			goto out;
@@ -2900,6 +3107,7 @@ static const char * const policy_modes[] =
 	[MPOL_PREFERRED]  = "prefer",
 	[MPOL_BIND]       = "bind",
 	[MPOL_INTERLEAVE] = "interleave",
+	[MPOL_WEIGHTED_INTERLEAVE] = "weighted interleave",
 	[MPOL_LOCAL]      = "local",
 	[MPOL_PREFERRED_MANY]  = "prefer (many)",
 };
@@ -2959,6 +3167,7 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
 		}
 		break;
 	case MPOL_INTERLEAVE:
+	case MPOL_WEIGHTED_INTERLEAVE:
 		/*
 		 * Default to online nodes with memory if no nodelist
 		 */
@@ -3069,6 +3278,7 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 	case MPOL_PREFERRED_MANY:
 	case MPOL_BIND:
 	case MPOL_INTERLEAVE:
+	case MPOL_WEIGHTED_INTERLEAVE:
 		nodes = pol->nodes;
 		break;
 	default: