Message-Id: <20231031003810.4532-5-gregory.price@memverge.com>
Date:   Mon, 30 Oct 2023 20:38:10 -0400
From:   Gregory Price <gourry.memverge@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-cxl@...r.kernel.org, linux-mm@...ck.org,
        ying.huang@...el.com, akpm@...ux-foundation.org,
        aneesh.kumar@...ux.ibm.com, weixugc@...gle.com, apopple@...dia.com,
        hannes@...xchg.org, tim.c.chen@...el.com, dave.hansen@...el.com,
        mhocko@...nel.org, shy828301@...il.com, gregkh@...uxfoundation.org,
        rafael@...nel.org, Gregory Price <gregory.price@...verge.com>
Subject: [RFC PATCH v3 4/4] mm/mempolicy: modify interleave mempolicy to use node weights

The node subsystem implements interleave weighting for the purpose
of bandwidth optimization.  Each node may have different weights in
relation to each compute node ("access node").

The mempolicy MPOL_INTERLEAVE utilizes the node weights to implement
weighted interleave.  By default, since all nodes default to a weight
of 1, the original interleave behavior is retained.

Examples

Weight settings:
echo 4 > node0/access0/il_weight
echo 1 > node0/access1/il_weight

echo 3 > node1/access0/il_weight
echo 2 > node1/access1/il_weight

Results:

Task A:
   cpunode:  0
   nodemask: [0,1]
   weights:  [4,3]
   allocation result: [0,0,0,0,1,1,1 repeat]

Task B:
   cpunode:  1
   nodemask: [0,1]
   weights:  [1,2]
   allocation result: [0,1,1 repeat]
   Weights are relative to access node

Signed-off-by: Gregory Price <gregory.price@...verge.com>
---
 include/linux/mempolicy.h |   4 ++
 mm/mempolicy.c            | 138 +++++++++++++++++++++++++++++---------
 2 files changed, 112 insertions(+), 30 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index d232de7cdc56..240468b669fd 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -48,6 +48,10 @@ struct mempolicy {
 	nodemask_t nodes;	/* interleave/bind/perfer */
 	int home_node;		/* Home node to use for MPOL_BIND and MPOL_PREFERRED_MANY */
 
+	/* weighted interleave settings */
+	unsigned char cur_weight;
+	unsigned char il_weights[MAX_NUMNODES];
+
 	union {
 		nodemask_t cpuset_mems_allowed;	/* relative to these nodes */
 		nodemask_t user_nodemask;	/* nodemask passed by user */
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 29ebf1e7898c..d62e942a13bd 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -102,6 +102,7 @@
 #include <linux/mmu_notifier.h>
 #include <linux/printk.h>
 #include <linux/swapops.h>
+#include <linux/memory-tiers.h>
 
 #include <asm/tlbflush.h>
 #include <asm/tlb.h>
@@ -300,6 +301,7 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
 	policy->mode = mode;
 	policy->flags = flags;
 	policy->home_node = NUMA_NO_NODE;
+	policy->cur_weight = 0;
 
 	return policy;
 }
@@ -334,6 +336,7 @@ static void mpol_rebind_nodemask(struct mempolicy *pol, const nodemask_t *nodes)
 		tmp = *nodes;
 
 	pol->nodes = tmp;
+	pol->cur_weight = 0;
 }
 
 static void mpol_rebind_preferred(struct mempolicy *pol,
@@ -881,8 +884,11 @@ 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) {
 		current->il_prev = MAX_NUMNODES-1;
+		new->cur_weight = 0;
+	}
+
 	task_unlock(current);
 	mpol_put(old);
 	ret = 0;
@@ -1903,12 +1909,21 @@ static int policy_node(gfp_t gfp, struct mempolicy *policy, int nd)
 /* Do dynamic interleaving for a process */
 static unsigned interleave_nodes(struct mempolicy *policy)
 {
-	unsigned next;
+	unsigned int next;
+	unsigned char next_weight;
 	struct task_struct *me = current;
 
 	next = next_node_in(me->il_prev, policy->nodes);
-	if (next < MAX_NUMNODES)
+	if (!policy->cur_weight) {
+		/* If the node is set, at least 1 allocation is required */
+		next_weight = node_get_il_weight(next, numa_node_id());
+		policy->cur_weight = next_weight ? next_weight : 1;
+	}
+
+	policy->cur_weight--;
+	if (next < MAX_NUMNODES && !policy->cur_weight)
 		me->il_prev = next;
+
 	return next;
 }
 
@@ -1967,25 +1982,37 @@ unsigned int mempolicy_slab_node(void)
 static unsigned offset_il_node(struct mempolicy *pol, unsigned long n)
 {
 	nodemask_t nodemask = pol->nodes;
-	unsigned int target, nnodes;
-	int i;
+	unsigned int target, nnodes, il_weight;
+	unsigned char weight;
 	int nid;
+	int cur_node = numa_node_id();
+
 	/*
 	 * The barrier will stabilize the nodemask in a register or on
 	 * the stack so that it will stop changing under the code.
 	 *
 	 * Between first_node() and next_node(), pol->nodes could be changed
 	 * by other threads. So we put pol->nodes in a local stack.
+	 *
+	 * Additionally, place the cur_node on the stack in case of a migration
 	 */
 	barrier();
 
 	nnodes = nodes_weight(nodemask);
 	if (!nnodes)
-		return numa_node_id();
-	target = (unsigned int)n % nnodes;
+		return cur_node;
+
+	il_weight = nodes_get_il_weights(cur_node, &nodemask, pol->il_weights);
+	target = (unsigned int)n % il_weight;
 	nid = first_node(nodemask);
-	for (i = 0; i < target; i++)
-		nid = next_node(nid, nodemask);
+	while (target) {
+		weight = pol->il_weights[nid];
+		if (target < weight)
+			break;
+		target -= weight;
+		nid = next_node_in(nid, nodemask);
+	}
+
 	return nid;
 }
 
@@ -2319,32 +2346,83 @@ static unsigned long alloc_pages_bulk_array_interleave(gfp_t gfp,
 		struct mempolicy *pol, unsigned long nr_pages,
 		struct page **page_array)
 {
-	int nodes;
-	unsigned long nr_pages_per_node;
-	int delta;
-	int i;
-	unsigned long nr_allocated;
+	struct task_struct *me = current;
 	unsigned long total_allocated = 0;
+	unsigned long nr_allocated;
+	unsigned long rounds;
+	unsigned long node_pages, delta;
+	unsigned char weight;
+	unsigned long il_weight;
+	unsigned long req_pages = nr_pages;
+	int nnodes, node, prev_node;
+	int cur_node = numa_node_id();
+	int i;
 
-	nodes = nodes_weight(pol->nodes);
-	nr_pages_per_node = nr_pages / nodes;
-	delta = nr_pages - nodes * nr_pages_per_node;
-
-	for (i = 0; i < nodes; i++) {
-		if (delta) {
-			nr_allocated = __alloc_pages_bulk(gfp,
-					interleave_nodes(pol), NULL,
-					nr_pages_per_node + 1, NULL,
-					page_array);
-			delta--;
-		} else {
-			nr_allocated = __alloc_pages_bulk(gfp,
-					interleave_nodes(pol), NULL,
-					nr_pages_per_node, NULL, page_array);
+	prev_node = me->il_prev;
+	nnodes = nodes_weight(pol->nodes);
+	/* Continue allocating from most recent node */
+	if (pol->cur_weight) {
+		node = next_node_in(prev_node, pol->nodes);
+		node_pages = pol->cur_weight;
+		if (node_pages > nr_pages)
+			node_pages = nr_pages;
+		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 (req_pages <= pol->cur_weight) {
+			pol->cur_weight -= req_pages;
+			return total_allocated;
 		}
-
+		/* Otherwise we adjust req_pages down, and continue from there */
+		req_pages -= pol->cur_weight;
+		pol->cur_weight = 0;
+		prev_node = node;
+	}
+
+	il_weight = nodes_get_il_weights(cur_node, &pol->nodes,
+					 pol->il_weights);
+	rounds = req_pages / il_weight;
+	delta = req_pages % il_weight;
+	for (i = 0; i < nnodes; i++) {
+		node = next_node_in(prev_node, pol->nodes);
+		weight = pol->il_weights[node];
+		node_pages = weight * rounds;
+		if (delta > weight) {
+			node_pages += weight;
+			delta -= weight;
+		} else if (delta) {
+			node_pages += delta;
+			delta = 0;
+		}
+		/* The number of requested pages may not hit every node */
+		if (!node_pages)
+			break;
+		/* If an over-allocation would occur, floor it */
+		if (node_pages + total_allocated > nr_pages) {
+			node_pages = nr_pages - total_allocated;
+			delta = 0;
+		}
+		nr_allocated = __alloc_pages_bulk(gfp, node, NULL, node_pages,
+						  NULL, page_array);
 		page_array += nr_allocated;
 		total_allocated += nr_allocated;
+		prev_node = node;
+	}
+
+	/*
+	 * Finally, we need to update me->il_prev and pol->cur_weight
+	 * If the last node allocated on has un-used weight, apply
+	 * the remainder as the cur_weight, otherwise proceed to next node
+	 */
+	if (node_pages) {
+		me->il_prev = prev_node;
+		node_pages %= weight;
+		pol->cur_weight = weight - node_pages;
+	} else {
+		me->il_prev = node;
+		pol->cur_weight = 0;
 	}
 
 	return total_allocated;
-- 
2.39.1

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