[PATCH 1/2] mm: Replace nr_node_ids for loop with for_each_node in list lru

[Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>]

The functions used in the patch are in slowpath, which gets called
whenever alloc_super is called during mounts.

Though this should not make difference for the architectures with
sequential numa node ids, for the powerpc which can potentially have
sparse node ids (for e.g., 4 node system having numa ids, 0,1,16,17
is common), this patch saves some unnecessary allocations for
non existing numa nodes.

Even without that saving, perhaps patch makes code more readable.

Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
---
 mm/list_lru.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 909eca2..5a97f83 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -377,7 +377,7 @@ static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 {
 	int i;
 
-	for (i = 0; i < nr_node_ids; i++) {
+	for_each_node(i) {
 		if (!memcg_aware)
 			lru->node[i].memcg_lrus = NULL;
 		else if (memcg_init_list_lru_node(&lru->node[i]))
@@ -385,8 +385,11 @@ static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 	}
 	return 0;
 fail:
-	for (i = i - 1; i >= 0; i--)
+	for (i = i - 1; i >= 0; i--) {
+		if (!lru->node[i].memcg_lrus)
+			continue;
 		memcg_destroy_list_lru_node(&lru->node[i]);
+	}
 	return -ENOMEM;
 }
 
@@ -397,7 +400,7 @@ static void memcg_destroy_list_lru(struct list_lru *lru)
 	if (!list_lru_memcg_aware(lru))
 		return;
 
-	for (i = 0; i < nr_node_ids; i++)
+	for_each_node(i)
 		memcg_destroy_list_lru_node(&lru->node[i]);
 }
 
@@ -409,16 +412,20 @@ static int memcg_update_list_lru(struct list_lru *lru,
 	if (!list_lru_memcg_aware(lru))
 		return 0;
 
-	for (i = 0; i < nr_node_ids; i++) {
+	for_each_node(i) {
 		if (memcg_update_list_lru_node(&lru->node[i],
 					       old_size, new_size))
 			goto fail;
 	}
 	return 0;
 fail:
-	for (i = i - 1; i >= 0; i--)
+	for (i = i - 1; i >= 0; i--) {
+		if (!lru->node[i].memcg_lrus)
+			continue;
+
 		memcg_cancel_update_list_lru_node(&lru->node[i],
 						  old_size, new_size);
+	}
 	return -ENOMEM;
 }
 
@@ -430,7 +437,7 @@ static void memcg_cancel_update_list_lru(struct list_lru *lru,
 	if (!list_lru_memcg_aware(lru))
 		return;
 
-	for (i = 0; i < nr_node_ids; i++)
+	for_each_node(i)
 		memcg_cancel_update_list_lru_node(&lru->node[i],
 						  old_size, new_size);
 }
@@ -485,7 +492,7 @@ static void memcg_drain_list_lru(struct list_lru *lru,
 	if (!list_lru_memcg_aware(lru))
 		return;
 
-	for (i = 0; i < nr_node_ids; i++)
+	for_each_node(i)
 		memcg_drain_list_lru_node(&lru->node[i], src_idx, dst_idx);
 }
 
@@ -522,7 +529,7 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 	if (!lru->node)
 		goto out;
 
-	for (i = 0; i < nr_node_ids; i++) {
+	for_each_node(i) {
 		spin_lock_init(&lru->node[i].lock);
 		if (key)
 			lockdep_set_class(&lru->node[i].lock, key);
-- 
1.7.11.7

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