[PATCH] mm/vmstat: do not use size of vmstat_text as count of /proc/vmstat items

[Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>]

Strings from vmstat_text[] will be used for printing memory cgroup
statistics which exists even if CONFIG_VM_EVENT_COUNTERS=n.

This should be applied before patch "mm/memcontrol: use vmstat names
for printing statistics".

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/linux-mm/cd1c42ae-281f-c8a8-70ac-1d01d417b2e1@xxxxxxxxxxxxx/T/#u
---
 mm/vmstat.c |   26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 590aeca27cab..13e36da70f3c 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1638,25 +1638,23 @@ static const struct seq_operations zoneinfo_op = {
 	.show	= zoneinfo_show,
 };
 
+#define NR_VMSTAT_ITEMS (NR_VM_ZONE_STAT_ITEMS + \
+			 NR_VM_NUMA_STAT_ITEMS + \
+			 NR_VM_NODE_STAT_ITEMS + \
+			 NR_VM_WRITEBACK_STAT_ITEMS + \
+			 (IS_ENABLED(CONFIG_VM_EVENT_COUNTERS) ? \
+			  NR_VM_EVENT_ITEMS : 0))
+
 static void *vmstat_start(struct seq_file *m, loff_t *pos)
 {
 	unsigned long *v;
-	int i, stat_items_size;
+	int i;
 
-	if (*pos >= ARRAY_SIZE(vmstat_text))
+	if (*pos >= NR_VMSTAT_ITEMS)
 		return NULL;
-	stat_items_size = NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long) +
-			  NR_VM_NUMA_STAT_ITEMS * sizeof(unsigned long) +
-			  NR_VM_NODE_STAT_ITEMS * sizeof(unsigned long) +
-			  NR_VM_WRITEBACK_STAT_ITEMS * sizeof(unsigned long);
-
-#ifdef CONFIG_VM_EVENT_COUNTERS
-	stat_items_size += sizeof(struct vm_event_state);
-#endif
 
-	BUILD_BUG_ON(stat_items_size !=
-		     ARRAY_SIZE(vmstat_text) * sizeof(unsigned long));
-	v = kmalloc(stat_items_size, GFP_KERNEL);
+	BUILD_BUG_ON(ARRAY_SIZE(vmstat_text) < NR_VMSTAT_ITEMS);
+	v = kmalloc_array(NR_VMSTAT_ITEMS, sizeof(unsigned long), GFP_KERNEL);
 	m->private = v;
 	if (!v)
 		return ERR_PTR(-ENOMEM);
@@ -1689,7 +1687,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos)
 {
 	(*pos)++;
-	if (*pos >= ARRAY_SIZE(vmstat_text))
+	if (*pos >= NR_VMSTAT_ITEMS)
 		return NULL;
 	return (unsigned long *)m->private + *pos;
 }