mm: track NR_KERNEL_STACK in KiB instead of number of stacks

Currently, NR_KERNEL_STACK tracks the number of kernel stacks in a zone.
This only makes sense if each kernel stack exists entirely in one zone,
and allowing vmapped stacks could break this assumption.

Since frv has THREAD_SIZE < PAGE_SIZE, we need to track kernel stack
allocations in a unit that divides both THREAD_SIZE and PAGE_SIZE on all
architectures.  Keep it simple and use KiB.

Link: http://lkml.kernel.org/r/083c71e642c5fa5f1b6898902e1b2db7b48940d4.1468523549.git.luto@kernel.org
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/base/node.c

@@ -124,8 +124,7 @@ static ssize_t node_read_meminfo(struct device *dev,
 		       nid, K(node_page_state(pgdat, NR_FILE_MAPPED)),
 		       nid, K(node_page_state(pgdat, NR_ANON_MAPPED)),
 		       nid, K(i.sharedram),
-		       nid, sum_zone_node_page_state(nid, NR_KERNEL_STACK) *
-				THREAD_SIZE / 1024,
+		       nid, sum_zone_node_page_state(nid, NR_KERNEL_STACK_KB),
 		       nid, K(sum_zone_node_page_state(nid, NR_PAGETABLE)),
 		       nid, K(node_page_state(pgdat, NR_UNSTABLE_NFS)),
 		       nid, K(sum_zone_node_page_state(nid, NR_BOUNCE)),

fs/proc/meminfo.c

@@ -147,7 +147,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
 				global_page_state(NR_SLAB_UNRECLAIMABLE)),
 		K(global_page_state(NR_SLAB_RECLAIMABLE)),
 		K(global_page_state(NR_SLAB_UNRECLAIMABLE)),
-		global_page_state(NR_KERNEL_STACK) * THREAD_SIZE / 1024,
+		global_page_state(NR_KERNEL_STACK_KB),
 		K(global_page_state(NR_PAGETABLE)),
 #ifdef CONFIG_QUICKLIST
 		K(quicklist_total_size()),

include/linux/mmzone.h

@@ -121,7 +121,7 @@ enum zone_stat_item {
 	NR_SLAB_RECLAIMABLE,
 	NR_SLAB_UNRECLAIMABLE,
 	NR_PAGETABLE,		/* used for pagetables */
-	NR_KERNEL_STACK,
+	NR_KERNEL_STACK_KB,	/* measured in KiB */
 	/* Second 128 byte cacheline */
 	NR_BOUNCE,
 #if IS_ENABLED(CONFIG_ZSMALLOC)

kernel/fork.c

@@ -225,7 +225,8 @@ static void account_kernel_stack(unsigned long *stack, int account)
 {
 	struct zone *zone = page_zone(virt_to_page(stack));
 
-	mod_zone_page_state(zone, NR_KERNEL_STACK, account);
+	mod_zone_page_state(zone, NR_KERNEL_STACK_KB,
+			    THREAD_SIZE / 1024 * account);
 }
 
 void free_task(struct task_struct *tsk)

mm/page_alloc.c

@@ -4359,8 +4359,7 @@ void show_free_areas(unsigned int filter)
 			K(zone_page_state(zone, NR_MLOCK)),
 			K(zone_page_state(zone, NR_SLAB_RECLAIMABLE)),
 			K(zone_page_state(zone, NR_SLAB_UNRECLAIMABLE)),
-			zone_page_state(zone, NR_KERNEL_STACK) *
-				THREAD_SIZE / 1024,
+			zone_page_state(zone, NR_KERNEL_STACK_KB),
 			K(zone_page_state(zone, NR_PAGETABLE)),
 			K(zone_page_state(zone, NR_BOUNCE)),
 			K(free_pcp),