mm/mmap.c: use helper macro K()

Use helper macro K() to improve code readability.  No functional
modification involved.

Link: https://lkml.kernel.org/r/20230804012559.2617515-7-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c

@@ -3785,7 +3785,7 @@ static int init_user_reserve(void)
 {
 	unsigned long free_kbytes;
 
-	free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
+	free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));
 
 	sysctl_user_reserve_kbytes = min(free_kbytes / 32, 1UL << 17);
 	return 0;
@@ -3806,7 +3806,7 @@ static int init_admin_reserve(void)
 {
 	unsigned long free_kbytes;
 
-	free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
+	free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));
 
 	sysctl_admin_reserve_kbytes = min(free_kbytes / 32, 1UL << 13);
 	return 0;
@@ -3850,7 +3850,7 @@ static int reserve_mem_notifier(struct notifier_block *nb,
 
 		break;
 	case MEM_OFFLINE:
-		free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
+		free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));
 
 		if (sysctl_user_reserve_kbytes > free_kbytes) {
 			init_user_reserve();