ext4: add MB_NUM_ORDERS macro

A few arrays in mballoc.c use the total number of valid orders as
their size. Currently, this value is set as "sb->s_blocksize_bits +
2". This makes code harder to read. So, instead add a new macro
MB_NUM_ORDERS(sb) to make the code more readable.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20210401172129.189766-5-harshadshirwadkar@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -756,7 +756,7 @@ mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
 
 	grp->bb_largest_free_order = -1; /* uninit */
 
-	bits = sb->s_blocksize_bits + 1;
+	bits = MB_NUM_ORDERS(sb) - 1;
 	for (i = bits; i >= 0; i--) {
 		if (grp->bb_counters[i] > 0) {
 			grp->bb_largest_free_order = i;
@@ -957,7 +957,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp)
 			grinfo->bb_fragments = 0;
 			memset(grinfo->bb_counters, 0,
 			       sizeof(*grinfo->bb_counters) *
-				(sb->s_blocksize_bits+2));
+			       (MB_NUM_ORDERS(sb)));
 			/*
 			 * incore got set to the group block bitmap below
 			 */
@@ -1928,7 +1928,7 @@ void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
 	int max;
 
 	BUG_ON(ac->ac_2order <= 0);
-	for (i = ac->ac_2order; i <= sb->s_blocksize_bits + 1; i++) {
+	for (i = ac->ac_2order; i < MB_NUM_ORDERS(sb); i++) {
 		if (grp->bb_counters[i] == 0)
 			continue;
 
@@ -2107,7 +2107,7 @@ static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
 		if (free < ac->ac_g_ex.fe_len)
 			return false;
 
-		if (ac->ac_2order > ac->ac_sb->s_blocksize_bits+1)
+		if (ac->ac_2order >= MB_NUM_ORDERS(ac->ac_sb))
 			return true;
 
 		if (grp->bb_largest_free_order < ac->ac_2order)
@@ -2315,13 +2315,13 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 	 * We also support searching for power-of-two requests only for
 	 * requests upto maximum buddy size we have constructed.
 	 */
-	if (i >= sbi->s_mb_order2_reqs && i <= sb->s_blocksize_bits + 2) {
+	if (i >= sbi->s_mb_order2_reqs && i <= MB_NUM_ORDERS(sb)) {
 		/*
 		 * This should tell if fe_len is exactly power of 2
 		 */
 		if ((ac->ac_g_ex.fe_len & (~(1 << (i - 1)))) == 0)
 			ac->ac_2order = array_index_nospec(i - 1,
-							   sb->s_blocksize_bits + 2);
+							   MB_NUM_ORDERS(sb));
 	}
 
 	/* if stream allocation is enabled, use global goal */
@@ -2880,15 +2880,15 @@ int ext4_mb_init(struct super_block *sb)
 	unsigned max;
 	int ret;
 
-	i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_offsets);
+	i = MB_NUM_ORDERS(sb) * sizeof(*sbi->s_mb_offsets);
 
 	sbi->s_mb_offsets = kmalloc(i, GFP_KERNEL);
 	if (sbi->s_mb_offsets == NULL) {
 		ret = -ENOMEM;
 		goto out;
 	}
 
-	i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_maxs);
+	i = MB_NUM_ORDERS(sb) * sizeof(*sbi->s_mb_maxs);
 	sbi->s_mb_maxs = kmalloc(i, GFP_KERNEL);
 	if (sbi->s_mb_maxs == NULL) {
 		ret = -ENOMEM;
@@ -2914,7 +2914,8 @@ int ext4_mb_init(struct super_block *sb)
 		offset_incr = offset_incr >> 1;
 		max = max >> 1;
 		i++;
-	} while (i <= sb->s_blocksize_bits + 1);
+	} while (i < MB_NUM_ORDERS(sb));
+
 
 	spin_lock_init(&sbi->s_md_lock);
 	sbi->s_mb_free_pending = 0;

fs/ext4/mballoc.h

@@ -78,6 +78,11 @@
  */
 #define MB_DEFAULT_MAX_INODE_PREALLOC	512
 
+/*
+ * Number of valid buddy orders
+ */
+#define MB_NUM_ORDERS(sb)		((sb)->s_blocksize_bits + 2)
+
 struct ext4_free_data {
 	/* this links the free block information from sb_info */
 	struct list_head		efd_list;