ext4: factor out ext4_mb_scan_group()

Extract ext4_mb_scan_group() to make the code clearer and to
prepare for the later conversion of 'choose group' to 'scan groups'.
No functional changes.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250714130327.1830534-15-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: LiBaokun96

fs/ext4/mballoc.c

@@ -2845,12 +2845,56 @@ void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
 	}
 }
 
+static int ext4_mb_scan_group(struct ext4_allocation_context *ac,
+			      ext4_group_t group)
+{
+	int ret;
+	struct super_block *sb = ac->ac_sb;
+	enum criteria cr = ac->ac_criteria;
+
+	ext4_mb_might_prefetch(ac, group);
+
+	/* prevent unnecessary buddy loading. */
+	if (cr < CR_ANY_FREE && spin_is_locked(ext4_group_lock_ptr(sb, group)))
+		return 0;
+
+	/* This now checks without needing the buddy page */
+	ret = ext4_mb_good_group_nolock(ac, group, cr);
+	if (ret <= 0) {
+		if (!ac->ac_first_err)
+			ac->ac_first_err = ret;
+		return 0;
+	}
+
+	ret = ext4_mb_load_buddy(sb, group, ac->ac_e4b);
+	if (ret)
+		return ret;
+
+	/* skip busy group */
+	if (cr >= CR_ANY_FREE)
+		ext4_lock_group(sb, group);
+	else if (!ext4_try_lock_group(sb, group))
+		goto out_unload;
+
+	/* We need to check again after locking the block group. */
+	if (unlikely(!ext4_mb_good_group(ac, group, cr)))
+		goto out_unlock;
+
+	__ext4_mb_scan_group(ac);
+
+out_unlock:
+	ext4_unlock_group(sb, group);
+out_unload:
+	ext4_mb_unload_buddy(ac->ac_e4b);
+	return ret;
+}
+
 static noinline_for_stack int
 ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 {
 	ext4_group_t ngroups, group, i;
 	enum criteria new_cr, cr = CR_GOAL_LEN_FAST;
-	int err = 0, first_err = 0;
+	int err = 0;
 	struct ext4_sb_info *sbi;
 	struct super_block *sb;
 	struct ext4_buddy e4b;
@@ -2912,6 +2956,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 
 	ac->ac_e4b = &e4b;
 	ac->ac_prefetch_ios = 0;
+	ac->ac_first_err = 0;
 repeat:
 	for (; cr < EXT4_MB_NUM_CRS && ac->ac_status == AC_STATUS_CONTINUE; cr++) {
 		ac->ac_criteria = cr;
@@ -2926,57 +2971,17 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 
 		for (i = 0, new_cr = cr; i < ngroups; i++,
 		     ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups)) {
-			int ret = 0;
 
 			cond_resched();
 			if (new_cr != cr) {
 				cr = new_cr;
 				goto repeat;
 			}
 
-			ext4_mb_might_prefetch(ac, group);
-
-			/* prevent unnecessary buddy loading. */
-			if (cr < CR_ANY_FREE &&
-			    spin_is_locked(ext4_group_lock_ptr(sb, group)))
-				continue;
-
-			/* This now checks without needing the buddy page */
-			ret = ext4_mb_good_group_nolock(ac, group, cr);
-			if (ret <= 0) {
-				if (!first_err)
-					first_err = ret;
-				continue;
-			}
-
-			err = ext4_mb_load_buddy(sb, group, &e4b);
+			err = ext4_mb_scan_group(ac, group);
 			if (err)
 				goto out;
 
-			/* skip busy group */
-			if (cr >= CR_ANY_FREE) {
-				ext4_lock_group(sb, group);
-			} else if (!ext4_try_lock_group(sb, group)) {
-				ext4_mb_unload_buddy(&e4b);
-				continue;
-			}
-
-			/*
-			 * We need to check again after locking the
-			 * block group
-			 */
-			ret = ext4_mb_good_group(ac, group, cr);
-			if (ret == 0) {
-				ext4_unlock_group(sb, group);
-				ext4_mb_unload_buddy(&e4b);
-				continue;
-			}
-
-			__ext4_mb_scan_group(ac);
-
-			ext4_unlock_group(sb, group);
-			ext4_mb_unload_buddy(&e4b);
-
 			if (ac->ac_status != AC_STATUS_CONTINUE)
 				break;
 		}
@@ -3025,8 +3030,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 			atomic_inc(&sbi->s_bal_stream_goals);
 	}
 out:
-	if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
-		err = first_err;
+	if (!err && ac->ac_status != AC_STATUS_FOUND && ac->ac_first_err)
+		err = ac->ac_first_err;
 
 	mb_debug(sb, "Best len %d, origin len %d, ac_status %u, ac_flags 0x%x, cr %d ret %d\n",
 		 ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status,

fs/ext4/mballoc.h

@@ -196,6 +196,8 @@ struct ext4_allocation_context {
 	unsigned int ac_prefetch_ios;
 	unsigned int ac_prefetch_nr;
 
+	int ac_first_err;
+
 	__u32 ac_flags;		/* allocation hints */
 	__u32 ac_groups_linear_remaining;
 	__u16 ac_groups_scanned;