ext4: mballoc: refactor ext4_mb_discard_preallocations()

Implement ext4_mb_discard_preallocations_should_retry()
which we will need in later patches to add more logic
like check for sequence number match to see if we should
retry for block allocation or not.

There should be no functionality change in this patch.
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/1cfae0098d2aa9afbeb59331401258182868c8f2.1589955723.git.riteshh@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -4543,6 +4543,17 @@ static int ext4_mb_discard_preallocations(struct super_block *sb, int needed)
 	return freed;
 }
 
+static bool ext4_mb_discard_preallocations_should_retry(struct super_block *sb,
+			struct ext4_allocation_context *ac)
+{
+	int freed;
+
+	freed = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
+	if (freed)
+		return true;
+	return false;
+}
+
 /*
  * Main entry point into mballoc to allocate blocks
  * it tries to use preallocation first, then falls back
@@ -4551,7 +4562,6 @@ static int ext4_mb_discard_preallocations(struct super_block *sb, int needed)
 ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
 				struct ext4_allocation_request *ar, int *errp)
 {
-	int freed;
 	struct ext4_allocation_context *ac = NULL;
 	struct ext4_sb_info *sbi;
 	struct super_block *sb;
@@ -4656,8 +4666,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
 			ar->len = ac->ac_b_ex.fe_len;
 		}
 	} else {
-		freed  = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
-		if (freed)
+		if (ext4_mb_discard_preallocations_should_retry(sb, ac))
 			goto repeat;
 		/*
 		 * If block allocation fails then the pa allocated above