[PATCH 1/3] ext4: Teach ext4_meta_trans_blocks() about number of allocated extents

[Jan Kara <jack@suse.cz>]

So far ext4_meta_trans_blocks() expects that each extent counted in
@pextents will be allocated in the transaction we estimate credits for.
This is correct for the use in ext4_chunk_trans_blocks() and
ext4_chunk_trans_extent() however the use in atomic write path
(ext4_convert_unwritten_extents_atomic() and ext4_iomap_alloc() for
IOMAP_ATOMIC) unnecessarily overestimates the number of necessary
credits as neither of them allocates any data. Add argument to
ext4_meta_trans_blocks() for number of extents that are going to be
allocated in the transaction.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/ext4.h    |  2 +-
 fs/ext4/extents.c |  2 +-
 fs/ext4/inode.c   | 32 +++++++++++++++++---------------
 3 files changed, 19 insertions(+), 17 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index b37c136ea3ab..6e0cc9b845ae 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3184,7 +3184,7 @@ extern int ext4_normal_submit_inode_data_buffers(struct jbd2_inode *jinode);
 extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
 extern int ext4_chunk_trans_extent(struct inode *inode, int nrblocks);
 extern int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
-				  int pextents);
+				  int pextents, int alloc_extents);
 extern int ext4_block_zero_eof(struct inode *inode, loff_t from, loff_t end);
 extern int ext4_zero_partial_blocks(struct inode *inode, loff_t lstart,
 				    loff_t length, bool *did_zero);
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 91c97af64b31..44ab246a3176 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4976,7 +4976,7 @@ int ext4_convert_unwritten_extents_atomic(handle_t *handle, struct inode *inode,
 		 * it can tell if the extent in the cache is a split extent.
 		 * But for now let's assume pextents as 2 always.
 		 */
-		credits = ext4_meta_trans_blocks(inode, max_blocks, 2);
+		credits = ext4_meta_trans_blocks(inode, max_blocks, 2, 0);
 	}
 
 	if (credits) {
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ce99807c5f5b..f324a54f1dae 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3693,9 +3693,11 @@ static int ext4_iomap_alloc(struct inode *inode, struct ext4_map_blocks *map,
 		if (ret < 0)
 			return ret;
 		if (map->m_len < orig_mlen) {
+			int bpg = EXT4_BLOCKS_PER_GROUP(inode->i_sb);
+
 			map->m_len = orig_mlen;
-			dio_credits = ext4_meta_trans_blocks(inode, orig_mlen,
-							     map->m_len);
+			dio_credits = ext4_meta_trans_blocks(inode, map->m_len,
+							     map->m_len, 0);
 		} else {
 			dio_credits = ext4_chunk_trans_blocks(inode,
 							      map->m_len);
@@ -6307,17 +6309,17 @@ static int ext4_index_trans_blocks(struct inode *inode, int lblocks,
 }
 
 /*
- * Account for index blocks, block groups bitmaps and block group
- * descriptor blocks if modify datablocks and index blocks
- * worse case, the indexs blocks spread over different block groups
- *
- * If datablocks are discontiguous, they are possible to spread over
- * different block groups too. If they are contiguous, with flexbg,
- * they could still across block group boundary.
- *
- * Also account for superblock, inode, quota and xattr blocks
+ * Calculate number of credits needed in a transaction to:
+ *   * Allocate data blocks from @alloc_extents different groups - note that
+ *     with flexbg a single physical extent can span multiple groups but
+ *     single mballoc request only returns extent within one group.
+ *   * Allocate metatadata (extent tree blocks, indirect blocks) to store
+ *     pointers to @pextents data extents having @lblocks in total.
+ *   * Modify extent tree / indirect block tree, inode, superblock, quota
+ *     tracking, xattr blocks
  */
-int ext4_meta_trans_blocks(struct inode *inode, int lblocks, int pextents)
+int ext4_meta_trans_blocks(struct inode *inode, int lblocks, int pextents,
+			   int alloc_extents)
 {
 	ext4_group_t groups, ngroups = ext4_get_groups_count(inode->i_sb);
 	int gdpblocks;
@@ -6334,7 +6336,7 @@ int ext4_meta_trans_blocks(struct inode *inode, int lblocks, int pextents)
 	 * Now let's see how many group bitmaps and group descriptors need
 	 * to account
 	 */
-	groups = idxblocks + pextents;
+	groups = idxblocks + alloc_extents;
 	gdpblocks = groups;
 	if (groups > ngroups)
 		groups = ngroups;
@@ -6360,7 +6362,7 @@ int ext4_chunk_trans_extent(struct inode *inode, int nrblocks)
 {
 	int ret;
 
-	ret = ext4_meta_trans_blocks(inode, nrblocks, 1);
+	ret = ext4_meta_trans_blocks(inode, nrblocks, 1, 1);
 	/* Account for data blocks for journalled mode */
 	if (ext4_should_journal_data(inode))
 		ret += nrblocks;
@@ -6378,7 +6380,7 @@ int ext4_chunk_trans_extent(struct inode *inode, int nrblocks)
  */
 int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
 {
-	return ext4_meta_trans_blocks(inode, nrblocks, 1);
+	return ext4_meta_trans_blocks(inode, nrblocks, 1, 1);
 }
 
 /*
-- 
2.51.0