ext4: journal credits reservation fixes for DIO, fallocate

DIO and fallocate credit calculation is different than writepage, as
they do start a new journal right for each call to ext4_get_blocks_wrap().
This patch uses the helper function in DIO and fallocate case, passing
a flag indicating that the modified data are contigous thus could account
less indirect/index blocks.

This patch also fixed the journal credit reservation for direct I/O
(DIO).  Previously the estimated credits for DIO only was calculated for
non-extent files, which was not enough if the file is extent-based.

Also fixed was fallocate double-counting credits for modifying the the
superblock.

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

3 files changed, 30 insertions, 27 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 38e661b0ea88..295003241d3d 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1073,6 +1073,7 @@ extern void ext4_get_inode_flags(struct ext4_inode_info *);
 extern void ext4_set_aops(struct inode *inode);
 extern int ext4_writepage_trans_blocks(struct inode *);
 extern int ext4_meta_trans_blocks(struct inode *, int nrblocks, int idxblocks);
+extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
 extern int ext4_block_truncate_page(handle_t *handle,
                 struct address_space *mapping, loff_t from);
 extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 5c5dd3a1d657..5596b70efa20 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1758,7 +1758,7 @@ int ext4_ext_calc_credits_for_single_extent(struct inode *inode, int num,
 {
         if (path) {
                 int depth = ext_depth(inode);
-                int ret;
+                int ret = 0;
 
                 /* probably there is space in leaf? */
                 if (le16_to_cpu(path[depth].p_hdr->eh_entries)
@@ -1777,7 +1777,7 @@ int ext4_ext_calc_credits_for_single_extent(struct inode *inode, int num,
                 }
         }
 
-        return ext4_meta_trans_blocks(inode, num, 1);
+        return ext4_chunk_trans_blocks(inode, num);
 }
 
 /*
@@ -2810,7 +2810,7 @@ void ext4_ext_truncate(struct inode *inode)
         /*
          * probably first extent we're gonna free will be last in block
          */
-        err = ext4_writepage_trans_blocks(inode) + 3;
+        err = ext4_writepage_trans_blocks(inode);
         handle = ext4_journal_start(inode, err);
         if (IS_ERR(handle))
                 return;
@@ -2923,10 +2923,9 @@ long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
         max_blocks = (EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits)
                                                         - block;
         /*
-         * credits to insert 1 extent into extent tree + buffers to be able to
-         * modify 1 super block, 1 block bitmap and 1 group descriptor.
+         * credits to insert 1 extent into extent tree
          */
-        credits = EXT4_DATA_TRANS_BLOCKS(inode->i_sb) + 3;
+        credits = ext4_chunk_trans_blocks(inode, max_blocks);
         mutex_lock(&inode->i_mutex);
 retry:
         while (ret >= 0 && ret < max_blocks) {
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a27129065144..ffc95ba48859 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1044,18 +1044,6 @@ static void ext4_da_update_reserve_space(struct inode *inode, int used)
         spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
 }
 
-/* Maximum number of blocks we map for direct IO at once. */
-#define DIO_MAX_BLOCKS 4096
-/*
- * Number of credits we need for writing DIO_MAX_BLOCKS:
- * We need sb + group descriptor + bitmap + inode -> 4
- * For B blocks with A block pointers per block we need:
- * 1 (triple ind.) + (B/A/A + 2) (doubly ind.) + (B/A + 2) (indirect).
- * If we plug in 4096 for B and 256 for A (for 1KB block size), we get 25.
- */
-#define DIO_CREDITS 25
-
-
 /*
  * The ext4_get_blocks_wrap() function try to look up the requested blocks,
  * and returns if the blocks are already mapped.
@@ -1167,19 +1155,23 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
         return retval;
 }
 
+/* Maximum number of blocks we map for direct IO at once. */
+#define DIO_MAX_BLOCKS 4096
+
 static int ext4_get_block(struct inode *inode, sector_t iblock,
                         struct buffer_head *bh_result, int create)
 {
         handle_t *handle = ext4_journal_current_handle();
         int ret = 0, started = 0;
         unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
+        int dio_credits;
 
         if (create && !handle) {
                 /* Direct IO write... */
                 if (max_blocks > DIO_MAX_BLOCKS)
                         max_blocks = DIO_MAX_BLOCKS;
-                handle = ext4_journal_start(inode, DIO_CREDITS +
-                              2 * EXT4_QUOTA_TRANS_BLOCKS(inode->i_sb));
+                dio_credits = ext4_chunk_trans_blocks(inode, max_blocks);
+                handle = ext4_journal_start(inode, dio_credits);
                 if (IS_ERR(handle)) {
                         ret = PTR_ERR(handle);
                         goto out;
@@ -2243,7 +2235,7 @@ static int ext4_da_writepage(struct page *page,
  * for DIO, writepages, and truncate
  */
 #define EXT4_MAX_WRITEBACK_PAGES      DIO_MAX_BLOCKS
-#define EXT4_MAX_WRITEBACK_CREDITS    DIO_CREDITS
+#define EXT4_MAX_WRITEBACK_CREDITS    25
 
 static int ext4_da_writepages(struct address_space *mapping,
                                 struct writeback_control *wbc)
@@ -4441,7 +4433,8 @@ int ext4_meta_trans_blocks(struct inode *inode, int nrblocks, int chunk)
 
 /*
  * Calulate the total number of credits to reserve to fit
- * the modification of a single pages into a single transaction
+ * the modification of a single pages into a single transaction,
+ * which may include multiple chunks of block allocations.
  *
  * This could be called via ext4_write_begin() or later
  * ext4_da_writepages() in delalyed allocation case.
@@ -4449,11 +4442,6 @@ int ext4_meta_trans_blocks(struct inode *inode, int nrblocks, int chunk)
  * In both case it's possible that we could allocating multiple
  * chunks of blocks. We need to consider the worse case, when
  * one new block per extent.
- *
- * For Direct IO and fallocate, the journal credits reservation
- * is based on one single extent allocation, so they could use
- * EXT4_DATA_TRANS_BLOCKS to get the needed credit to log a single
- * chunk of allocation needs.
  */
 int ext4_writepage_trans_blocks(struct inode *inode)
 {
@@ -4467,6 +4455,21 @@ int ext4_writepage_trans_blocks(struct inode *inode)
                 ret += bpp;
         return ret;
 }
+
+/*
+ * Calculate the journal credits for a chunk of data modification.
+ *
+ * This is called from DIO, fallocate or whoever calling
+ * ext4_get_blocks_wrap() to map/allocate a chunk of contigous disk blocks.
+ *
+ * journal buffers for data blocks are not included here, as DIO
+ * and fallocate do no need to journal data buffers.
+ */
+int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
+{
+        return ext4_meta_trans_blocks(inode, nrblocks, 1);
+}
+
 /*
  * The caller must have previously called ext4_reserve_inode_write().
  * Give this, we know that the caller already has write access to iloc->bh.