[PATCH 3/6 V2 ]Ext4: journal credits reservation fixes for DIO, fallocate

[Mingming Cao <cmm@us.ibm.com>]

Ext4: journal credits reservation fixes for DIO, fallocate

From: Mingming Cao <cmm@us.ibm.com>

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>
---
---
 fs/ext4/ext4.h    |    1 +
 fs/ext4/extents.c |   14 +++++++-------
 fs/ext4/inode.c   |   45 ++++++++++++++++++++++++---------------------
 3 files changed, 32 insertions(+), 28 deletions(-)

===================================================================
Index: linux-2.6.27-rc3/fs/ext4/extents.c
===================================================================
--- linux-2.6.27-rc3.orig/fs/ext4/extents.c	2008-08-15 14:51:07.000000000 -0700
+++ linux-2.6.27-rc3/fs/ext4/extents.c	2008-08-15 17:22:02.000000000 -0700
@@ -1758,7 +1758,7 @@ int ext4_ext_calc_credits_for_single_ext
 {
 	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)
@@ -1771,14 +1771,15 @@ int ext4_ext_calc_credits_for_single_ext
 			 *  bitmaps and block group descriptor blocks
 			 *  and other metadat blocks still need to be
 			 *  accounted.
+			 */
 			ret = (num + EXT4_BLOCKS_PER_GROUP(inode->i_sb) -1)
                              /EXT4_BLOCKS_PER_GROUP(inode->i_sb);
 			/* 1 one bitmap, 1 block group descriptor */
-			ret = ret*2  + EXT4_META_TRANS_BLOCKS(inode->i_sb);
+			ret = ret* 2  + EXT4_META_TRANS_BLOCKS(inode->i_sb);
 		}
 	}
 
-	return ext4_meta_trans_blocks(inode, num, 1);
+	return ext4_chunk_trans_blocks(inode, num);
 }
 
 /*
@@ -2811,7 +2812,7 @@ void ext4_ext_truncate(struct inode *ino
 	/*
 	 * 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;
@@ -2924,10 +2925,9 @@ long ext4_fallocate(struct inode *inode,
 	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) {
Index: linux-2.6.27-rc3/fs/ext4/inode.c
===================================================================
--- linux-2.6.27-rc3.orig/fs/ext4/inode.c	2008-08-15 14:43:20.000000000 -0700
+++ linux-2.6.27-rc3/fs/ext4/inode.c	2008-08-15 17:21:04.000000000 -0700
@@ -1044,18 +1044,6 @@ static void ext4_da_update_reserve_space
 	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 *handl
 	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
  * 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)
@@ -4442,7 +4434,8 @@ int ext4_meta_trans_blocks(struct inode*
 
 /*
  * 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 multile chunk of block allocations.
  *
  * This could be called via ext4_write_begin() or later
  * ext4_da_writepages() in delalyed allocation case.
@@ -4450,11 +4443,6 @@ int ext4_meta_trans_blocks(struct inode*
  * 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)
 {
@@ -4468,6 +4456,21 @@ int ext4_writepage_trans_blocks(struct i
 		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.
Index: linux-2.6.27-rc3/fs/ext4/ext4.h
===================================================================
--- linux-2.6.27-rc3.orig/fs/ext4/ext4.h	2008-08-15 14:43:20.000000000 -0700
+++ linux-2.6.27-rc3/fs/ext4/ext4.h	2008-08-15 14:51:20.000000000 -0700
@@ -1073,6 +1073,7 @@ extern void ext4_get_inode_flags(struct 
 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);