ext4: Handling preallocated blocks in delayed allocation
From: Mingming Cao <cmm@xxxxxxxxxx>
This patch fix ext4 delayed allocation that allows it
avoid doing delayed allocation handling for blocks that
are already preallocated on disk.
With delayed allocation, at write_begin() time,
ext4_get_blocks_wrap() now is only doing block map with create = 0.
ext4_get_blocks_wrap() returns 0 if the blocks are not allocated
or preallocated().
If the blocks are prea-allocated, the resulting buffer head
is not mapped marked, but ext4_get_blocks_wrap() returns the number of
blocks are actually being preallocated.
Right now delayed allocation mistream pre-allocated blocks as
un-allocated as the buffer head is unmapped.
This patch fix this by checking the number of blocks
returned by ext4_get_blocks_wrap() rather than checking
if buffer head is mapped or not.
Signed-off-by: Mingming Cao <cmm@xxxxxxxxxx>
---
fs/ext4/inode.c | 36 ++++++++++++++++++------------------
1 file changed, 18 insertions(+), 18 deletions(-)
Index: linux-2.6.25-rc3/fs/ext4/inode.c
===================================================================
--- linux-2.6.25-rc3.orig/fs/ext4/inode.c 2008-02-29 10:17:21.000000000 -0800
+++ linux-2.6.25-rc3/fs/ext4/inode.c 2008-02-29 10:40:01.000000000 -0800
@@ -1343,7 +1343,7 @@ static int ext4_journalled_write_end(str
}
/*
- * this is a special callback for ->prepare_write() only
+ * this is a special callback for ->write_begin() only
* it's intention is to return mapped block or reserve space
*/
static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
@@ -1354,24 +1354,24 @@ static int ext4_da_get_block_prep(struct
BUG_ON(create == 0);
BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
- /* first, we need to know whether the block is allocated already
- * XXX: when the filesystem has a lot of free blocks, we could
- * reserve even allocated blocks to save this lookup */
+ /*
+ * first, we need to know whether the block is allocated already
+ * preallocated blocks are unmapped but should treated
+ * the same as allocated blocks.
+ */
ret = ext4_get_blocks_wrap(NULL, inode, iblock, 1, bh_result, 0, 0);
- if (ret >= 0) {
- if (buffer_mapped(bh_result)) {
- bh_result->b_size = (ret << inode->i_blkbits);
- } else {
- /* the block isn't allocated yet, let's reserve space */
- /* XXX: call reservation here */
- /*
- * XXX: __block_prepare_write() unmaps passed block,
- * is it OK?
- */
- map_bh(bh_result, inode->i_sb, 0);
- set_buffer_new(bh_result);
- set_buffer_delay(bh_result);
- }
+ if (ret == 0) {
+ /* the block isn't allocated yet, let's reserve space */
+ /* XXX: call reservation here */
+ /*
+ * XXX: __block_prepare_write() unmaps passed block,
+ * is it OK?
+ */
+ map_bh(bh_result, inode->i_sb, 0);
+ set_buffer_new(bh_result);
+ set_buffer_delay(bh_result);
+ } else if (ret > 0) {
+ bh_result->b_size = (ret << inode->i_blkbits);
ret = 0;
}
--
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