Alex Tomas wrote:
Good day,
please review ...
thanks, Alex
Basic delayed allocation in ext4
Two special ->get_block() methods are introduced:
* ext4_da_get_block_prep()
to be used with ->prepare_write(), defers allocation till flush
* ext4_da_get_block_write()
to be used with mpage_da_writepages(), allocate blocks and correct
on-disk size
Current implementation works with data=writeback only, you should
mount filesystem with delalloc,data=writeback options.
TODO:
* reservation
* data=ordered
* quota
* bmap
Signed-off-by: Alex Tomas <alex@xxxxxxxxxxxxx>
[.. snip...]
/*
* Test whether an inode is a fast symlink.
*/
@@ -1291,6 +1293,142 @@ static int ext4_journalled_commit_write(
}
/*
+ * this is a special callback for ->prepare_write() 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,
+ struct buffer_head *bh_result, int create)
+{
+ int ret = 0;
+
+ 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 */
+ ret = ext4_get_blocks_wrap(NULL, inode, iblock, 1, bh_result, 0, 0);
+ if (ret >= 0) {
I guess this should be (ret > 0)
+ if (buffer_mapped(bh_result)) {
+ bh_result->b_size = (ret << inode->i_blkbits);
+ } else {
+ /* OK, the block isn't allocated yet, let's reserve space */
+ /* XXX: call reservation here */
[...snip..]
epare_write(struct file *file, struct page *page,
+ unsigned from, unsigned to)
+{
+ return block_prepare_write(page, from, to, ext4_da_get_block_prep);
+}
+
+ return ret;
+}
+
+static int ext4_da_writepages(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ return mpage_da_writepages(mapping, wbc, ext4_da_get_block_write);
+}
I was not able to find mpage_da_writepages()..
-aneesh
-
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