Btrfs: fix data allocation hint start (6346c939) · Commits · 戴 / test

Sometimes our start allocation hint when we cow a file can be either EXTENT_HOLE or some other such place holder, which is not optimal. So if we find that our em->block_start is one of these special values, check to see where the first block of the inode is stored, and use that as a hint. If that block is also a special value, just fallback on a hint of 0 and let the allocator figure out a good place to put the data. Signed-off-by:

Josef Bacik <josef@redhat.com> Signed-off-by:

Chris Mason <chris.mason@oracle.com>

fs/btrfs/inode.c

+16 −2

Original line number	Diff line number	Diff line
		@@ -743,9 +743,23 @@ static noinline int cow_file_range(struct inode *inode,
		em = search_extent_mapping(&BTRFS_I(inode)->extent_tree,
		start, num_bytes);
		if (em) {
		/*
		* if block start isn't an actual block number then find the
		* first block in this inode and use that as a hint. If that
		* block is also bogus then just don't worry about it.
		*/
		if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
		free_extent_map(em);
		em = search_extent_mapping(em_tree, 0, 0);
		if (em && em->block_start < EXTENT_MAP_LAST_BYTE)
		alloc_hint = em->block_start;
		if (em)
		free_extent_map(em);
		} else {
		alloc_hint = em->block_start;
		free_extent_map(em);
		}
		}
		read_unlock(&BTRFS_I(inode)->extent_tree.lock);
		btrfs_drop_extent_cache(inode, start, start + num_bytes - 1, 0);

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