f2fs: extent cache: support unaligned extent

Compressed inode may suffer read performance issue due to it can not
use extent cache, so I propose to add this unaligned extent support
to improve it.

Currently, it only works in readonly format f2fs image.

Unaligned extent: in one compressed cluster, physical block number
will be less than logical block number, so we add an extra physical
block length in extent info in order to indicate such extent status.

The idea is if one whole cluster blocks are contiguous physically,
once its mapping info was readed at first time, we will cache an
unaligned (or aligned) extent info entry in extent cache, it expects
that the mapping info will be hitted when rereading cluster.

Merge policy:
- Aligned extents can be merged.
- Aligned extent and unaligned extent can not be merged.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 455561826c7d..7dbfd6965b97 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1666,6 +1666,30 @@ void f2fs_put_page_dic(struct page *page)
 	f2fs_put_dic(dic);
 }
 
+/*
+ * check whether cluster blocks are contiguous, and add extent cache entry
+ * only if cluster blocks are logically and physically contiguous.
+ */
+unsigned int f2fs_cluster_blocks_are_contiguous(struct dnode_of_data *dn)
+{
+	bool compressed = f2fs_data_blkaddr(dn) == COMPRESS_ADDR;
+	int i = compressed ? 1 : 0;
+	block_t first_blkaddr = data_blkaddr(dn->inode, dn->node_page,
+						dn->ofs_in_node + i);
+
+	for (i += 1; i < F2FS_I(dn->inode)->i_cluster_size; i++) {
+		block_t blkaddr = data_blkaddr(dn->inode, dn->node_page,
+						dn->ofs_in_node + i);
+
+		if (!__is_valid_data_blkaddr(blkaddr))
+			break;
+		if (first_blkaddr + i - (compressed ? 1 : 0) != blkaddr)
+			return 0;
+	}
+
+	return compressed ? i - 1 : i;
+}
+
 const struct address_space_operations f2fs_compress_aops = {
 	.releasepage = f2fs_release_page,
 	.invalidatepage = f2fs_invalidate_page,