Before this patch, we were using a very inefficient way to search
chunks:
We iterate through all clusters to find the chunk root tree block first,
then re-iterate all clusters again to find every child tree block.
Each time we need to iterate all clusters just to find a chunk tree
block. This is obviously inefficient, especially when chunk tree gets
larger. So the original author leaves a comment on it:
/* If you have to ask you aren't worthy */
static int search_for_chunk_blocks()
This patch will change the behavior so that we will only iterate all
clusters once.
The idea behind the optimization is, since we have the superblock
restored first, we could use the CHUNK_ITEMs in
super_block::sys_chunk_array to build a SYSTEM chunk mapping.
Then, when we start to iterate through all items, we can easily skip
unrelated items at different level:
- At cluster level
If a cluster starts beyond last system chunk map, it must not contain
any chunk tree blocks (as chunk tree blocks only lives inside system
chunks)
- At item level
If one item has no intersection with any system chunk map, then it
must not contain any tree blocks.
By this, we can iterate through all clusters just once, and find out all
CHUNK_ITEMs.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
1796d5099f