On Fri, May 11, 2018 at 11:09:37AM -0700, evan.g.thompson@gmail.com wrote:
From: Evan Thompson evan.thompson@flukenetworks.com
In ext4, the file inode can store up to 4 extents. If a file requires more (due to size or fragmentation), an extent index tree is used.
Currently, u-boot reads a node from each level of the extent tree for every block read, which is very inefficient when extent tree depth is > 0.
This patch adds a cache for the extent tree. We cache the 1 most-recently-seen node at each extent tree level. The typical workload is sequential block access, so once we leave a given tree node, it will not be revisited. Therefore, it makes sense to just cache one node per tree level.
Cached blocks are lazily allocated. The typical case is extent tree depth = 0, in which case no caching is needed and no allocations will occur.
For files with extent tree depth = 1, this patch produces a ~10x improvement in read speed. For deeper extent trees, the improvement is larger. On my test device, a 3MB file which previously took 9s to read now takes 150ms.
Cache size is configurable with CONFIG_EXT4_EXTENT_CACHE_SIZE. However the default of 5 (the maximum depth of well-formed extent trees) is recommended.
Signed-off-by: Evan Thompson evan.thompson@flukenetworks.com
Reviewed-by: Tom Rini trini@konsulko.com