On Mon, Mar 26, 2018 at 04:05:24PM -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
doc/README.ext4 | 7 +++++ fs/ext4/ext4_common.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 76 insertions(+), 5 deletions(-)
diff --git a/doc/README.ext4 b/doc/README.ext4 index 8ecd21eee3..a501b92396 100644 --- a/doc/README.ext4 +++ b/doc/README.ext4 @@ -33,6 +33,13 @@ In addition, to get the write access command "ext4write", enable: which automatically selects CONFIG_EXT4_WRITE if it wasn't defined already.
+For files with extents, an ext4 extent tree cache improves performance:
- CONFIG_EXT4_EXTENT_CACHE_SIZE <#>
+The above cache size defaults to 5 if not defined. This default is +strongly recommended. 0 will turn off extent caching.
Also relevant are the generic filesystem commands, selected by:
CONFIG_CMD_FS_GENERIC diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c index e3cc30a1e0..61aade1ced 100644 --- a/fs/ext4/ext4_common.c +++ b/fs/ext4/ext4_common.c @@ -1523,6 +1523,47 @@ void ext4fs_allocate_blocks(struct ext2_inode *file_inode,
#endif
+/* Extent tree cache caches one entry per tree level
- eg, ext_block->eh_depth is used as the index into the cache
- If the tree is deeper than CONFIG_EXT4_EXTENT_CACHE_SIZE (very unlikely),
- file read performance will be impacted by repeated re-reads
- of those index nodes.
- */
+#ifndef CONFIG_EXT4_EXTENT_CACHE_SIZE +#define CONFIG_EXT4_EXTENT_CACHE_SIZE 5 +#endif
This needs to be done in Kconfig. Also, is there any sort of testing we could add to test/fs/fs-test.sh for this code? Thanks!