On Fri, May 11, 2018 at 11:09:37AM -0700, evan.g.thomp...@gmail.com wrote: > From: Evan Thompson <evan.thomp...@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.thomp...@flukenetworks.com>
Reviewed-by: Tom Rini <tr...@konsulko.com> -- Tom
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