• Eric Nelson's avatar
    drivers: block: add block device cache · e40cf34a
    Eric Nelson authored
    Add a block device cache to speed up repeated reads of block devices by
    various filesystems.
    
    This small amount of cache can dramatically speed up filesystem
    operations by skipping repeated reads of common areas of a block
    device (typically directory structures).
    
    This has shown to have some benefit on FAT filesystem operations of
    loading a kernel and RAM disk, but more dramatic benefits on ext4
    filesystems when the kernel and/or RAM disk are spread across
    multiple extent header structures as described in commit fc0fc50f.
    
    The cache is implemented through a minimal list (block_cache) maintained
    in most-recently-used order and count of the current number of entries
    (cache_count). It uses a maximum block count setting to prevent copies
    of large block reads and an upper bound on the number of cached areas.
    
    The maximum number of entries in the cache defaults to 32 and the maximum
    number of blocks per cache entry has a default of 2, which has shown to
    produce the best results on testing of ext4 and FAT filesystems.
    
    The 'blkcache' command (enabled through CONFIG_CMD_BLOCK_CACHE) allows
    changing these values and can be used to tune for a particular filesystem
    layout.
    Signed-off-by: default avatarEric Nelson <eric@nelint.com>
    e40cf34a
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