The Dcache

• Contains a hash table of "dentry" objects, each representing a translation from a path to an inode (including "negative" dentries - representing recent lookups to non-existing files).
• The dentries are also connected in a tree structure, representing the structures of files and directories on the mounted file systems.
• An entry remains in the dcache until its file-system is un-mounted...
• ... or until it is pruned during a cache shrink, which happens once every 300 seconds, by the swap-daemon (kswapd)...
• ... or when the swap-daemon (kswapd) needs to free space.
• See file fs/cache.c, function prune_dcache, for the gory details.

Originally written by guy keren