• Eric Dumazet's avatar
    [PATCH] shrink dentry struct · 5160ee6f
    Eric Dumazet authored
    Some long time ago, dentry struct was carefully tuned so that on 32 bits
    UP, sizeof(struct dentry) was exactly 128, ie a power of 2, and a multiple
    of memory cache lines.
    Then RCU was added and dentry struct enlarged by two pointers, with nice
    results for SMP, but not so good on UP, because breaking the above tuning
    (128 + 8 = 136 bytes)
    This patch reverts this unwanted side effect, by using an union (d_u),
    where d_rcu and d_child are placed so that these two fields can share their
    memory needs.
    At the time d_free() is called (and d_rcu is really used), d_child is known
    to be empty and not touched by the dentry freeing.
    Lockless lookups only access d_name, d_parent, d_lock, d_op, d_flags (so
    the previous content of d_child is not needed if said dentry was unhashed
    but still accessed by a CPU because of RCU constraints)
    As dentry cache easily contains millions of entries, a size reduction is
    worth the extra complexity of the ugly C union.
    Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
    Cc: Dipankar Sarma <dipankar@in.ibm.com>
    Cc: Maneesh Soni <maneesh@in.ibm.com>
    Cc: Miklos Szeredi <miklos@szeredi.hu>
    Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
    Cc: Ian Kent <raven@themaw.net>
    Cc: Paul Jackson <pj@sgi.com>
    Cc: Al Viro <viro@ftp.linux.org.uk>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
    Cc: Neil Brown <neilb@cse.unsw.edu.au>
    Cc: James Morris <jmorris@namei.org>
    Cc: Stephen Smalley <sds@epoch.ncsc.mil>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
cpuset.c 64.3 KB