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    SubjectRe: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
    Miklos Szeredi <miklos@szeredi.hu> writes:

    > On Sat, Feb 15, 2014 at 01:39:22PM -0800, Eric W. Biederman wrote:
    >>
    >> Now that d_invalidate is the only caller of check_submounts_and_drop,
    >> expand check_submounts_and_drop inline in d_invalidate.
    >>
    >> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    >> ---
    >> fs/dcache.c | 55 +++++++++++++++++++----------------------------
    >> include/linux/dcache.h | 1 -
    >> 2 files changed, 22 insertions(+), 34 deletions(-)
    >>
    >> diff --git a/fs/dcache.c b/fs/dcache.c
    >> index 27585b1dd6f1..5b41205cbf33 100644
    >> --- a/fs/dcache.c
    >> +++ b/fs/dcache.c

    >> -int check_submounts_and_drop(struct dentry *dentry)
    >> +int d_invalidate(struct dentry *dentry)
    >> {
    >> int ret = 0;
    >>
    >> + /*
    >> + * If it's already been dropped, return OK.
    >> + */
    >> + spin_lock(&dentry->d_lock);
    >> + if (d_unhashed(dentry)) {
    >> + spin_unlock(&dentry->d_lock);
    >> + return 0;
    >> + }
    >> + spin_unlock(&dentry->d_lock);
    >> +
    >> /* Negative dentries can be dropped without further checks */
    >> if (!dentry->d_inode) {
    >> d_drop(dentry);
    >
    >
    > You can optimize this by including the negative check within the above d_locked
    > region and calling __d_drop() instead.

    For this patch just moving the code and not changing it is the corret
    thing to do because it helps with review and understanding the code.

    There are two ways I could see going with optimizing the preamble.
    Simply dropping the d_lock from around the d_unhashed test as a pointer
    dereference should be atomic, and the test is racy against
    d_materialise_unique. (We don't always hold the parent
    directories inode mutex when d_invalidate is called). So the d_lock
    buys us very little. Alternatively we could move the work into the
    d_walk callbacks.

    That kind of optimization deserves it's own patch that can be reviewed
    independently.

    Eric


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