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    SubjectRe: [PATCH 04/41] VFS: Remove unnecessary micro-optimization in cached_lookup()
    In message <1256152779-10054-5-git-send-email-vaurora@redhat.com>, Valerie Aurora writes:
    > From: Jan Blunck <jblunck@suse.de>
    >
    > d_lookup() takes rename_lock which is a seq_lock. This is so cheap
    > it's not worth calling lockless __d_lookup() first from
    > cache_lookup(). Rename cached_lookup() to cache_lookup() while we're
    > there.

    Val, this is another patch unrelated to union mounts, an
    optimization/simplification of the VFS code. I think you need to try and
    push such VFS patches upstream more quickly, so as to reduce the set of UM
    patches you have to maintain.

    > Signed-off-by: Jan Blunck <jblunck@suse.de>
    > Signed-off-by: Valerie Aurora <vaurora@redhat.com>
    > ---
    > fs/namei.c | 13 ++++---------
    > 1 files changed, 4 insertions(+), 9 deletions(-)
    >
    > diff --git a/fs/namei.c b/fs/namei.c
    > index e334f25..9c9ecfa 100644
    > --- a/fs/namei.c
    > +++ b/fs/namei.c
    > @@ -404,15 +404,10 @@ do_revalidate(struct dentry *dentry, struct nameidata *nd)
    > * Internal lookup() using the new generic dcache.
    > * SMP-safe
    > */
    > -static struct dentry * cached_lookup(struct dentry * parent, struct qstr * name, struct nameidata *nd)
    > +static struct dentry *cache_lookup(struct dentry *parent, struct qstr *name,
    > + struct nameidata *nd)
    > {
    > - struct dentry * dentry = __d_lookup(parent, name);
    > -
    > - /* lockess __d_lookup may fail due to concurrent d_move()
    > - * in some unrelated directory, so try with d_lookup
    > - */
    > - if (!dentry)
    > - dentry = d_lookup(parent, name);
    > + struct dentry *dentry = d_lookup(parent, name);
    >
    > if (dentry && dentry->d_op && dentry->d_op->d_revalidate)
    > dentry = do_revalidate(dentry, nd);
    > @@ -1191,7 +1186,7 @@ static struct dentry *__lookup_hash(struct qstr *name,
    > goto out;
    > }
    >
    > - dentry = cached_lookup(base, name, nd);
    > + dentry = cache_lookup(base, name, nd);
    > if (!dentry) {
    > struct dentry *new;
    >
    > --
    > 1.6.3.3
    >
    > --
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    Erez.


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