From 550dce01dd606c88a837138aa448ccd367fb0cbb Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 29 May 2016 20:13:30 -0400 Subject: [PATCH] unify dentry_iput() and dentry_unlink_inode() There is a lot of duplication between dentry_unlink_inode() and dentry_iput(). The only real difference is that dentry_unlink_inode() bumps ->d_seq and dentry_iput() doesn't. The argument of the latter is known to have been unhashed, so anybody who might've found it in RCU lookup would already be doomed to a ->d_seq mismatch. And we want to avoid pointless smp_rmb() there. This patch makes dentry_unlink_inode() bump ->d_seq only for hashed dentries. It's safe (d_delete() calls that sucker only if we are holding the only reference to dentry, so rehash is not going to happen) and it allows to use dentry_unlink_inode() in __dentry_kill() and get rid of dentry_iput(). The interesting question here is profiling; it *is* a hot path, and extra conditional jumps in there might or might not be painful. Signed-off-by: Al Viro --- fs/dcache.c | 45 ++++++++++----------------------------------- 1 file changed, 10 insertions(+), 35 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index f9c63c108881..fe7cde2f2fe5 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -335,44 +335,21 @@ static inline void dentry_rcuwalk_invalidate(struct dentry *dentry) /* * Release the dentry's inode, using the filesystem - * d_iput() operation if defined. Dentry has no refcount - * and is unhashed. - */ -static void dentry_iput(struct dentry * dentry) - __releases(dentry->d_lock) - __releases(dentry->d_inode->i_lock) -{ - struct inode *inode = dentry->d_inode; - if (inode) { - __d_clear_type_and_inode(dentry); - hlist_del_init(&dentry->d_u.d_alias); - spin_unlock(&dentry->d_lock); - spin_unlock(&inode->i_lock); - if (!inode->i_nlink) - fsnotify_inoderemove(inode); - if (dentry->d_op && dentry->d_op->d_iput) - dentry->d_op->d_iput(dentry, inode); - else - iput(inode); - } else { - spin_unlock(&dentry->d_lock); - } -} - -/* - * Release the dentry's inode, using the filesystem - * d_iput() operation if defined. dentry remains in-use. + * d_iput() operation if defined. */ static void dentry_unlink_inode(struct dentry * dentry) __releases(dentry->d_lock) __releases(dentry->d_inode->i_lock) { struct inode *inode = dentry->d_inode; + bool hashed = !d_unhashed(dentry); - raw_write_seqcount_begin(&dentry->d_seq); + if (hashed) + raw_write_seqcount_begin(&dentry->d_seq); __d_clear_type_and_inode(dentry); hlist_del_init(&dentry->d_u.d_alias); - raw_write_seqcount_end(&dentry->d_seq); + if (hashed) + raw_write_seqcount_end(&dentry->d_seq); spin_unlock(&dentry->d_lock); spin_unlock(&inode->i_lock); if (!inode->i_nlink) @@ -540,12 +517,10 @@ static void __dentry_kill(struct dentry *dentry) dentry->d_flags |= DCACHE_DENTRY_KILLED; if (parent) spin_unlock(&parent->d_lock); - dentry_iput(dentry); - /* - * dentry_iput drops the locks, at which point nobody (except - * transient RCU lookups) can reach this dentry. - */ - BUG_ON(dentry->d_lockref.count > 0); + if (dentry->d_inode) + dentry_unlink_inode(dentry); + else + spin_unlock(&dentry->d_lock); this_cpu_dec(nr_dentry); if (dentry->d_op && dentry->d_op->d_release) dentry->d_op->d_release(dentry); -- 2.20.1