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dentry_kill(): don't bother with retain_dentry() on slow path

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We have already checked it and dentry used to look not worthy
of keeping.  The only hard obstacle to evicting dentry is
non-zero refcount; everything else is advisory - e.g. memory
pressure could evict any dentry found with refcount zero.
On the slow path in dentry_kill() we had dropped and regained
->d_lock; we must recheck the refcount, but everything else
is not worth bothering with.

Note that filesystem can not count upon ->d_delete() being
called for dentry - not even once.  Again, memory pressure
(as well as d_prune_aliases(), or attempted rmdir() of ancestor,
or...) will not call ->d_delete() at all.

So from the correctness point of view we are fine doing the
check only once.  And it makes things simpler down the road.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2023-10-31 00:23:35 -04:00
parent ee0c82503d
commit b06c684d39
1 changed files with 2 additions and 6 deletions
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8
fs/dcache.c
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@ -739,14 +739,10 @@ static struct dentry *dentry_kill(struct dentry *dentry)
spin_lock(&dentry->d_lock);
parent = lock_parent(dentry);
got_locks:
if (unlikely(dentry->d_lockref.count != 1)) {
dentry->d_lockref.count--;
} else if (likely(!retain_dentry(dentry))) {
dentry->d_lockref.count--;
dentry->d_lockref.count--;
if (likely(dentry->d_lockref.count == 0)) {
__dentry_kill(dentry);
return parent;
} else {
dentry->d_lockref.count--;
}
/* we are keeping it, after all */
if (inode)