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fs: dcache reduce prune_one_dentry locking

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prune_one_dentry can avoid quite a bit of locking in the common case where
ancestors have an elevated refcount. Alternatively, we could have gone the
other way and made fewer trylocks in the case where d_count goes to zero, but
is probably less common.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
This commit is contained in:
Nick Piggin 2011-01-07 17:49:45 +11:00
parent a734eb458a
commit 89e6054836
1 changed files with 15 additions and 12 deletions
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27
fs/dcache.c
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@ -582,26 +582,29 @@ static void prune_one_dentry(struct dentry *dentry, struct dentry *parent)
* Prune ancestors. * Prune ancestors.
*/ */
while (dentry) { while (dentry) {
spin_lock(&dcache_inode_lock); relock:
again:
spin_lock(&dentry->d_lock); spin_lock(&dentry->d_lock);
if (dentry->d_count > 1) {
dentry->d_count--;
spin_unlock(&dentry->d_lock);
return;
}
if (!spin_trylock(&dcache_inode_lock)) {
relock2:
spin_unlock(&dentry->d_lock);
cpu_relax();
goto relock;
}
if (IS_ROOT(dentry)) if (IS_ROOT(dentry))
parent = NULL; parent = NULL;
else else
parent = dentry->d_parent; parent = dentry->d_parent;
if (parent && !spin_trylock(&parent->d_lock)) { if (parent && !spin_trylock(&parent->d_lock)) {
spin_unlock(&dentry->d_lock); spin_unlock(&dcache_inode_lock);
goto again; goto relock2;
} }
dentry->d_count--; dentry->d_count--;
if (dentry->d_count) {
if (parent)
spin_unlock(&parent->d_lock);
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_inode_lock);
return;
}
dentry_lru_del(dentry); dentry_lru_del(dentry);
__d_drop(dentry); __d_drop(dentry);
dentry = d_kill(dentry, parent); dentry = d_kill(dentry, parent);