Commit 61f3dee4 authored by Nick Piggin's avatar Nick Piggin
Browse files

fs: dcache reduce dput locking 



It is possible to run dput without taking data structure locks up-front. In
many cases where we don't kill the dentry anyway, these locks are not required.

Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
parent 58db63d0

fs/dcache.c

+23 −29
Original line number Diff line number Diff line
@@ -323,35 +323,16 @@ void dput(struct dentry *dentry) 
	if (dentry->d_count == 1)

		might_sleep();

	spin_lock(&dentry->d_lock);

	if (IS_ROOT(dentry))

		parent = NULL;

	else

		parent = dentry->d_parent;

	if (dentry->d_count == 1) {

		if (!spin_trylock(&dcache_inode_lock)) {

drop2:

			spin_unlock(&dentry->d_lock);

			goto repeat;

		}

		if (parent && !spin_trylock(&parent->d_lock)) {

			spin_unlock(&dcache_inode_lock);

			goto drop2;

		}

	}

	BUG_ON(!dentry->d_count);

	if (dentry->d_count > 1) {

		dentry->d_count--;

	if (dentry->d_count) {

		spin_unlock(&dentry->d_lock);

		if (parent)

			spin_unlock(&parent->d_lock);

		return;

	}



	/*

	 * AV: ->d_delete() is _NOT_ allowed to block now.

	 */

	if (dentry->d_op && dentry->d_op->d_delete) {

		if (dentry->d_op->d_delete(dentry))

			goto unhash_it;

			goto kill_it;

	}



	/* Unreachable? Get rid of it */
@@ -362,17 +343,30 @@ void dput(struct dentry *dentry) 
	dentry->d_flags |= DCACHE_REFERENCED;

	dentry_lru_add(dentry);



	dentry->d_count--;

	spin_unlock(&dentry->d_lock);

	if (parent)

		spin_unlock(&parent->d_lock);

	spin_unlock(&dcache_inode_lock);

	return;



unhash_it:

	__d_drop(dentry);

kill_it:

	if (!spin_trylock(&dcache_inode_lock)) {

relock:

		spin_unlock(&dentry->d_lock);

		cpu_relax();

		goto repeat;

	}

	if (IS_ROOT(dentry))

		parent = NULL;

	else

		parent = dentry->d_parent;

	if (parent && !spin_trylock(&parent->d_lock)) {

		spin_unlock(&dcache_inode_lock);

		goto relock;

	}

	dentry->d_count--;

	/* if dentry was on the d_lru list delete it from there */

	dentry_lru_del(dentry);

	/* if it was on the hash (d_delete case), then remove it */

	__d_drop(dentry);

	dentry = d_kill(dentry, parent);

	if (dentry)

		goto repeat;