Commit 77812a1e authored by Nick Piggin's avatar Nick Piggin
Browse files

fs: consolidate dentry kill sequence 



The tricky locking for disposing of a dentry is duplicated 3 times in the
dcache (dput, pruning a dentry from the LRU, and pruning its ancestors).
Consolidate them all into a single function dentry_kill.

Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
parent ec33679d

fs/dcache.c

+61 −74
Original line number Diff line number Diff line
@@ -284,6 +284,40 @@ void d_drop(struct dentry *dentry) 
}

EXPORT_SYMBOL(d_drop);



/*

 * Finish off a dentry we've decided to kill.

 * dentry->d_lock must be held, returns with it unlocked.

 * If ref is non-zero, then decrement the refcount too.

 * Returns dentry requiring refcount drop, or NULL if we're done.

 */

static inline struct dentry *dentry_kill(struct dentry *dentry, int ref)

	__releases(dentry->d_lock)

{

	struct dentry *parent;



	if (!spin_trylock(&dcache_inode_lock)) {

relock:

		spin_unlock(&dentry->d_lock);

		cpu_relax();

		return dentry; /* try again with same dentry */

	}

	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;

	}

	if (ref)

		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 then remove it */

	__d_drop(dentry);

	return d_kill(dentry, parent);

}



/* 

 * This is dput

 *
@@ -309,13 +343,9 @@ EXPORT_SYMBOL(d_drop); 
 * call the dentry unlink method as well as removing it from the queues and

 * releasing its resources. If the parent dentries were scheduled for release

 * they too may now get deleted.

 *

 * no dcache lock, please.

 */



void dput(struct dentry *dentry)

{

	struct dentry *parent;

	if (!dentry)

		return;
@@ -348,26 +378,7 @@ void dput(struct dentry *dentry) 
	return;



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);

	dentry = dentry_kill(dentry, 1);

	if (dentry)

		goto repeat;

}
@@ -563,51 +574,43 @@ void d_prune_aliases(struct inode *inode) 
EXPORT_SYMBOL(d_prune_aliases);



/*

 * Throw away a dentry - free the inode, dput the parent.  This requires that

 * the LRU list has already been removed.

 * Try to throw away a dentry - free the inode, dput the parent.

 * Requires dentry->d_lock is held, and dentry->d_count == 0.

 * Releases dentry->d_lock.

 *

 * Try to prune ancestors as well.  This is necessary to prevent

 * quadratic behavior of shrink_dcache_parent(), but is also expected

 * to be beneficial in reducing dentry cache fragmentation.

 * This may fail if locks cannot be acquired no problem, just try again.

 */

static void prune_one_dentry(struct dentry *dentry, struct dentry *parent)

static void try_prune_one_dentry(struct dentry *dentry)

	__releases(dentry->d_lock)

	__releases(parent->d_lock)

	__releases(dcache_inode_lock)

{

	__d_drop(dentry);

	dentry = d_kill(dentry, parent);

	struct dentry *parent;



	parent = dentry_kill(dentry, 0);

	/*

	 * Prune ancestors.

	 * If dentry_kill returns NULL, we have nothing more to do.

	 * if it returns the same dentry, trylocks failed. In either

	 * case, just loop again.

	 *

	 * Otherwise, we need to prune ancestors too. This is necessary

	 * to prevent quadratic behavior of shrink_dcache_parent(), but

	 * is also expected to be beneficial in reducing dentry cache

	 * fragmentation.

	 */

	if (!parent)

		return;

	if (parent == dentry)

		return;



	/* Prune ancestors. */

	dentry = parent;

	while (dentry) {

relock:

		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))

			parent = NULL;

		else

			parent = dentry->d_parent;

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

			spin_unlock(&dcache_inode_lock);

			goto relock2;

		}

		dentry->d_count--;

		dentry_lru_del(dentry);

		__d_drop(dentry);

		dentry = d_kill(dentry, parent);

		dentry = dentry_kill(dentry, 1);

	}

}
@@ -617,8 +620,6 @@ static void shrink_dentry_list(struct list_head *list) 


	rcu_read_lock();

	for (;;) {

		struct dentry *parent;



		dentry = list_entry_rcu(list->prev, struct dentry, d_lru);

		if (&dentry->d_lru == list)

			break; /* empty */
@@ -639,24 +640,10 @@ static void shrink_dentry_list(struct list_head *list) 
			continue;

		}



		if (!spin_trylock(&dcache_inode_lock)) {

relock:

			spin_unlock(&dentry->d_lock);

			cpu_relax();

			continue;

		}

		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_lru_del(dentry);



		rcu_read_unlock();

		prune_one_dentry(dentry, parent);



		try_prune_one_dentry(dentry);



		rcu_read_lock();

	}

	rcu_read_unlock();