Commit b3423415 authored Dec 06, 2006 by Eric Dumazet Committed by Linus Torvalds Dec 07, 2006

[PATCH] dcache: avoid RCU for never-hashed dentries



Some dentries don't need to be globally visible in dentry hashtable.
(pipes & sockets)

Such dentries dont need to wait for a RCU grace period at delete time.
Being able to free them permits a better CPU cache use (hot cache)

This patch combined with (dont insert pipe dentries into dentry_hashtable)
reduced time of { pipe(p); close(p[0]); close(p[1]);} on my UP machine (1.6
GHz Pentium-M) from 3.23 us to 2.86 us (But this patch does not depend on
other patches, only bench results)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Maneesh Soni <maneesh@in.ibm.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Acked-by: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent d18de5a2

fs/dcache.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -68,15 +68,19 @@ struct dentry_stat_t dentry_stat = {
		.age_limit = 45,
		};

		static void d_callback(struct rcu_head *head)
		static void __d_free(struct dentry *dentry)
		{
		struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);

		if (dname_external(dentry))
		kfree(dentry->d_name.name);
		kmem_cache_free(dentry_cache, dentry);
		}

		static void d_callback(struct rcu_head *head)
		{
		struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);
		__d_free(dentry);
		}

		/*
		* no dcache_lock, please. The caller must decrement dentry_stat.nr_dentry
		* inside dcache_lock.
		@@ -85,6 +89,10 @@ static void d_free(struct dentry *dentry)
		{
		if (dentry->d_op && dentry->d_op->d_release)
		dentry->d_op->d_release(dentry);
		/* if dentry was never inserted into hash, immediate free is OK */
		if (dentry->d_hash.pprev == NULL)
		__d_free(dentry);
		else
		call_rcu(&dentry->d_u.d_rcu, d_callback);
		}

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