Commit b3423415 authored by Eric Dumazet's avatar Eric Dumazet Committed by Linus Torvalds
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[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: default avatarEric Dumazet <>
Cc: Al Viro <>
Cc: Maneesh Soni <>
Cc: "Paul E. McKenney" <>
Cc: Dipankar Sarma <>
Acked-by: default avatarDavid Miller <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent d18de5a2
......@@ -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))
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);
* no dcache_lock, please. The caller must decrement dentry_stat.nr_dentry
* inside dcache_lock.
......@@ -85,7 +89,11 @@ static void d_free(struct dentry *dentry)
if (dentry->d_op && dentry->d_op->d_release)
call_rcu(&dentry->d_u.d_rcu, d_callback);
/* if dentry was never inserted into hash, immediate free is OK */
if (dentry->d_hash.pprev == NULL)
call_rcu(&dentry->d_u.d_rcu, d_callback);
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