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Commit b3423415fbc2e5461605826317da1c8dbbf21f97

Authored by Eric Dumazet
Committed by Linus Torvalds
1 parent d18de5a272
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

[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>

Showing 1 changed file with 12 additions and 4 deletions Side-by-side Diff

... ... @@ -68,15 +68,19 @@
68 68 .age_limit = 45,
69 69 };
70 70  
71   -static void d_callback(struct rcu_head *head)
  71 +static void __d_free(struct dentry *dentry)
72 72 {
73   - struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);
74   -
75 73 if (dname_external(dentry))
76 74 kfree(dentry->d_name.name);
77 75 kmem_cache_free(dentry_cache, dentry);
78 76 }
79 77  
  78 +static void d_callback(struct rcu_head *head)
  79 +{
  80 + struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);
  81 + __d_free(dentry);
  82 +}
  83 +
80 84 /*
81 85 * no dcache_lock, please. The caller must decrement dentry_stat.nr_dentry
82 86 * inside dcache_lock.
... ... @@ -85,7 +89,11 @@
85 89 {
86 90 if (dentry->d_op && dentry->d_op->d_release)
87 91 dentry->d_op->d_release(dentry);
88   - call_rcu(&dentry->d_u.d_rcu, d_callback);
  92 + /* if dentry was never inserted into hash, immediate free is OK */
  93 + if (dentry->d_hash.pprev == NULL)
  94 + __d_free(dentry);
  95 + else
  96 + call_rcu(&dentry->d_u.d_rcu, d_callback);
89 97 }
90 98  
91 99 /*