Le vendredi 05 août 2011 à 04:35 +0400, Glauber Costa a écrit :
> Now that we have per-sb shrinkers, it makes sense to have nr_dentries
> stored per sb as well. We turn them into per-cpu counters so we can
> keep acessing them without locking.
>
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> CC: Dave Chinner <david@xxxxxxxxxxxxx>
> ---
> fs/dcache.c | 12 +++++++++++-
> fs/super.c | 15 ++++++++++++++-
> include/linux/fs.h | 2 ++
> 3 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index b05aac3..ac19d24 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -151,7 +151,13 @@ static void __d_free(struct rcu_head *head)
> static void d_free(struct dentry *dentry)
> {
> BUG_ON(dentry->d_count);
> + /*
> + * It is cheaper to keep a global counter separate
> + * then to scan through all superblocks when needed
"then to scan" or "than scanning" ?
> + */
> this_cpu_dec(nr_dentry);
> + this_cpu_dec(*dentry->d_sb->s_nr_dentry);
> +
> if (dentry->d_op && dentry->d_op->d_release)
> dentry->d_op->d_release(dentry);
>
> @@ -1224,7 +1230,11 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
> INIT_LIST_HEAD(&dentry->d_alias);
> INIT_LIST_HEAD(&dentry->d_u.d_child);
> d_set_d_op(dentry, dentry->d_sb->s_d_op);
> -
> + /*
> + * It is cheaper to keep a global counter separate
> + * then to scan through all superblocks when needed
> + */
> + this_cpu_inc(*dentry->d_sb->s_nr_dentry);
> this_cpu_inc(nr_dentry);
>
> return dentry;
> diff --git a/fs/super.c b/fs/super.c
> index 3f56a26..9345385 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -112,6 +112,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
> {
> struct super_block *s = kzalloc(sizeof(struct super_block), GFP_USER);
> static const struct super_operations default_op;
> + int i;
>
> if (s) {
> if (security_sb_alloc(s)) {
> @@ -119,15 +120,26 @@ static struct super_block *alloc_super(struct file_system_type *type)
> s = NULL;
> goto out;
> }
> +
> + s->s_nr_dentry = alloc_percpu(int);
> + if (!s->s_nr_dentry) {
> + security_sb_free(s);
> + kfree(s);
> + s = NULL;
> + goto out;
> + }
> + for_each_possible_cpu(i)
> + *per_cpu_ptr(s->s_nr_dentry, i) = 0;
This loop is not needed, alloc_percpu() gives zeroed data
Why dont you use a percpu_counter ?
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