Re: [PATCH 1/2] dcache: convert dentry_stat.nr_unused to per-cpu counters

[Pekka Enberg]

On Mon, Aug 8, 2011 at 10:03 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Before we split up the dcache_lru_lock, the unused dentry counter
> needs to be made independent of the global dcache_lru_lock. Convert
> it to per-cpu counters to do this.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
>  fs/dcache.c |   17 ++++++++++++++---
>  1 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index b05aac3..5e5208d 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -116,6 +116,7 @@ struct dentry_stat_t dentry_stat = {
>  };
>
>  static DEFINE_PER_CPU(unsigned int, nr_dentry);
> +static DEFINE_PER_CPU(unsigned int, nr_dentry_unused);
>
>  #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
>  static int get_nr_dentry(void)
> @@ -127,10 +128,20 @@ static int get_nr_dentry(void)
>        return sum < 0 ? 0 : sum;
>  }
>
> +static int get_nr_dentry_unused(void)
> +{
> +       int i;
> +       int sum = 0;
> +       for_each_possible_cpu(i)
> +               sum += per_cpu(nr_dentry_unused, i);
> +       return sum < 0 ? 0 : sum;
> +}

Why not use struct percpu_counter and percpu_counter_sum_positive() for this?

> +
>  int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
>                   size_t *lenp, loff_t *ppos)
>  {
>        dentry_stat.nr_dentry = get_nr_dentry();
> +       dentry_stat.nr_unused = get_nr_dentry_unused();
>        return proc_dointvec(table, write, buffer, lenp, ppos);
>  }
>  #endif
> @@ -233,7 +244,7 @@ static void dentry_lru_add(struct dentry *dentry)
>                spin_lock(&dcache_lru_lock);
>                list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
>                dentry->d_sb->s_nr_dentry_unused++;
> -               dentry_stat.nr_unused++;
> +               this_cpu_inc(nr_dentry_unused);
>                spin_unlock(&dcache_lru_lock);
>        }
>  }
> @@ -242,7 +253,7 @@ static void __dentry_lru_del(struct dentry *dentry)
>  {
>        list_del_init(&dentry->d_lru);
>        dentry->d_sb->s_nr_dentry_unused--;
> -       dentry_stat.nr_unused--;
> +       this_cpu_dec(nr_dentry_unused);
>  }
>
>  static void dentry_lru_del(struct dentry *dentry)
> @@ -260,7 +271,7 @@ static void dentry_lru_move_tail(struct dentry *dentry)
>        if (list_empty(&dentry->d_lru)) {
>                list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
>                dentry->d_sb->s_nr_dentry_unused++;
> -               dentry_stat.nr_unused++;
> +               this_cpu_inc(nr_dentry_unused);
>        } else {
>                list_move_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
>        }
> --
> 1.7.5.4
>
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