[PATCH v3 03/32] dcache: convert dentry_stat.nr_unused to per-cpu counters

Glauber Costa
2013-04-08T14:00:30Z

From: Dave Chinner <dchinner@redhat.com>

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@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
fs/dcache.c | 24 +++++++++++++++++++++---
1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index fbfae008..ffdd461 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -118,6 +118,14 @@ struct dentry_stat_t dentry_stat = {
};

static DEFINE_PER_CPU(unsigned int, nr_dentry);
+/*
+ * The total counts for nr_dentry_unused are hotplug-safe, since we always loop
+ * through all possible cpus. It is quite possible, though, that the counters
+ * go negative. That could easily happen for a dentry that is marked unused in
+ * one CPU but decrements that count after being preempted to another CPU.
+ * Therefore, we must use a signed quantity in here.
+ */
+static DEFINE_PER_CPU(long , nr_dentry_unused);

#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
static int get_nr_dentry(void)
@@ -129,10 +137,20 @@ 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;
+}
+
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
@@ -312,7 +330,7 @@ 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);
}
}
@@ -322,7 +340,7 @@ static void __dentry_lru_del(struct dentry *dentry)
list_del_init(&dentry->d_lru);
dentry->d_flags &= ~DCACHE_SHRINK_LIST;
dentry->d_sb->s_nr_dentry_unused--;
- dentry_stat.nr_unused--;
+ this_cpu_dec(nr_dentry_unused);
}

/*
@@ -360,7 +378,7 @@ static void dentry_lru_move_list(struct dentry *dentry, struct list_head *list)
if (list_empty(&dentry->d_lru)) {
list_add_tail(&dentry->d_lru, list);
dentry->d_sb->s_nr_dentry_unused++;
- dentry_stat.nr_unused++;
+ this_cpu_inc(nr_dentry_unused);
} else {
list_move_tail(&dentry->d_lru, list);
}
--
1.8.1.4