reduce m_start() cost...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 18 insertions, 3 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 65233a5f390a..a66aff5bd3fe 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -52,7 +52,7 @@ static int __init set_mphash_entries(char *str)
 }
 __setup("mphash_entries=", set_mphash_entries);
 
-static int event;
+static u64 event;
 static DEFINE_IDA(mnt_id_ida);
 static DEFINE_IDA(mnt_group_ida);
 static DEFINE_SPINLOCK(mnt_id_lock);
@@ -1100,14 +1100,29 @@ static void *m_start(struct seq_file *m, loff_t *pos)
         struct proc_mounts *p = proc_mounts(m);
 
         down_read(&namespace_sem);
-        return seq_list_start(&p->ns->list, *pos);
+        if (p->cached_event == p->ns->event) {
+                void *v = p->cached_mount;
+                if (*pos == p->cached_index)
+                        return v;
+                if (*pos == p->cached_index + 1) {
+                        v = seq_list_next(v, &p->ns->list, &p->cached_index);
+                        return p->cached_mount = v;
+                }
+        }
+
+        p->cached_event = p->ns->event;
+        p->cached_mount = seq_list_start(&p->ns->list, *pos);
+        p->cached_index = *pos;
+        return p->cached_mount;
 }
 
 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
 {
         struct proc_mounts *p = proc_mounts(m);
 
-        return seq_list_next(v, &p->ns->list, pos);
+        p->cached_mount = seq_list_next(v, &p->ns->list, pos);
+        p->cached_index = *pos;
+        return p->cached_mount;
 }
 
 static void m_stop(struct seq_file *m, void *v)