ceph: optimizing cap reservation

When caps_avail_count is in a low level, most newly
trimmed caps will probably go into ->caps_list and
caps_avail_count will be increased. Hence after trimming,
should recheck caps_avail_count to effectly reuse
newly trimmed caps. Also, when releasing unnecessary
caps follow the same rule of ceph_put_cap.

Signed-off-by: Chengguang Xu <cgxu519@icloud.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index b9b5c47..25141b6 100644 (file)
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -184,36 +184,54 @@ int ceph_reserve_caps(struct ceph_mds_client *mdsc,
                                         mdsc->caps_avail_count);
        spin_unlock(&mdsc->caps_list_lock);
 
-       for (i = have; i < need; i++) {
-retry:
+       for (i = have; i < need; ) {
                cap = kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);
-               if (!cap) {
-                       if (!trimmed) {
-                               for (j = 0; j < mdsc->max_sessions; j++) {
-                                       s = __ceph_lookup_mds_session(mdsc, j);
-                                       if (!s)
-                                               continue;
-                                       mutex_unlock(&mdsc->mutex);
+               if (cap) {
+                       list_add(&cap->caps_item, &newcaps);
+                       alloc++;
+                       i++;
+                       continue;
+               }
 
-                                       mutex_lock(&s->s_mutex);
-                                       max_caps = s->s_nr_caps - (need - i);
-                                       ceph_trim_caps(mdsc, s, max_caps);
-                                       mutex_unlock(&s->s_mutex);
+               if (!trimmed) {
+                       for (j = 0; j < mdsc->max_sessions; j++) {
+                               s = __ceph_lookup_mds_session(mdsc, j);
+                               if (!s)
+                                       continue;
+                               mutex_unlock(&mdsc->mutex);
 
-                                       ceph_put_mds_session(s);
-                                       mutex_lock(&mdsc->mutex);
-                               }
-                               trimmed = true;
-                               goto retry;
-                       } else {
-                               pr_warn("reserve caps ctx=%p ENOMEM "
-                                       "need=%d got=%d\n",
-                                       ctx, need, have + alloc);
-                               goto out_nomem;
+                               mutex_lock(&s->s_mutex);
+                               max_caps = s->s_nr_caps - (need - i);
+                               ceph_trim_caps(mdsc, s, max_caps);
+                               mutex_unlock(&s->s_mutex);
+
+                               ceph_put_mds_session(s);
+                               mutex_lock(&mdsc->mutex);
                        }
+                       trimmed = true;
+
+                       spin_lock(&mdsc->caps_list_lock);
+                       if (mdsc->caps_avail_count) {
+                               int more_have;
+                               if (mdsc->caps_avail_count >= need - i)
+                                       more_have = need - i;
+                               else
+                                       more_have = mdsc->caps_avail_count;
+
+                               i += more_have;
+                               have += more_have;
+                               mdsc->caps_avail_count -= more_have;
+                               mdsc->caps_reserve_count += more_have;
+
+                       }
+                       spin_unlock(&mdsc->caps_list_lock);
+
+                       continue;
                }
-               list_add(&cap->caps_item, &newcaps);
-               alloc++;
+
+               pr_warn("reserve caps ctx=%p ENOMEM need=%d got=%d\n",
+                       ctx, need, have + alloc);
+               goto out_nomem;
        }
        BUG_ON(have + alloc != need);
 
@@ -234,16 +252,28 @@ retry:
        return 0;
 
 out_nomem:
+
+       spin_lock(&mdsc->caps_list_lock);
+       mdsc->caps_avail_count += have;
+       mdsc->caps_reserve_count -= have;
+
        while (!list_empty(&newcaps)) {
                cap = list_first_entry(&newcaps,
                                struct ceph_cap, caps_item);
                list_del(&cap->caps_item);
-               kmem_cache_free(ceph_cap_cachep, cap);
+
+               /* Keep some preallocated caps around (ceph_min_count), to
+                * avoid lots of free/alloc churn. */
+               if (mdsc->caps_avail_count >=
+                   mdsc->caps_reserve_count + mdsc->caps_min_count) {
+                       kmem_cache_free(ceph_cap_cachep, cap);
+               } else {
+                       mdsc->caps_avail_count++;
+                       mdsc->caps_total_count++;
+                       list_add(&cap->caps_item, &mdsc->caps_list);
+               }
        }
 
-       spin_lock(&mdsc->caps_list_lock);
-       mdsc->caps_avail_count += have;
-       mdsc->caps_reserve_count -= have;
        BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
                                         mdsc->caps_reserve_count +
                                         mdsc->caps_avail_count);