From: Chengguang Xu <cgxu519@icloud.com>
Date: Sat, 24 Feb 2018 18:35:29 +0800
Subject: ceph: optimizing cap allocation
Git-commit: e327ce068518e38c0182739e879b9dce477c8d85
Patch-mainline: v4.17-rc1
References: bsc#1089115

When setting high volume of caps_min_count or having many
unreserved caps, unused caps may always keep in the ->caps_list
even can't get new cap from kmem_cache_alloc because lack of
maximum limitation of caps_avail_count. Hence reuse caps in
->caps_list if available, it's maybe better than setting max
limitation of caps_avail_count and releasing unused caps when
reaching the limit.

Signed-off-by: Chengguang Xu <cgxu519@icloud.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Acked-by: Luis Henriques <lhenriques@suse.com>
---
 fs/ceph/caps.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -284,7 +284,23 @@ struct ceph_cap *ceph_get_cap(struct cep
 			mdsc->caps_use_count++;
 			mdsc->caps_total_count++;
 			spin_unlock(&mdsc->caps_list_lock);
+		} else {
+			spin_lock(&mdsc->caps_list_lock);
+			if (mdsc->caps_avail_count) {
+				BUG_ON(list_empty(&mdsc->caps_list));
+
+				mdsc->caps_avail_count--;
+				mdsc->caps_use_count++;
+				cap = list_first_entry(&mdsc->caps_list,
+						struct ceph_cap, caps_item);
+				list_del(&cap->caps_item);
+
+				BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
+				       mdsc->caps_reserve_count + mdsc->caps_avail_count);
+			}
+			spin_unlock(&mdsc->caps_list_lock);
 		}
+
 		return cap;
 	}