ceph: move to a dedicated slabcache for ceph_cap_snap

There could be huge number of capsnaps around at any given time. On
x86_64 the structure is 248 bytes, which will be rounded up to 256 bytes
by kzalloc. Move this to a dedicated slabcache to save 8 bytes for each.

[ jlayton: use kmem_cache_zalloc ]
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/snap.c

@@ -482,7 +482,7 @@ static void ceph_queue_cap_snap(struct ceph_inode_info *ci)
 	struct ceph_buffer *old_blob = NULL;
 	int used, dirty;
 
-	capsnap = kzalloc(sizeof(*capsnap), GFP_NOFS);
+	capsnap = kmem_cache_zalloc(ceph_cap_snap_cachep, GFP_NOFS);
 	if (!capsnap) {
 		pr_err("ENOMEM allocating ceph_cap_snap on %p\n", inode);
 		return;
@@ -603,7 +603,8 @@ static void ceph_queue_cap_snap(struct ceph_inode_info *ci)
 	spin_unlock(&ci->i_ceph_lock);
 
 	ceph_buffer_put(old_blob);
-	kfree(capsnap);
+	if (capsnap)
+		kmem_cache_free(ceph_cap_snap_cachep, capsnap);
 	ceph_put_snap_context(old_snapc);
 }
 

fs/ceph/super.c

@@ -864,6 +864,7 @@ static void destroy_fs_client(struct ceph_fs_client *fsc)
  */
 struct kmem_cache *ceph_inode_cachep;
 struct kmem_cache *ceph_cap_cachep;
+struct kmem_cache *ceph_cap_snap_cachep;
 struct kmem_cache *ceph_cap_flush_cachep;
 struct kmem_cache *ceph_dentry_cachep;
 struct kmem_cache *ceph_file_cachep;
@@ -892,6 +893,9 @@ static int __init init_caches(void)
 	ceph_cap_cachep = KMEM_CACHE(ceph_cap, SLAB_MEM_SPREAD);
 	if (!ceph_cap_cachep)
 		goto bad_cap;
+	ceph_cap_snap_cachep = KMEM_CACHE(ceph_cap_snap, SLAB_MEM_SPREAD);
+	if (!ceph_cap_snap_cachep)
+		goto bad_cap_snap;
 	ceph_cap_flush_cachep = KMEM_CACHE(ceph_cap_flush,
 					   SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD);
 	if (!ceph_cap_flush_cachep)
@@ -931,6 +935,8 @@ static int __init init_caches(void)
 bad_dentry:
 	kmem_cache_destroy(ceph_cap_flush_cachep);
 bad_cap_flush:
+	kmem_cache_destroy(ceph_cap_snap_cachep);
+bad_cap_snap:
 	kmem_cache_destroy(ceph_cap_cachep);
 bad_cap:
 	kmem_cache_destroy(ceph_inode_cachep);
@@ -947,6 +953,7 @@ static void destroy_caches(void)
 
 	kmem_cache_destroy(ceph_inode_cachep);
 	kmem_cache_destroy(ceph_cap_cachep);
+	kmem_cache_destroy(ceph_cap_snap_cachep);
 	kmem_cache_destroy(ceph_cap_flush_cachep);
 	kmem_cache_destroy(ceph_dentry_cachep);
 	kmem_cache_destroy(ceph_file_cachep);

fs/ceph/super.h

@@ -230,7 +230,7 @@ static inline void ceph_put_cap_snap(struct ceph_cap_snap *capsnap)
 	if (refcount_dec_and_test(&capsnap->nref)) {
 		if (capsnap->xattr_blob)
 			ceph_buffer_put(capsnap->xattr_blob);
-		kfree(capsnap);
+		kmem_cache_free(ceph_cap_snap_cachep, capsnap);
 	}
 }
 

include/linux/ceph/libceph.h

@@ -284,6 +284,7 @@ DEFINE_RB_LOOKUP_FUNC(name, type, keyfld, nodefld)
 
 extern struct kmem_cache *ceph_inode_cachep;
 extern struct kmem_cache *ceph_cap_cachep;
+extern struct kmem_cache *ceph_cap_snap_cachep;
 extern struct kmem_cache *ceph_cap_flush_cachep;
 extern struct kmem_cache *ceph_dentry_cachep;
 extern struct kmem_cache *ceph_file_cachep;