[Devel] [PATCH RHEL7 COMMIT] tcache: speedup tcaches operations on empty tcache

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.36.1.vz7.20.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.36.1.vz7.20.14
------>
commit 851cef04ceb68f61f95e03314e8008afb75b8113
Author: Andrey Ryabinin <aryabinin at virtuozzo.com>
Date:   Tue Dec 13 16:48:12 2016 +0400

    tcache: speedup tcaches operations on empty tcache
    
    If tcache is empty we can bail out immediately from
    tcache_cleancache_[get_page, invalidate_page,invalidate_inode]().
    As a fast way of identifying empty tcache this patch adds global atomic
    counter of tcache nodes.
    
    https://jira.sw.ru/browse/PSBM-56475
    
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
    Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 mm/tcache.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/mm/tcache.c b/mm/tcache.c
index cec5a4e..c7613b2 100644
--- a/mm/tcache.c
+++ b/mm/tcache.c
@@ -98,6 +98,8 @@ struct tcache_pool {
 	struct tcache_pool_nodeinfo	nodeinfo[0];
 };
 
+static atomic_long_t nr_tcache_nodes;
+
 /*
  * Tcache nodes correspond to inodes. A node is created automatically when a
  * new page is added to the cache (cleancache_put_page) and destroyed either
@@ -561,6 +563,7 @@ retry:
 		node->pool = pool;
 		node->key = *key;
 		atomic_long_inc(&pool->nr_nodes);
+		atomic_long_inc(&nr_tcache_nodes);
 		__tcache_insert_node(&tree->root, node, rb_link, rb_parent);
 	}
 	spin_unlock_irqrestore(&tree->lock, flags);
@@ -590,6 +593,7 @@ static void tcache_node_release_fn(struct kref *kref)
 	__tcache_delete_node(&tree->root, node);
 	spin_unlock(&tree->lock);
 
+	atomic_long_dec(&nr_tcache_nodes);
 	atomic_long_dec(&node->pool->nr_nodes);
 	kfree(node);
 }
@@ -1168,6 +1172,9 @@ static int tcache_cleancache_get_page(int pool_id,
 	struct tcache_node *node;
 	struct page *cache_page = NULL;
 
+	if (!atomic_long_read(&nr_tcache_nodes))
+		return -1;
+
 	node = tcache_get_node_and_pool(pool_id, &key, false);
 	if (node) {
 		cache_page = tcache_detach_page(node, index, true);
@@ -1192,6 +1199,9 @@ static void tcache_cleancache_invalidate_page(int pool_id,
 	struct tcache_node *node;
 	struct page *page;
 
+	if (!atomic_long_read(&nr_tcache_nodes))
+		return;
+
 	node = tcache_get_node_and_pool(pool_id, &key, false);
 	if (node) {
 		page = tcache_detach_page(node, index, false);
@@ -1206,6 +1216,9 @@ static void tcache_cleancache_invalidate_inode(int pool_id,
 {
 	struct tcache_pool *pool;
 
+	if (!atomic_long_read(&nr_tcache_nodes))
+		return;
+
 	pool = tcache_get_pool(pool_id);
 	if (pool) {
 		tcache_invalidate_node(pool, &key);