[PATCH] f2fs: reduce lock overhead of extent node releasing

[Chao Yu]

Open and close critical section for each extent node when traversing rb-tree
results in high overhead of cpu, slows thing down.

This patch alternates to batch mode for removing extent nodes under spin lock.

Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx>
---
 fs/f2fs/data.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 6a706dd..7fb56a0 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -441,19 +441,31 @@ static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
 	struct extent_node *en;
 	unsigned int count = et->count;
 
-	node = rb_first(&et->root);
-	while (node) {
-		next = rb_next(node);
-		en = rb_entry(node, struct extent_node, rb_node);
+	if (!et->count)
+		return 0;
+
+	/* 1. remove all extent nodes in global lru list */
+	if (free_all) {
+		spin_lock(&sbi->extent_lock);
+		node = rb_first(&et->root);
+		while (node) {
+			next = rb_next(node);
+			en = rb_entry(node, struct extent_node, rb_node);
 
-		if (free_all) {
-			spin_lock(&sbi->extent_lock);
 			if (!list_empty(&en->list))
 				list_del_init(&en->list);
-			spin_unlock(&sbi->extent_lock);
+			node = next;
 		}
+		spin_unlock(&sbi->extent_lock);
+	}
+
+	/* 2. release all extent nodes which are not in global lru list */
+	node = rb_first(&et->root);
+	while (node) {
+		next = rb_next(node);
+		en = rb_entry(node, struct extent_node, rb_node);
 
-		if (free_all || list_empty(&en->list)) {
+		if (list_empty(&en->list)) {
 			__detach_extent_node(sbi, et, en);
 			kmem_cache_free(extent_node_slab, en);
 		}
-- 
2.4.2

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