From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:39524 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751971AbeERDAl (ORCPT ); Thu, 17 May 2018 23:00:41 -0400 From: Liu Bo To: Subject: [PATCH v2 5/6] Btrfs: grab write lock directly if write_lock_level is the max level Date: Fri, 18 May 2018 11:00:23 +0800 Message-Id: <1526612424-97061-6-git-send-email-bo.liu@linux.alibaba.com> In-Reply-To: <1526612424-97061-1-git-send-email-bo.liu@linux.alibaba.com> References: <1526612424-97061-1-git-send-email-bo.liu@linux.alibaba.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: Typically, when acquiring root node's lock, btrfs tries its best to get read lock and trade for write lock if @write_lock_level implies to do so. In case of (cow && (p->keep_locks || p->lowest_level)), write_lock_level is set to BTRFS_MAX_LEVEL, which means we need to acquire root node's write lock directly. In this particular case, the dance of acquiring read lock and then trading for write lock can be saved. Signed-off-by: Liu Bo --- fs/btrfs/ctree.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-) diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 8d3b09038f37..e619f7e01794 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -2633,20 +2633,23 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root, goto out; } - /* - * we don't know the level of the root node until we actually - * have it read locked - */ - b = btrfs_read_lock_root_node(root); - level = btrfs_header_level(b); - if (level > write_lock_level) - goto out; + if (write_lock_level < BTRFS_MAX_LEVEL) { + /* + * we don't know the level of the root node until we actually + * have it read locked + */ + b = btrfs_read_lock_root_node(root); + level = btrfs_header_level(b); + if (level > write_lock_level) + goto out; + + /* + * whoops, must trade for write lock + */ + btrfs_tree_read_unlock(b); + free_extent_buffer(b); + } - /* - * whoops, must trade for write lock - */ - btrfs_tree_read_unlock(b); - free_extent_buffer(b); b = btrfs_lock_root_node(root); root_lock = BTRFS_WRITE_LOCK; /* -- 1.8.3.1