From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Layton Subject: [PATCH v4 08/14] locks: avoid taking global lock if possible when waking up blocked waiters Date: Fri, 21 Jun 2013 08:58:16 -0400 Message-ID: <1371819502-26363-9-git-send-email-jlayton@redhat.com> References: <1371819502-26363-1-git-send-email-jlayton@redhat.com> Cc: linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, cluster-devel@redhat.com, sage@inktank.com, samba-technical@lists.samba.org, Trond.Myklebust@netapp.com, linux-kernel@vger.kernel.org, piastryyy@gmail.com, linux-afs@lists.infradead.org, dhowells@redhat.com, smfrench@gmail.com, linux-fsdevel@vger.kernel.org, ceph-devel@vger.kernel.org, akpm@linux-foundation.org To: viro@zeniv.linux.org.uk, matthew@wil.cx, bfields@fieldses.org Return-path: In-Reply-To: <1371819502-26363-1-git-send-email-jlayton@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: cluster-devel-bounces@redhat.com Errors-To: cluster-devel-bounces@redhat.com List-Id: linux-fsdevel.vger.kernel.org Since we always hold the i_lock when inserting a new waiter onto the fl_block list, we can avoid taking the global lock at all if we find that it's empty when we go to wake up blocked waiters. Signed-off-by: Jeff Layton --- fs/locks.c | 15 ++++++++++++++- 1 files changed, 14 insertions(+), 1 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index ce302d4..84e269f 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -548,7 +548,10 @@ static void locks_delete_block(struct file_lock *waiter) * the order they blocked. The documentation doesn't require this but * it seems like the reasonable thing to do. * - * Must be called with file_lock_lock held! + * Must be called with both the i_lock and file_lock_lock held. The fl_block + * list itself is protected by the file_lock_list, but by ensuring that the + * i_lock is also held on insertions we can avoid taking the file_lock_lock + * in some cases when we see that the fl_block list is empty. */ static void __locks_insert_block(struct file_lock *blocker, struct file_lock *waiter) @@ -576,6 +579,16 @@ static void locks_insert_block(struct file_lock *blocker, */ static void locks_wake_up_blocks(struct file_lock *blocker) { + /* + * Avoid taking global lock if list is empty. This is safe since new + * blocked requests are only added to the list under the i_lock, and + * the i_lock is always held here. Note that removal from the fl_block + * list does not require the i_lock, so we must recheck list_empty() + * after acquiring the file_lock_lock. + */ + if (list_empty(&blocker->fl_block)) + return; + spin_lock(&file_lock_lock); while (!list_empty(&blocker->fl_block)) { struct file_lock *waiter; -- 1.7.1