From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759295Ab0KPO0M (ORCPT ); Tue, 16 Nov 2010 09:26:12 -0500 Received: from ipmail05.adl6.internode.on.net ([150.101.137.143]:2280 "EHLO ipmail05.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758641Ab0KPOYB (ORCPT ); Tue, 16 Nov 2010 09:24:01 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AogKAKMh4kx5Ldur/2dsb2JhbACUX4ECjH1yvmaFSwSKWIUQ Message-Id: <20101116142030.612454500@kernel.dk> User-Agent: quilt/0.48-1 Date: Wed, 17 Nov 2010 01:09:25 +1100 From: Nick Piggin To: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Subject: [patch 25/28] fs: dcache reduce prune_one_dentry locking References: <20101116140900.039761100@kernel.dk> Content-Disposition: inline; filename=dcache-prune_one_dentry-less-lock.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org prune_one_dentry can avoid quite a bit of locking in the common case where ancestors have an elevated refcount. Alternatively, we could have gone the other way and made fewer trylocks in the case where d_count goes to zero, but is probably less common. Signed-off-by: Nick Piggin --- fs/dcache.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) Index: linux-2.6/fs/dcache.c =================================================================== --- linux-2.6.orig/fs/dcache.c 2010-11-17 00:52:38.000000000 +1100 +++ linux-2.6/fs/dcache.c 2010-11-17 01:05:38.000000000 +1100 @@ -547,26 +547,29 @@ static void prune_one_dentry(struct dent * Prune ancestors. */ while (dentry) { - spin_lock(&dcache_inode_lock); -again: +relock: spin_lock(&dentry->d_lock); + if (dentry->d_count > 1) { + dentry->d_count--; + spin_unlock(&dentry->d_lock); + return; + } + if (!spin_trylock(&dcache_inode_lock)) { +relock2: + spin_unlock(&dentry->d_lock); + cpu_relax(); + goto relock; + } + if (IS_ROOT(dentry)) parent = NULL; else parent = dentry->d_parent; if (parent && !spin_trylock(&parent->d_lock)) { - spin_unlock(&dentry->d_lock); - goto again; - } - dentry->d_count--; - if (dentry->d_count) { - if (parent) - spin_unlock(&parent->d_lock); - spin_unlock(&dentry->d_lock); spin_unlock(&dcache_inode_lock); - return; + goto relock2; } - + dentry->d_count--; dentry_lru_del(dentry); __d_drop(dentry); dentry = d_kill(dentry, parent);