From patchwork Thu Oct 29 19:07:48 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Davidlohr Bueso X-Patchwork-Id: 11867267 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0E4E0697 for ; Thu, 29 Oct 2020 19:29:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E570C207EA for ; Thu, 29 Oct 2020 19:29:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726148AbgJ2T3l (ORCPT ); Thu, 29 Oct 2020 15:29:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:51804 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726120AbgJ2T3d (ORCPT ); Thu, 29 Oct 2020 15:29:33 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 26D71AE72; Thu, 29 Oct 2020 19:28:42 +0000 (UTC) Date: Thu, 29 Oct 2020 12:07:48 -0700 From: Davidlohr Bueso To: Dave Chinner Cc: viro@zeniv.linux.org.uk, akpm@linux-foundation.org, peterz@infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Davidlohr Bueso Subject: [PATCH v2] fs/dcache: optimize start_dir_add() Message-ID: <20201029190748.u5zrnk6rjtc4p43v@linux-p48b> References: <20201022211650.25045-1-dave@stgolabs.net> <20201026215923.GA306023@dread.disaster.area> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201026215923.GA306023@dread.disaster.area> User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Considering both end_dir_add() and d_alloc_parallel(), the dir->i_dir_seq wants acquire/release semantics, therefore micro-optimize for ll/sc archs. Also add READ_ONCE around the variable mostly for documentation purposes - either the successful cmpxchg or the pause will avoid the tearing). Signed-off-by: Davidlohr Bueso --- fs/dcache.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 2.26.2 diff --git a/fs/dcache.c b/fs/dcache.c index ea0485861d93..9177f0d08a5a 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2504,8 +2504,8 @@ static inline unsigned start_dir_add(struct inode *dir) { for (;;) { - unsigned n = dir->i_dir_seq; - if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n) + unsigned n = READ_ONCE(dir->i_dir_seq); + if (!(n & 1) && cmpxchg_acquire(&dir->i_dir_seq, n, n + 1) == n) return n; cpu_relax(); }