From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 747AFC00A89 for ; Thu, 5 Nov 2020 10:55:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 159BE21D81 for ; Thu, 5 Nov 2020 10:55:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730018AbgKEKzQ (ORCPT ); Thu, 5 Nov 2020 05:55:16 -0500 Received: from mail.cn.fujitsu.com ([183.91.158.132]:23755 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726777AbgKEKzP (ORCPT ); Thu, 5 Nov 2020 05:55:15 -0500 X-IronPort-AV: E=Sophos;i="5.77,453,1596470400"; d="scan'208";a="100980844" Received: from unknown (HELO cn.fujitsu.com) ([10.167.33.5]) by heian.cn.fujitsu.com with ESMTP; 05 Nov 2020 18:55:11 +0800 Received: from G08CNEXMBPEKD04.g08.fujitsu.local (unknown [10.167.33.201]) by cn.fujitsu.com (Postfix) with ESMTP id C21544CE38B0; Thu, 5 Nov 2020 18:55:06 +0800 (CST) Received: from [10.167.225.206] (10.167.225.206) by G08CNEXMBPEKD04.g08.fujitsu.local (10.167.33.201) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 5 Nov 2020 18:55:06 +0800 Subject: Re: [PATCH v2] fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set To: Jan Kara , Al Viro CC: , , , , , References: <20200924055958.825515-1-lihao2018.fnst@cn.fujitsu.com> <20200924145856.GB3361@quack2.suse.cz> <20201021135133.GA25702@quack2.suse.cz> From: "Li, Hao" Message-ID: <053ff976-8d75-b249-2bba-3a8b7a98b1a4@cn.fujitsu.com> Date: Thu, 5 Nov 2020 18:54:49 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 MIME-Version: 1.0 In-Reply-To: <20201021135133.GA25702@quack2.suse.cz> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.167.225.206] X-ClientProxiedBy: G08CNEXCHPEKD06.g08.fujitsu.local (10.167.33.205) To G08CNEXMBPEKD04.g08.fujitsu.local (10.167.33.201) X-yoursite-MailScanner-ID: C21544CE38B0.ABBE8 X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: lihao2018.fnst@cn.fujitsu.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ping :) On 2020/10/21 21:51, Jan Kara wrote: > Hum, Al, did this patch get lost? > > Honza > > On Thu 24-09-20 16:58:56, Jan Kara wrote: >> On Thu 24-09-20 13:59:58, Hao Li wrote: >>> If DCACHE_REFERENCED is set, fast_dput() will return true, and then >>> retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result, >>> the dentry won't be killed and the corresponding inode can't be evicted. >>> In the following example, the DAX policy can't take effects unless we >>> do a drop_caches manually. >>> >>> # DCACHE_LRU_LIST will be set >>> echo abcdefg > test.txt >>> >>> # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything >>> xfs_io -c 'chattr +x' test.txt >>> >>> # Drop caches to make DAX changing take effects >>> echo 2 > /proc/sys/vm/drop_caches >>> >>> What this patch does is preventing fast_dput() from returning true if >>> DCACHE_DONTCACHE is set. Then retain_dentry() will detect the >>> DCACHE_DONTCACHE and will return false. As a result, the dentry will be >>> killed and the inode will be evicted. In this way, if we change per-file >>> DAX policy, it will take effects automatically after this file is closed >>> by all processes. >>> >>> I also add some comments to make the code more clear. >>> >>> Signed-off-by: Hao Li >> The patch looks good to me. You can add: >> >> Reviewed-by: Jan Kara >> >> Honza >> >>> --- >>> v1 is split into two standalone patch as discussed in [1], and the first >>> patch has been reviewed in [2]. This is the second patch. >>> >>> [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ >>> [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/ >>> >>> fs/dcache.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/dcache.c b/fs/dcache.c >>> index ea0485861d93..97e81a844a96 100644 >>> --- a/fs/dcache.c >>> +++ b/fs/dcache.c >>> @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) >>> * a reference to the dentry and change that, but >>> * our work is done - we can leave the dentry >>> * around with a zero refcount. >>> + * >>> + * Nevertheless, there are two cases that we should kill >>> + * the dentry anyway. >>> + * 1. free disconnected dentries as soon as their refcount >>> + * reached zero. >>> + * 2. free dentries if they should not be cached. >>> */ >>> smp_rmb(); >>> d_flags = READ_ONCE(dentry->d_flags); >>> - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; >>> + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | >>> + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; >>> >>> /* Nothing to do? Dropping the reference was all we needed? */ >>> if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) >>> -- >>> 2.28.0 >>> >>> >>> >> -- >> Jan Kara >> SUSE Labs, CR