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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 CF0C5C2D0E2 for ; Thu, 24 Sep 2020 15:28:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 96F162311A for ; Thu, 24 Sep 2020 15:28:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728445AbgIXP2D (ORCPT ); Thu, 24 Sep 2020 11:28:03 -0400 Received: from mga07.intel.com ([134.134.136.100]:58165 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728285AbgIXP2B (ORCPT ); Thu, 24 Sep 2020 11:28:01 -0400 IronPort-SDR: LgHY0KrwQPGYD8SVZHo9lC2CB9hS6VurKlP5T24v6rn3lPQtiPzUQ+fIP3LGZEhGydGACpNRA8 DUicohK0+Cow== X-IronPort-AV: E=McAfee;i="6000,8403,9753"; a="225381798" X-IronPort-AV: E=Sophos;i="5.77,298,1596524400"; d="scan'208";a="225381798" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Sep 2020 08:28:00 -0700 IronPort-SDR: LA1eFb5xMaqYkH1ryN0Tb0/RIqDte/AgdxwEvMOTpof540OpjqnWCwyWoZf1UHzvpvcAWIRBBU sPiUZx0xqZ9Q== X-IronPort-AV: E=Sophos;i="5.77,298,1596524400"; d="scan'208";a="486940874" Received: from iweiny-desk2.sc.intel.com (HELO localhost) ([10.3.52.147]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Sep 2020 08:28:00 -0700 Date: Thu, 24 Sep 2020 08:27:59 -0700 From: Ira Weiny To: Hao Li Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, david@fromorbit.com, linux-xfs@vger.kernel.org, viro@zeniv.linux.org.uk, y-goto@fujitsu.com Subject: Re: [PATCH v2] fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set Message-ID: <20200924152759.GJ2540965@iweiny-DESK2.sc.intel.com> References: <20200924055958.825515-1-lihao2018.fnst@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200924055958.825515-1-lihao2018.fnst@cn.fujitsu.com> User-Agent: Mutt/1.11.1 (2018-12-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 24, 2020 at 01:59:58PM +0800, 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 Reviewed-by: Ira Weiny > --- > 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 > > >