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,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 91D9FC388F9 for ; Wed, 21 Oct 2020 13:51:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 43962221FC for ; Wed, 21 Oct 2020 13:51:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2441983AbgJUNvg (ORCPT ); Wed, 21 Oct 2020 09:51:36 -0400 Received: from mx2.suse.de ([195.135.220.15]:48496 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2439766AbgJUNvg (ORCPT ); Wed, 21 Oct 2020 09:51:36 -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 71E9FACE6; Wed, 21 Oct 2020 13:51:33 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 1AADC1E0E89; Wed, 21 Oct 2020 15:51:33 +0200 (CEST) Date: Wed, 21 Oct 2020 15:51:33 +0200 From: Jan Kara To: Al Viro Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, david@fromorbit.com, ira.weiny@intel.com, linux-xfs@vger.kernel.org, viro@zeniv.linux.org.uk, y-goto@fujitsu.com, Hao Li Subject: Re: [PATCH v2] fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set Message-ID: <20201021135133.GA25702@quack2.suse.cz> References: <20200924055958.825515-1-lihao2018.fnst@cn.fujitsu.com> <20200924145856.GB3361@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200924145856.GB3361@quack2.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org 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 -- Jan Kara SUSE Labs, CR