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Date:   Wed, 06 Nov 2019 18:40:36 +0800
From:   Chengguang Xu <cgxu519@mykernel.net>
Reply-To: cgxu519@mykernel.net
To:     "Jan Kara" <jack@suse.cz>
Cc:     "adilger.kernel" <adilger.kernel@dilger.ca>,
        "tytso" <tytso@mit.edu>, "Jan Kara" <jack@suse.com>,
        "linux-ext4" <linux-ext4@vger.kernel.org>
Message-ID: <16e404d465e.ddfd6f53546.5756417115406096069@mykernel.net>
In-Reply-To: <20191106094924.GA16085@quack2.suse.cz>
References: <20191015102327.5333-1-cgxu519@mykernel.net>
 <20191015112523.GB29554@quack2.suse.cz>
 <16e3f00ed3d.da5d5acd1285.2289879597060795256@mykernel.net> <20191106094924.GA16085@quack2.suse.cz>
Subject: Re: [PATCH v2] ext4: choose hardlimit when softlimit is larger than
 hardlimit in ext4_statfs_project()
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 ---- =E5=9C=A8 =E6=98=9F=E6=9C=9F=E4=B8=89, 2019-11-06 17:49:24 Jan Kara <=
jack@suse.cz> =E6=92=B0=E5=86=99 ----
 > On Wed 06-11-19 12:37:35, Chengguang Xu wrote:
 > >  ---- =E5=9C=A8 =E6=98=9F=E6=9C=9F=E4=BA=8C, 2019-10-15 19:25:23 Jan K=
ara <jack@suse.cz> =E6=92=B0=E5=86=99 ----
 > >  > On Tue 15-10-19 18:23:27, Chengguang Xu wrote:
 > >  > > Setting softlimit larger than hardlimit seems meaningless
 > >  > > for disk quota but currently it is allowed. In this case,
 > >  > > there may be a bit of comfusion for users when they run
 > >  > > df comamnd to directory which has project quota.
 > >  > >=20
 > >  > > For example, we set 20M softlimit and 10M hardlimit of
 > >  > > block usage limit for project quota of test_dir(project id 123).
 > >  > >=20
 > >  > > [root@hades mnt_ext4]# repquota -P -a
 > >  > > *** Report for project quotas on device /dev/loop0
 > >  > > Block grace time: 7days; Inode grace time: 7days
 > >  > >                         Block limits                File limits
 > >  > > Project         used    soft    hard  grace    used  soft  hard  =
grace
 > >  > > -----------------------------------------------------------------=
-----
 > >  > >  0        --      13       0       0              2     0     0
 > >  > >  123      --   10237   20480   10240              5   200   100
 > >  > >=20
 > >  > > The result of df command as below:
 > >  > >=20
 > >  > > [root@hades mnt_ext4]# df -h test_dir
 > >  > > Filesystem      Size  Used Avail Use% Mounted on
 > >  > > /dev/loop0       20M   10M   10M  50% /home/cgxu/test/mnt_ext4
 > >  > >=20
 > >  > > Even though it looks like there is another 10M free space to use,
 > >  > > if we write new data to diretory test_dir(inherit project id),
 > >  > > the write will fail with errno(-EDQUOT).
 > >  > >=20
 > >  > > After this patch, the df result looks like below.
 > >  > >=20
 > >  > > [root@hades mnt_ext4]# df -h test_dir
 > >  > > Filesystem      Size  Used Avail Use% Mounted on
 > >  > > /dev/loop0       10M   10M  3.0K 100% /home/cgxu/test/mnt_ext4
 > >  > >=20
 > >  > > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
 > >  > > ---
 > >  > > - Fix a bug in the limit setting logic.
 > >  >=20
 > >  > Thanks for the patch! It looks good to me. You can add:
 > >  >=20
 > >  > Reviewed-by: Jan Kara <jack@suse.cz>
 > >  >=20
 > >=20
 > > Hi Jan,
 > >=20
 > > I have a proposal for another direction.
 > > Could we add a check for soft limit  in quota layer when setting the v=
alue?
 > > So that we could not bother with  specific file systems on statfs().=
=20
 >=20
 > What do you mean exactly? To not allow softlimit to be larger than
 > hardlimit? That would make some sense but I don't think the risk of
 > breaking some user that accidentally depends on current behavior is wort=
h
 > the few checks we can save...
 >=20
=20
Actually, I thought exactly same as you when I wrote my patch for statfs() =
of ext4.
However, even though softlimit > hardlimit, we cannot allow user to use blo=
cks or inode
more than hardlimit. IOW, the limit is always there and  fixed in this situ=
ation.
So  how about set softlimit to hardlimit when softlimit > hardlimit and ret=
urn with success?


Thanks,
Chengguang