linux-ext4 - Re: [PATCH v2] ext4: choose hardlimit when softlimit is larger than hardlimit in ext4_statfs

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Date:   Wed, 06 Nov 2019 18:52:07 +0800
From:   Chengguang Xu <cgxu519@...ernel.net>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     "Jan Kara" <jack@...e.cz>,
        "adilger.kernel" <adilger.kernel@...ger.ca>,
        "tytso" <tytso@....edu>, "Jan Kara" <jack@...e.com>,
        "linux-ext4" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: choose hardlimit when softlimit is larger than
 hardlimit in ext4_statfs_project()

 ---- 在 星期三, 2019-11-06 16:34:24 Chengguang Xu <cgxu519@...ernel.net> 撰写 ----
 >  ---- 在 星期三, 2019-11-06 13:03:36 Darrick J. Wong <darrick.wong@...cle.com> 撰写 ----
 >  > On Wed, Nov 06, 2019 at 12:37:35PM +0800, Chengguang Xu wrote:
 >  > >  ---- 在 星期二, 2019-10-15 19:25:23 Jan Kara <jack@...e.cz> 撰写 ----
 >  > >  > 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.
 >  > >  > > 
 >  > >  > > For example, we set 20M softlimit and 10M hardlimit of
 >  > >  > > block usage limit for project quota of test_dir(project id 123).
 >  > >  > > 
 >  > >  > > [root@...es 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
 >  > >  > > 
 >  > >  > > The result of df command as below:
 >  > >  > > 
 >  > >  > > [root@...es mnt_ext4]# df -h test_dir
 >  > >  > > Filesystem      Size  Used Avail Use% Mounted on
 >  > >  > > /dev/loop0       20M   10M   10M  50% /home/cgxu/test/mnt_ext4
 >  > >  > > 
 >  > >  > > 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).
 >  > >  > > 
 >  > >  > > After this patch, the df result looks like below.
 >  > >  > > 
 >  > >  > > [root@...es 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
 >  > >  > > 
 >  > >  > > Signed-off-by: Chengguang Xu <cgxu519@...ernel.net>
 >  > >  > > ---
 >  > >  > > - Fix a bug in the limit setting logic.
 >  > >  > 
 >  > >  > Thanks for the patch! It looks good to me. You can add:
 >  > >  > 
 >  > >  > Reviewed-by: Jan Kara <jack@...e.cz>
 >  > >  > 
 >  > > 
 >  > > Hi Jan,
 >  > > 
 >  > > I have a proposal for another direction.
 >  > > Could we add a check for soft limit  in quota layer when setting the value?
 >  > > So that we could not bother with  specific file systems on statfs(). 
 >  > 
 >  > How do the other filesystems (e.g. xfs) behave if someone tries to set a
 >  > soft limit higher than the hard limit?
 >  > 
 > 
 > In xfs if (hard && hard < soft), the limit will not be set(or changed) but command xfs_quota does not return error.
 > 

Hi Darrick,

IMO, set nothing and return success seems  not reasonable, 
is it possible change to set softlimit to hardlimit when softlimit > hardlimit?

Thanks,
Chengguang