Re: [PATCH] xfs: use hardlimit as sub-fs size if both hard/soft limits are set

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Mar 26, 2018 at 12:22:59PM -0700, Darrick J. Wong wrote:
> On Sun, Mar 25, 2018 at 01:16:36PM +0800, Chengguang Xu wrote:
> > In current implementation, we size the fs(sub-fs via project quota) at
> > the soft limit and simply call it 100% used if the limit is exceeded.
> > It is reasonable when only a soft limit is set, but we should use the
> > hard limit if both hard/soft limits are set, so that quota-df reflects
> > the usage information more accurately.
> 
> This is the followup patch to "xfs: adjust size/used/avail information
> for quota-df", correct?
> 
> I also wonder, statvfs is a weird interface since there's no way to send
> back usage information, just blocks/free/avail.  Isn't it more
> appropriate to use xfs_quota to find out the usage, hard limit, and soft
> limit of a directory?
> 
> > Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
> > ---
> >  fs/xfs/xfs_qm_bhv.c | 12 ++++++------
> >  1 file changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_qm_bhv.c b/fs/xfs/xfs_qm_bhv.c
> > index 2be6d27..43b0fe8 100644
> > --- a/fs/xfs/xfs_qm_bhv.c
> > +++ b/fs/xfs/xfs_qm_bhv.c
> > @@ -35,9 +35,9 @@
> >  {
> >  	uint64_t		limit;
> >  
> > -	limit = dqp->q_core.d_blk_softlimit ?
> > -		be64_to_cpu(dqp->q_core.d_blk_softlimit) :
> > -		be64_to_cpu(dqp->q_core.d_blk_hardlimit);
> > +	limit = dqp->q_core.d_blk_hardlimit ?
> > +		be64_to_cpu(dqp->q_core.d_blk_hardlimit) :
> > +		be64_to_cpu(dqp->q_core.d_blk_softlimit);
> 
> Ok, so now we report hard limit for f_blocks over the soft limit.  So if
> this is the state of the filesystem:
> 
> # xfs_quota -xc 'report -ahp'
> Project quota on /opt (/dev/sdf)
>                         Blocks              
> Project ID   Used   Soft   Hard Warn/Grace   
> ---------- --------------------------------- 
> #0              0      0      0  00 [------]
> vms            3M     2M     3M  00 [7 days]
> 
> Then the df output goes from:
> 
> # df /opt/b
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sdf        2.0M  2.0M     0 100% /opt
> 
> to this:
> 
> # df /opt/b
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sdf        3.0M  3.0M     0 100% /opt
> 
> That makes to me, but as it /does/ change the behavior of an existing
> user-visible interface, I would like to know more about the current
> behavior.  Dave/Christoph, do you recall why df reports the project
> quota soft limit?
> 
> ----
> 
> Just for fun let's try the same on ext4...
> 
> $ dd if=/dev/zero >> /opt/b/a
> ^C4129977+0 records in
> 4129977+0 records out
> 2114548224 bytes (2.1 GB, 2.0 GiB) copied, 23.9179 s, 88.4 MB/s
> 
> $ sudo xfs_quota -fxc 'report -ahp' /opt
> Project quota on /opt (/dev/sdf)
>                         Blocks              
> Project ID   Used   Soft   Hard Warn/Grace   
> ---------- --------------------------------- 
> #0            20K      0      0  00 [------]
> vms          2.0G     2M     3M  00 [-none-]
> 
> <facepalm>
> 
> Only 1000x over soft quota...

Heh.  One has to format with project quotas /and/ mount with prjquota.

> $ df /opt/b
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sdf         13G  2.8G  8.9G  24% /opt
> 
> I guess we're going to need a couple more tests, then?  One to check
> that we enforce project quotas, and another to check what we're
> reporting via df?

I think generic/386 tests the df results with project quota...?

> --D
> 
> >  	if (limit && statp->f_blocks > limit) {
> >  		statp->f_blocks = limit;
> >  		statp->f_bfree = statp->f_bavail =
> > @@ -45,9 +45,9 @@
> >  			 (statp->f_blocks - dqp->q_res_bcount) : 0;
> >  	}
> >  
> > -	limit = dqp->q_core.d_ino_softlimit ?
> > -		be64_to_cpu(dqp->q_core.d_ino_softlimit) :
> > -		be64_to_cpu(dqp->q_core.d_ino_hardlimit);
> > +	limit = dqp->q_core.d_ino_hardlimit ?
> > +		be64_to_cpu(dqp->q_core.d_ino_hardlimit) :
> > +		be64_to_cpu(dqp->q_core.d_ino_softlimit);
> >  	if (limit && statp->f_files > limit) {
> >  		statp->f_files = limit;
> >  		statp->f_ffree =
> > -- 
> > 1.8.3.1
> > 
> > --
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