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

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

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...

$ 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?

--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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