Re: Weird behaviour with project quotas

[Emmanuel Florac <eflorac@intellique.com>]

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Le Thu, 12 Dec 2024 12:25:47 -0800
"Darrick J. Wong" <djwong@kernel.org> écrivait:


> Does this recreate the symptoms?
> 
<snip>
> # df /mnt /mnt/dir
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sda         20G  420M   20G   3% /mnt
> /dev/sda        2.0G     0  2.0G   0% /mnt
> # fallocate -l 19g /mnt/a
> # df /mnt /mnt/dir
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sda         20G   20G  345M  99% /mnt
> /dev/sda        2.0G     0  2.0G   0% /mnt
> 
> Clearly, df should be reporting 345M available for both cases, since
> we haven't actually used any of project 55's blocks.
> 
> # xfs_io -f -c 'pwrite -S 0x59 0 1m' -c fsync -c 'stat -vvvv'
> /mnt/dir/fork wrote 1048576/1048576 bytes at offset 0
> 1 MiB, 256 ops; 0.0008 sec (1.121 GiB/sec and 293915.0402 ops/sec)
> fd.path = "/mnt/dir/fork"
> fd.flags = non-sync,non-direct,read-write
> stat.ino = 134
> stat.type = regular file
> stat.size = 1048576
> stat.blocks = 2048
> stat.atime = Thu Dec 12 12:11:06 2024
> stat.mtime = Thu Dec 12 12:11:06 2024
> stat.ctime = Thu Dec 12 12:11:06 2024
> fsxattr.xflags = 0x0 []
> fsxattr.projid = 55
> fsxattr.extsize = 0
> fsxattr.cowextsize = 0
> fsxattr.nextents = 1
> fsxattr.naextents = 0
> dioattr.mem = 0x200
> dioattr.miniosz = 512
> dioattr.maxiosz = 2147483136
> # df /mnt /mnt/dir
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sda         20G   20G  344M  99% /mnt
> /dev/sda        2.0G  1.0M  2.0G   1% /mnt
> 
> I think this behavior comes from xfs_fill_statvfs_from_dquot, which
> does this:
> 
> 	limit = blkres->softlimit ?
> 		blkres->softlimit :
> 		blkres->hardlimit;
> 	if (limit && statp->f_blocks > limit) {
> 		statp->f_blocks = limit;
> 		statp->f_bfree = statp->f_bavail =
> 			(statp->f_blocks > blkres->reserved) ?
> 			 (statp->f_blocks - blkres->reserved) : 0;
> 	}
> 
> I think the f_bfree/f_bavail assignment is wrong because it doesn't
> handle the case where f_bfree was less than (limit - reserved).
> 
> 	if (limit) {
> 		uint64_t	remaining = 0;
> 
> 		if (statp->f_blocks > limit)
> 			statp->f_blocks = limit;
> 		if (limit > blkres->reserved)
> 			remaining = limit - blkres->reserved;
> 		statp->f_bfree = min(statp->f_bfree, remaining);
> 		statp->f_bavail = min(statp->f_bavail, remaining);
> 	}
> 
> This fixes the df output a bit:
> # df /mnt /mnt/dir
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sda         20G   20G  344M  99% /mnt
> /dev/sda        2.0G  1.7G  344M  84% /mnt
> 
> Though the "used" column is nonsense now.  But I guess that's why
> statfs only defines total blocks and free/available blocks.

Yep, that looks exactly like the problem we've met. Does the fact that
not all folders have project quota change something in that case ?

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   Emmanuel Florac     |   Direction technique
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