Re: [PATCH V2] xfs: be honest about used inodes in statfs

Eric Sandeen
2014-02-25T00:02:49Z

On 2/24/14, 5:56 PM, Dave Chinner wrote:
> On Mon, Feb 24, 2014 at 05:10:31PM -0600, Eric Sandeen wrote:
>> Because we have lazy counters, it's possible that we over-allocate
>> inodes past the maxicount (imaxpct) limit.
>>
>> A previous commit,
>>
>> 2fe3366 xfs: ensure f_ffree returned by statfs() is non-negative
>>
>> stopped statfs from underflowing f_ffree in this case, but that
>> only happened when we mis-reported f_files, capped at maxicount.
>>
>> Change statfs to report the actual number of inodes allocated,
>> even if it is greater than maxicount. It's reality.
>> Deal with it.
>>
>> (New clearer code flow thanks to Brian!)
>>
>> Logic-made-readable-by: Brian Foster <bfoster@redhat.com>
>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>> ---
>>
>> V2: Use Brian's suggested logic for working out the numbers
>>
>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
>> index f317488..0dbcc17 100644
>> --- a/fs/xfs/xfs_super.c
>> +++ b/fs/xfs/xfs_super.c
>> @@ -1083,7 +1083,6 @@ xfs_fs_statfs(
>> struct xfs_inode *ip = XFS_I(dentry->d_inode);
>> __uint64_t fakeinos, id;
>> xfs_extlen_t lsize;
>> - __int64_t ffree;
>>
>> statp->f_type = XFS_SB_MAGIC;
>> statp->f_namelen = MAXNAMELEN - 1;
>> @@ -1100,17 +1099,19 @@ xfs_fs_statfs(
>> statp->f_blocks = sbp->sb_dblocks - lsize;
>> statp->f_bfree = statp->f_bavail =
>> sbp->sb_fdblocks - XFS_ALLOC_SET_ASIDE(mp);
>> + /*
>> + * Potential number of new inodes in free blocks, limited by maxicount.
>> + */
>> fakeinos = statp->f_bfree << sbp->sb_inopblog;
>
> Can we rename "fakeinos" to something like "free_inodes" so that
> the code reads a little bit better while we are touching this
> code?

yeah, I thought about that too.

>> - statp->f_files =
>> - MIN(sbp->sb_icount + fakeinos, (__uint64_t)XFS_MAXINUMBER);
>> if (mp->m_maxicount)
>> - statp->f_files = min_t(typeof(statp->f_files),
>> - statp->f_files,
>> - mp->m_maxicount);
>> + fakeinos = mp->m_maxicount > sbp->sb_icount ?
>> + MIN(mp->m_maxicount - sbp->sb_icount, fakeinos) : 0;
>
> Get rid of MIN - it should be min() or min_t().

they are the same types, but yeah, that's better.

> Also the mix of if() and ternary operations makes this difficult to
> follow the logic. Better, IMO, is this:
>
> free_inodes = statp->f_bfree << sbp->sb_inopblog;
> if (mp->m_maxicount > sbp->sb_icount)
> free_inodes = min(mp->m_maxicount - sbp->sb_icount,
> free_inodes);
> else if (mp->m_maxicount)
> free_inodes = 0;

ok good point.

>
>> +
>> + /* Total possible files is current inodes + potential new inodes */
>> + statp->f_files = MIN(sbp->sb_icount + fakeinos,
>> + (__uint64_t) XFS_MAXINUMBER);
>
> statp->f_files = min_t(u64, sbp->sb_icount + free_inodes,
> XFS_MAXINUMBER);
>
> And for bonus points: while we are looking at maxicount, the setting
> on maxicount in the growfs code should call xfs_set_maxicount()
> rather than open coding it, and xfs_set_maxicount() needs to be
> reworked to prevent overflow when sbp->sb_dblocks * sbp->sb_imax_pct
> is greater than 64 bits....

Ok. Well, that's a different patch I think.

I'll also have to invent another tag for you, Dave.

Nitpicked-by: perhaps. ;) (I kid! I kid!)

-Eric

> Cheers,
>
> Dave.