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

Dave Chinner
2014-02-24T23:56:20Z

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?

> - 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().

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;

> +
> + /* 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....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com