xfs: use generic percpu counters for free inode counter

XFS has hand-rolled per-cpu counters for the superblock since before
there was any generic implementation. The free inode counter is not
used for any limit enforcement - the per-AG free inode counters are
used during allocation to determine if there are inode available for
allocation.

Hence we don't need any of the complexity of the hand-rolled
counters and we can simply replace them with generic per-cpu
counters similar to the inode counter.

This version introduces a xfs_mod_ifree() helper function from
Christoph Hellwig.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 0aa4428bfa31..049147776ee1 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1086,6 +1086,7 @@ xfs_fs_statfs(
         struct xfs_inode        *ip = XFS_I(dentry->d_inode);
         __uint64_t              fakeinos, id;
         __uint64_t              icount;
+        __uint64_t              ifree;
         xfs_extlen_t            lsize;
         __int64_t               ffree;
 
@@ -1098,6 +1099,7 @@ xfs_fs_statfs(
 
         xfs_icsb_sync_counters(mp, XFS_ICSB_LAZY_COUNT);
         icount = percpu_counter_sum(&mp->m_icount);
+        ifree = percpu_counter_sum(&mp->m_ifree);
 
         spin_lock(&mp->m_sb_lock);
         statp->f_bsize = sbp->sb_blocksize;
@@ -1118,7 +1120,7 @@ xfs_fs_statfs(
                                         sbp->sb_icount);
 
         /* make sure statp->f_ffree does not underflow */
-        ffree = statp->f_files - (icount - sbp->sb_ifree);
+        ffree = statp->f_files - (icount - ifree);
         statp->f_ffree = max_t(__int64_t, ffree, 0);
 
         spin_unlock(&mp->m_sb_lock);