xfs: use generic percpu counters for inode counter
XFS has hand-rolled per-cpu counters for the superblock since before there was any generic implementation. There are some warts around the use of them for the inode counter as the hand rolled counter is designed to be accurate at zero, but has no specific accurracy at any other value. This design causes problems for the maximum inode count threshold enforcement, as there is no trigger that balances the counters as they get close tothe maximum threshold. Instead of designing new triggers for balancing, just replace the handrolled per-cpu counter with a generic counter. This enables us to update the counter through the normal superblock modification funtions, but rather than do that we add a xfs_mod_icount() helper function (from Christoph Hellwig) and keep the percpu counter outside the superblock in the struct xfs_mount. This means we still need to initialise the per-cpu counter specifically when we read the superblock, and vice versa when we log/write it, but it does mean that we don't need to change any other code. Signed-off-by: NDave Chinner <dchinner@redhat.com> Reviewed-by: NBrian Foster <bfoster@redhat.com> Signed-off-by: NDave Chinner <david@fromorbit.com>
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