xfs: rmap btree requires more reserved free space

Originally-From: Dave Chinner <dchinner@redhat.com>

The rmap btree is allocated from the AGFL, which means we have to
ensure ENOSPC is reported to userspace before we run out of free
space in each AG. The last allocation in an AG can cause a full
height rmap btree split, and that means we have to reserve at least
this many blocks *in each AG* to be placed on the AGFL at ENOSPC.
Update the various space calculation functions to handle this.

Also, because the macros are now executing conditional code and are
called quite frequently, convert them to functions that initialise
variables in the struct xfs_mount, use the new variables everywhere
and document the calculations better.

[darrick.wong@oracle.com: don't reserve blocks if !rmap]
[dchinner@redhat.com: update m_ag_max_usable after growfs]

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 0ed0f29ddaf5..b36676cde103 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -123,6 +123,8 @@ typedef struct xfs_mount {
 	uint			m_in_maxlevels;	/* max inobt btree levels. */
 	uint			m_rmap_maxlevels; /* max rmap btree levels */
 	xfs_extlen_t		m_ag_prealloc_blocks; /* reserved ag blocks */
+	uint			m_alloc_set_aside; /* space we can't use */
+	uint			m_ag_max_usable; /* max space per AG */
 	struct radix_tree_root	m_perag_tree;	/* per-ag accounting info */
 	spinlock_t		m_perag_lock;	/* lock for m_perag_tree */
 	struct mutex		m_growlock;	/* growfs mutex */