[PATCH 084/145] xfs: refcount btree requires more reserved space

["Darrick J. Wong" <darrick.wong@xxxxxxxxxx>]

The reference count btree is allocated from the free space, which
means that we have to ensure that an AG can't run out of free space
while performing a refcount operation.  In the pathological case each
AG block has its own refcntbt record, so we have to keep that much
space available.

v2: Calculate the maximum possible size of the rmap and refcount
btrees based on minimally-full btree blocks.  This increases the
per-AG block reservations to handle the worst case btree size.

Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
 libxfs/xfs_alloc.c          |    3 +++
 libxfs/xfs_refcount_btree.c |   23 +++++++++++++++++++++++
 libxfs/xfs_refcount_btree.h |    4 ++++
 3 files changed, 30 insertions(+)


diff --git a/libxfs/xfs_alloc.c b/libxfs/xfs_alloc.c
index 6554ce7..ca3e7ce 100644
--- a/libxfs/xfs_alloc.c
+++ b/libxfs/xfs_alloc.c
@@ -34,6 +34,7 @@
 #include "xfs_trace.h"
 #include "xfs_trans.h"
 #include "xfs_ag_resv.h"
+#include "xfs_refcount_btree.h"
 
 struct workqueue_struct *xfs_alloc_wq;
 
@@ -134,6 +135,8 @@ xfs_alloc_ag_max_usable(struct xfs_mount *mp)
                /* rmap root block + full tree split on full AG */
                blocks += 1 + (2 * mp->m_ag_maxlevels) - 1;
        }
+       if (xfs_sb_version_hasreflink(&mp->m_sb))
+               blocks += xfs_refcountbt_max_size(mp);
 
        return mp->m_sb.sb_agblocks - blocks;
 }
diff --git a/libxfs/xfs_refcount_btree.c b/libxfs/xfs_refcount_btree.c
index 8c53e71..8c1cba9 100644
--- a/libxfs/xfs_refcount_btree.c
+++ b/libxfs/xfs_refcount_btree.c
@@ -372,3 +372,26 @@ xfs_refcountbt_compute_maxlevels(
        mp->m_refc_maxlevels = xfs_btree_compute_maxlevels(mp,
                        mp->m_refc_mnr, mp->m_sb.sb_agblocks);
 }
+
+/* Calculate the refcount btree size for some records. */
+xfs_extlen_t
+xfs_refcountbt_calc_size(
+       struct xfs_mount        *mp,
+       unsigned long long      len)
+{
+       return xfs_btree_calc_size(mp, mp->m_refc_mnr, len);
+}
+
+/*
+ * Calculate the maximum refcount btree size.
+ */
+xfs_extlen_t
+xfs_refcountbt_max_size(
+       struct xfs_mount        *mp)
+{
+       /* Bail out if we're uninitialized, which can happen in mkfs. */
+       if (mp->m_refc_mxr[0] == 0)
+               return 0;
+
+       return xfs_refcountbt_calc_size(mp, mp->m_sb.sb_agblocks);
+}
diff --git a/libxfs/xfs_refcount_btree.h b/libxfs/xfs_refcount_btree.h
index 9e9ad7c..780b02f 100644
--- a/libxfs/xfs_refcount_btree.h
+++ b/libxfs/xfs_refcount_btree.h
@@ -64,4 +64,8 @@ extern int xfs_refcountbt_maxrecs(struct xfs_mount *mp, int 
blocklen,
                bool leaf);
 extern void xfs_refcountbt_compute_maxlevels(struct xfs_mount *mp);
 
+extern xfs_extlen_t xfs_refcountbt_calc_size(struct xfs_mount *mp,
+               unsigned long long len);
+extern xfs_extlen_t xfs_refcountbt_max_size(struct xfs_mount *mp);
+
 #endif /* __XFS_REFCOUNT_BTREE_H__ */