From 46eeb521b95247170d2db773bb4cc8fb3de1d85c Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong@oracle.com>
Date: Mon, 3 Oct 2016 09:11:16 -0700
Subject: xfs: introduce refcount btree definitions
Add new per-AG refcount btree definitions to the per-AG structures.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/libxfs/xfs_rmap_btree.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
(limited to 'fs/xfs/libxfs/xfs_rmap_btree.c')
diff --git a/fs/xfs/libxfs/xfs_rmap_btree.c b/fs/xfs/libxfs/xfs_rmap_btree.c
index 17b8eeb34ac8..9c0585e7db1f 100644
--- a/fs/xfs/libxfs/xfs_rmap_btree.c
+++ b/fs/xfs/libxfs/xfs_rmap_btree.c
@@ -512,6 +512,24 @@ void
xfs_rmapbt_compute_maxlevels(
struct xfs_mount *mp)
{
- mp->m_rmap_maxlevels = xfs_btree_compute_maxlevels(mp,
- mp->m_rmap_mnr, mp->m_sb.sb_agblocks);
+ /*
+ * On a non-reflink filesystem, the maximum number of rmap
+ * records is the number of blocks in the AG, hence the max
+ * rmapbt height is log_$maxrecs($agblocks). However, with
+ * reflink each AG block can have up to 2^32 (per the refcount
+ * record format) owners, which means that theoretically we
+ * could face up to 2^64 rmap records.
+ *
+ * That effectively means that the max rmapbt height must be
+ * XFS_BTREE_MAXLEVELS. "Fortunately" we'll run out of AG
+ * blocks to feed the rmapbt long before the rmapbt reaches
+ * maximum height. The reflink code uses ag_resv_critical to
+ * disallow reflinking when less than 10% of the per-AG metadata
+ * block reservation since the fallback is a regular file copy.
+ */
+ if (xfs_sb_version_hasreflink(&mp->m_sb))
+ mp->m_rmap_maxlevels = XFS_BTREE_MAXLEVELS;
+ else
+ mp->m_rmap_maxlevels = xfs_btree_compute_maxlevels(mp,
+ mp->m_rmap_mnr, mp->m_sb.sb_agblocks);
}
--
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