xfs: don't reserve per-AG space for an internal log

It turns out that the log can consume nearly all the space in an AG, and
when this happens this it's possible that there will be less free space
in the AG than the reservation would try to hide.  On a debug kernel
this can trigger an ASSERT in xfs/250:

XFS: Assertion failed: xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved + xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved <= pag->pagf_freeblks + pag->pagf_flcount, file: fs/xfs/libxfs/xfs_ag_resv.c, line: 319

The log is permanently allocated, so we know we're never going to have
to expand the btrees to hold any records associated with the log space.
We therefore can treat the space as if it doesn't exist.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>

fs/xfs/libxfs/xfs_ialloc_btree.c

@@ -549,6 +549,15 @@ xfs_inobt_max_size(
 	if (mp->m_inobt_mxr[0] == 0)
 		return 0;
 
+	/*
+	 * The log is permanently allocated, so the space it occupies will
+	 * never be available for the kinds of things that would require btree
+	 * expansion.  We therefore can pretend the space isn't there.
+	 */
+	if (mp->m_sb.sb_logstart &&
+	    XFS_FSB_TO_AGNO(mp, mp->m_sb.sb_logstart) == agno)
+		agblocks -= mp->m_sb.sb_logblocks;
+
 	return xfs_btree_calc_size(mp->m_inobt_mnr,
 				(uint64_t)agblocks * mp->m_sb.sb_inopblock /
 					XFS_INODES_PER_CHUNK);

fs/xfs/libxfs/xfs_refcount_btree.c

@@ -427,6 +427,15 @@ xfs_refcountbt_calc_reserves(
 	tree_len = be32_to_cpu(agf->agf_refcount_blocks);
 	xfs_trans_brelse(tp, agbp);
 
+	/*
+	 * The log is permanently allocated, so the space it occupies will
+	 * never be available for the kinds of things that would require btree
+	 * expansion.  We therefore can pretend the space isn't there.
+	 */
+	if (mp->m_sb.sb_logstart &&
+	    XFS_FSB_TO_AGNO(mp, mp->m_sb.sb_logstart) == agno)
+		agblocks -= mp->m_sb.sb_logblocks;
+
 	*ask += xfs_refcountbt_max_size(mp, agblocks);
 	*used += tree_len;
 

fs/xfs/libxfs/xfs_rmap_btree.c

@@ -578,6 +578,15 @@ xfs_rmapbt_calc_reserves(
 	tree_len = be32_to_cpu(agf->agf_rmap_blocks);
 	xfs_trans_brelse(tp, agbp);
 
+	/*
+	 * The log is permanently allocated, so the space it occupies will
+	 * never be available for the kinds of things that would require btree
+	 * expansion.  We therefore can pretend the space isn't there.
+	 */
+	if (mp->m_sb.sb_logstart &&
+	    XFS_FSB_TO_AGNO(mp, mp->m_sb.sb_logstart) == agno)
+		agblocks -= mp->m_sb.sb_logblocks;
+
 	/* Reserve 1% of the AG or enough for 1 block per record. */
 	*ask += max(agblocks / 100, xfs_rmapbt_max_size(mp, agblocks));
 	*used += tree_len;