[PATCH v2 5/7] xfs: include an allocfree res for inobt modifications

[Brian Foster <bfoster@redhat.com>]

Analysis of recent reports of log reservation overruns and code
inspection has uncovered that the reservations associated with inode
operations may not cover the worst case scenarios. In particular,
many cases only include one allocfree res. for a particular
operation even though said operations may also entail AGFL fixups
and inode btree block allocations in addition to the actual inode
chunk allocation. This can easily turn into two or three block
allocations (or frees) per operation.

In theory, the only way to define the worst case reservation is to
include an allocfree res for each individual allocation in a
transaction. Since that is impractical (we can perform multiple agfl
fixups per tx and not every allocation results in a full tree
operation), we need to find a reasonable compromise that addresses
the deficiency in practice without blowing out the size of the
transactions.

Since the inode btrees are not filled by the AGFL, record insertion
and removal can directly result in block allocations and frees
depending on the shape of the tree. These allocations and frees
occur in the same transaction context as the inobt update itself,
but are separate from the allocation/free that might be required for
an inode chunk. Therefore, it makes sense to assume that an [f]inobt
insert/remove can directly result in one or more block allocations
on behalf of the tree.

Refactor the inode transaction reservations to include one allocfree
res. per inode btree modification to cover allocations required by
the tree itself. This separates the reservation required to allocate
the inode chunk from the reservation required for inobt record
insertion/removal. Apply the same logic to the finobt. This results
in killing off the finobt modify condition because we no longer
assume that the broader transaction reservation will cover finobt
block allocations and finobt shape changes can occur in either of
the inobt allocation or modify situations.

Suggested-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/libxfs/xfs_trans_resv.c | 84 +++++++++++++++++++++---------------------
 1 file changed, 43 insertions(+), 41 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
index 037a1295d289..19f3a226a357 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.c
+++ b/fs/xfs/libxfs/xfs_trans_resv.c
@@ -132,44 +132,43 @@ xfs_calc_inode_res(
 }
 
 /*
- * The free inode btree is a conditional feature and the log reservation
- * requirements differ slightly from that of the traditional inode allocation
- * btree. The finobt tracks records for inode chunks with at least one free
- * inode. A record can be removed from the tree for an inode allocation
- * or free and thus the finobt reservation is unconditional across:
+ * Inode btree record insertion/removal modifies the inode btree and free space
+ * btrees (since the inobt does not use the agfl). This requires the following
+ * reservation:
  *
- * 	- inode allocation
- * 	- inode free
- * 	- inode chunk allocation
+ * the inode btree: max depth * blocksize
+ * the allocation btrees: 2 trees * (max depth - 1) * block size
  *
- * The 'modify' param indicates to include the record modification scenario. The
- * 'alloc' param indicates to include the reservation for free space btree
- * modifications on behalf of finobt modifications. This is required only for
- * transactions that do not already account for free space btree modifications.
+ * The caller must account for SB and AG header modifications, etc.
+ */
+STATIC uint
+xfs_calc_inobt_res(
+	struct xfs_mount	*mp)
+{
+	return xfs_calc_buf_res(mp->m_in_maxlevels, XFS_FSB_TO_B(mp, 1)) +
+		xfs_calc_buf_res(xfs_allocfree_log_count(mp, 1),
+				 XFS_FSB_TO_B(mp, 1));
+}
+
+/*
+ * The free inode btree is a conditional feature. The behavior differs slightly
+ * from that of the traditional inode btree in that the finobt tracks records
+ * for inode chunks with at least one free inode. A record can be removed from
+ * the tree during individual inode allocation. Therefore the finobt
+ * reservation is unconditional for both the inode chunk allocation and
+ * individual inode allocation (modify) cases.
  *
- * the free inode btree: max depth * block size
- * the allocation btrees: 2 trees * (max depth - 1) * block size
- * the free inode btree entry: block size
+ * Behavior aside, the reservation for finobt modification is equivalent to the
+ * traditional inobt: cover a full finobt shape change plus block allocation.
  */
 STATIC uint
 xfs_calc_finobt_res(
-	struct xfs_mount	*mp,
-	int			alloc,
-	int			modify)
+	struct xfs_mount	*mp)
 {
-	uint res;
-
 	if (!xfs_sb_version_hasfinobt(&mp->m_sb))
 		return 0;
 
-	res = xfs_calc_buf_res(mp->m_in_maxlevels, XFS_FSB_TO_B(mp, 1));
-	if (alloc)
-		res += xfs_calc_buf_res(xfs_allocfree_log_count(mp, 1),
-					XFS_FSB_TO_B(mp, 1));
-	if (modify)
-		res += (uint)XFS_FSB_TO_B(mp, 1);
-
-	return res;
+	return xfs_calc_inobt_res(mp);
 }
 
 /*
@@ -373,7 +372,7 @@ xfs_calc_create_resv_modify(
 		xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
 		(uint)XFS_FSB_TO_B(mp, 1) +
 		xfs_calc_buf_res(XFS_DIROP_LOG_COUNT(mp), XFS_FSB_TO_B(mp, 1)) +
-		xfs_calc_finobt_res(mp, 1, 1);
+		xfs_calc_finobt_res(mp);
 }
 
 /*
@@ -381,8 +380,8 @@ xfs_calc_create_resv_modify(
  *    the agi and agf of the ag getting the new inodes: 2 * sectorsize
  *    the superblock for the nlink flag: sector size
  *    the inode blocks allocated: mp->m_ialloc_blks * blocksize
- *    the inode btree: max depth * blocksize
  *    the allocation btrees: 2 trees * (max depth - 1) * block size
+ *    the inode btree (record insertion)
  */
 STATIC uint
 xfs_calc_create_resv_alloc(
@@ -391,9 +390,9 @@ xfs_calc_create_resv_alloc(
 	return xfs_calc_buf_res(2, mp->m_sb.sb_sectsize) +
 		mp->m_sb.sb_sectsize +
 		xfs_calc_buf_res(mp->m_ialloc_blks, XFS_FSB_TO_B(mp, 1)) +
-		xfs_calc_buf_res(mp->m_in_maxlevels, XFS_FSB_TO_B(mp, 1)) +
 		xfs_calc_buf_res(xfs_allocfree_log_count(mp, 1),
-				 XFS_FSB_TO_B(mp, 1));
+				 XFS_FSB_TO_B(mp, 1)) +
+		xfs_calc_inobt_res(mp);
 }
 
 STATIC uint
@@ -409,8 +408,8 @@ __xfs_calc_create_reservation(
  * For icreate we can allocate some inodes giving:
  *    the agi and agf of the ag getting the new inodes: 2 * sectorsize
  *    the superblock for the nlink flag: sector size
- *    the inode btree: max depth * blocksize
  *    the allocation btrees: 2 trees * (max depth - 1) * block size
+ *    the inobt (record insertion)
  *    the finobt (record insertion)
  */
 STATIC uint
@@ -419,10 +418,10 @@ xfs_calc_icreate_resv_alloc(
 {
 	return xfs_calc_buf_res(2, mp->m_sb.sb_sectsize) +
 		mp->m_sb.sb_sectsize +
-		xfs_calc_buf_res(mp->m_in_maxlevels, XFS_FSB_TO_B(mp, 1)) +
 		xfs_calc_buf_res(xfs_allocfree_log_count(mp, 1),
 				 XFS_FSB_TO_B(mp, 1)) +
-		xfs_calc_finobt_res(mp, 0, 0);
+		xfs_calc_inobt_res(mp) +
+		xfs_calc_finobt_res(mp);
 }
 
 STATIC uint
@@ -487,9 +486,14 @@ xfs_calc_symlink_reservation(
  *    the super block free inode counter, AGF and AGFL: sector size
  *    the on disk inode (agi unlinked list removal)
  *    the inode chunk is marked stale (headers only)
- *    the inode btree: max depth * blocksize
- *    the allocation btrees: 2 trees * (max depth - 1) * block size
+ *    the inode btree
  *    the finobt (record insertion, removal or modification)
+ *
+ * Note that the allocfree res. for the inode chunk itself is not included
+ * because the extent free occurs after a transaction roll. We could take the
+ * maximum of the pre/post roll operations, but the pre-roll reservation already
+ * includes at least one allocfree res. for the inobt and is thus guaranteed to
+ * be larger.
  */
 STATIC uint
 xfs_calc_ifree_reservation(
@@ -500,10 +504,8 @@ xfs_calc_ifree_reservation(
 		xfs_calc_buf_res(3, mp->m_sb.sb_sectsize) +
 		xfs_calc_iunlink_remove_reservation(mp) +
 		xfs_calc_buf_res(mp->m_ialloc_blks, 0) +
-		xfs_calc_buf_res(mp->m_in_maxlevels, XFS_FSB_TO_B(mp, 1)) +
-		xfs_calc_buf_res(xfs_allocfree_log_count(mp, 1),
-				 XFS_FSB_TO_B(mp, 1)) +
-		xfs_calc_finobt_res(mp, 0, 1);
+		xfs_calc_inobt_res(mp) +
+		xfs_calc_finobt_res(mp);
 }
 
 /*
-- 
2.13.6