[PATCH 3/7] xfs: Compute maximum height of directory BMBT separately

Chandan Babu R
2020-06-06T08:28:23Z

xfs/306 causes the following call trace when using a data fork with a
maximum extent count of 2^47,

XFS (loop0): Mounting V5 Filesystem
XFS (loop0): Log size 8906 blocks too small, minimum size is 9075 blocks
XFS (loop0): AAIEEE! Log failed size checks. Abort!
XFS: Assertion failed: 0, file: fs/xfs/xfs_log.c, line: 711
------------[ cut here ]------------
WARNING: CPU: 0 PID: 12821 at fs/xfs/xfs_message.c:112 assfail+0x25/0x28
Modules linked in:
CPU: 0 PID: 12821 Comm: mount Tainted: G W 5.6.0-rc6-next-20200320-chandan-00003-g071c2af3f4de #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
RIP: 0010:assfail+0x25/0x28
Code: ff ff 0f 0b c3 0f 1f 44 00 00 41 89 c8 48 89 d1 48 89 f2 48 c7 c6 40 b7 4b b3 e8 82 f9 ff ff 80 3d 83 d6 64 01 00 74 02 0f $
RSP: 0018:ffffb05b414cbd78 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff9d9d501d5000 RCX: 0000000000000000
RDX: 00000000ffffffc0 RSI: 000000000000000a RDI: ffffffffb346dc65
RBP: ffff9da444b49a80 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000000a R11: f000000000000000 R12: 00000000ffffffea
R13: 000000000000000e R14: 0000000000004594 R15: ffff9d9d501d5628
FS: 00007fd6c5d17c80(0000) GS:ffff9da44d800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 00000008a48c0000 CR4: 00000000000006f0
Call Trace:
xfs_log_mount+0xf8/0x300
xfs_mountfs+0x46e/0x950
xfs_fc_fill_super+0x318/0x510
? xfs_mount_free+0x30/0x30
get_tree_bdev+0x15c/0x250
vfs_get_tree+0x25/0xb0
do_mount+0x740/0x9b0
? memdup_user+0x41/0x80
__x64_sys_mount+0x8e/0xd0
do_syscall_64+0x48/0x110
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fd6c5f2ccda
Code: 48 8b 0d b9 e1 0b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f $
RSP: 002b:00007ffe00dfb9f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000560c1aaa92c0 RCX: 00007fd6c5f2ccda
RDX: 0000560c1aaae110 RSI: 0000560c1aaad040 RDI: 0000560c1aaa94d0
RBP: 00007fd6c607d204 R08: 0000000000000000 R09: 0000560c1aaadde0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000560c1aaa94d0 R15: 0000560c1aaae110
---[ end trace 6436391b468bc652 ]---
XFS (loop0): log mount failed

The corresponding filesystem was created using mkfs options
"-m rmapbt=1,reflink=1 -b size=1k -d size=20m -n size=64k".

i.e. We have a filesystem of size 20MiB, data block size of 1KiB and
directory block size of 64KiB. Filesystems of size < 1GiB can have less
than 10MiB on-disk log (Please refer to calculate_log_size() in
xfsprogs).

The largest reservation space was contributed by the rename
operation. The corresponding calculation is done inside
xfs_calc_rename_reservation(). In this case, the value returned by this
function is,

xfs_calc_inode_res(mp, 4)
+ xfs_calc_buf_res(2 * XFS_DIROP_LOG_COUNT(mp), XFS_FSB_TO_B(mp, 1))

xfs_calc_inode_res(mp, 4) returns a constant value of 3040 bytes
regardless of the maximum data fork extent count.

The largest contribution to the rename operation was by "2 *
XFS_DIROP_LOG_COUNT(mp)" and it is a function of maximum height of a
directory's BMBT tree.

XFS_DIROP_LOG_COUNT() is a sum of,

1. The maximum number of dabtree blocks that needs to be logged
i.e. XFS_DAENTER_BLOCKS() = XFS_DAENTER_1B(mp,w) *
XFS_DAENTER_DBS(mp,w). For directories, this evaluates
to (64 * (XFS_DA_NODE_MAXDEPTH + 2)) = (64 * (5 + 2)) = 448.

2. The corresponding maximum number of BMBT blocks that needs to be
logged i.e. XFS_DAENTER_BMAPS() = XFS_DAENTER_DBS(mp,w) *
XFS_DAENTER_BMAP1B(mp,w)

XFS_DAENTER_DBS(mp,w) = XFS_DA_NODE_MAXDEPTH + 2 = 7

XFS_DAENTER_BMAP1B(mp,w)
= XFS_NEXTENTADD_SPACE_RES(mp, XFS_DAENTER_1B(mp, w), w)
= XFS_NEXTENTADD_SPACE_RES(mp, 64, w)
= ((64 + XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp) - 1) /
XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp)) * XFS_EXTENTADD_SPACE_RES(mp, w)

XFS_MAX_CONTIG_EXTENTS_PER_BLOCK() =
mp->m_alloc_mxr[0] - mp->m_alloc_mnr[0] = 121 - 60 = 61

XFS_DAENTER_BMAP1B(mp,w) =
((64 + XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp) - 1) /
XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp)) * XFS_EXTENTADD_SPACE_RES(mp, w)
= ((64 + 61 - 1) / 61) * XFS_EXTENTADD_SPACE_RES(mp, w)
= 2 * XFS_EXTENTADD_SPACE_RES(mp, w)
= 2 * (XFS_BM_MAXLEVELS(mp,w) - 1)
= 2 * (8 - 1)
= 14

With 2^32 as the maximum extent count the maximum height of the bmap btree
was 7. Now with 2^47 maximum extent count, the height has increased to 8.

Therefore, XFS_DAENTER_BMAPS() = 7 * 14 = 98.

XFS_DIROP_LOG_COUNT() = 448 + 98 = 546.
2 * XFS_DIROP_LOG_COUNT() = 2 * 546 = 1092.

With 2^32 max extent count, XFS_DIROP_LOG_COUNT() evaluates to
533. Hence 2 * XFS_DIROP_LOG_COUNT() = 2 * 533 = 1066.

This small difference of 1092 - 1066 = 26 fs blocks is sufficient to
trip us over the minimum log size check.

A future commit in this series will use 2^27 as the maximum directory
extent count. This will result in a shorter directory BMBT tree. Log
reservation calculations that are applicable only to
directories (e.g. XFS_DIROP_LOG_COUNT()) can then choose this instead of
non-dir data fork BMBT height.

This commit introduces a new member in 'struct xfs_mount' to hold the
maximum BMBT height of a directory. At present, the maximum height of a
directory BMBT is the same as a the maximum height of a non-directory
BMBT. A future commit will change the parameters used as input for
computing the maximum height of a directory BMBT.

Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
---
fs/xfs/libxfs/xfs_bmap.c | 17 ++++++++++++++---
fs/xfs/libxfs/xfs_bmap.h | 3 ++-
fs/xfs/xfs_mount.c | 5 +++--
fs/xfs/xfs_mount.h | 1 +
4 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 798fca5c52af..01e2b543b139 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -50,7 +50,8 @@ kmem_zone_t *xfs_bmap_free_item_zone;
void
xfs_bmap_compute_maxlevels(
xfs_mount_t *mp, /* file system mount structure */
- int whichfork) /* data or attr fork */
+ int whichfork, /* data or attr fork */
+ int dir_bmbt) /* Dir or non-dir data fork */
{
int level; /* btree level */
uint maxblocks; /* max blocks at this level */
@@ -60,6 +61,9 @@ xfs_bmap_compute_maxlevels(
int minnoderecs; /* min records in node block */
int sz; /* root block size */

+ if (whichfork == XFS_ATTR_FORK)
+ ASSERT(dir_bmbt == 0);
+
/*
* The maximum number of extents in a file, hence the maximum number of
* leaf entries, is controlled by the size of the on-disk extent count,
@@ -75,8 +79,11 @@ xfs_bmap_compute_maxlevels(
* of a minimum size available.
*/
if (whichfork == XFS_DATA_FORK) {
- maxleafents = MAXEXTNUM;
sz = XFS_BMDR_SPACE_CALC(MINDBTPTRS);
+ if (dir_bmbt)
+ maxleafents = MAXEXTNUM;
+ else
+ maxleafents = MAXEXTNUM;
} else {
maxleafents = MAXAEXTNUM;
sz = XFS_BMDR_SPACE_CALC(MINABTPTRS);
@@ -91,7 +98,11 @@ xfs_bmap_compute_maxlevels(
else
maxblocks = (maxblocks + minnoderecs - 1) / minnoderecs;
}
- mp->m_bm_maxlevels[whichfork] = level;
+
+ if (whichfork == XFS_DATA_FORK && dir_bmbt)
+ mp->m_bm_dir_maxlevel = level;
+ else
+ mp->m_bm_maxlevels[whichfork] = level;
}

STATIC int /* error */
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index 6028a3c825ba..4250c9ab4b75 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -187,7 +187,8 @@ void xfs_bmap_local_to_extents_empty(struct xfs_trans *tp,
void __xfs_bmap_add_free(struct xfs_trans *tp, xfs_fsblock_t bno,
xfs_filblks_t len, const struct xfs_owner_info *oinfo,
bool skip_discard);
-void xfs_bmap_compute_maxlevels(struct xfs_mount *mp, int whichfork);
+void xfs_bmap_compute_maxlevels(struct xfs_mount *mp, int whichfork,
+ int dir_bmbt);
int xfs_bmap_first_unused(struct xfs_trans *tp, struct xfs_inode *ip,
xfs_extlen_t len, xfs_fileoff_t *unused, int whichfork);
int xfs_bmap_last_before(struct xfs_trans *tp, struct xfs_inode *ip,
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index bb91f04266b9..d8ebfc67bb63 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -711,8 +711,9 @@ xfs_mountfs(
goto out;

xfs_alloc_compute_maxlevels(mp);
- xfs_bmap_compute_maxlevels(mp, XFS_DATA_FORK);
- xfs_bmap_compute_maxlevels(mp, XFS_ATTR_FORK);
+ xfs_bmap_compute_maxlevels(mp, XFS_DATA_FORK, 0);
+ xfs_bmap_compute_maxlevels(mp, XFS_DATA_FORK, 1);
+ xfs_bmap_compute_maxlevels(mp, XFS_ATTR_FORK, 0);
xfs_ialloc_setup_geometry(mp);
xfs_rmapbt_compute_maxlevels(mp);
xfs_refcountbt_compute_maxlevels(mp);
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index aba5a1579279..9dbf036ddace 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -133,6 +133,7 @@ typedef struct xfs_mount {
uint m_refc_mnr[2]; /* min refc btree records */
uint m_ag_maxlevels; /* XFS_AG_MAXLEVELS */
uint m_bm_maxlevels[2]; /* XFS_BM_MAXLEVELS */
+ uint m_bm_dir_maxlevel;
uint m_rmap_maxlevels; /* max rmap btree levels */
uint m_refc_maxlevels; /* max refcount btree level */
xfs_extlen_t m_ag_prealloc_blocks; /* reserved ag blocks */
--
2.20.1