[PATCH v9 05/15] xfs: ignore HW which cannot atomic write a single block

John Garry
2025-04-25T16:45:54Z

From: "Darrick J. Wong" <djwong@kernel.org>

Currently only HW which can write at least 1x block is supported.

For supporting atomic writes > 1x block, a CoW-based method will also be
used and this will not be resticted to using HW which can write >= 1x
block.

However for deciding if HW-based atomic writes can be used, we need to
start adding checks for write length < HW min, which complicates the
code. Indeed, a statx field similar to unit_max_opt should also be
added for this minimum, which is undesirable.

HW which can only write > 1x blocks would be uncommon and quite weird,
so let's just not support it.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/xfs/xfs_buf.c | 41 ++++++++++++++++++++++++++++++++++-------
fs/xfs/xfs_buf.h | 3 ++-
fs/xfs/xfs_inode.h | 14 ++------------
fs/xfs/xfs_mount.c | 7 +++++++
4 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 1a2b3f06fa71..f165446a082c 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1772,6 +1772,40 @@ xfs_init_buftarg(
return -ENOMEM;
}

+/*
+ * Configure this buffer target for hardware-assisted atomic writes if the
+ * underlying block device supports is congruent with the filesystem geometry.
+ */
+void
+xfs_buftarg_config_atomic_writes(
+ struct xfs_buftarg *btp)
+{
+ struct xfs_mount *mp = btp->bt_mount;
+ unsigned int min_bytes, max_bytes;
+
+ ASSERT(btp->bt_bdev != NULL);
+
+ if (!bdev_can_atomic_write(btp->bt_bdev))
+ return;
+
+ min_bytes = bdev_atomic_write_unit_min_bytes(btp->bt_bdev);
+ max_bytes = bdev_atomic_write_unit_max_bytes(btp->bt_bdev);
+
+ /*
+ * Ignore atomic write geometry that is nonsense or doesn't even cover
+ * a single fsblock.
+ */
+ if (min_bytes > max_bytes ||
+ min_bytes > mp->m_sb.sb_blocksize ||
+ max_bytes < mp->m_sb.sb_blocksize) {
+ min_bytes = 0;
+ max_bytes = 0;
+ }
+
+ btp->bt_bdev_awu_min = min_bytes;
+ btp->bt_bdev_awu_max = max_bytes;
+}
+
struct xfs_buftarg *
xfs_alloc_buftarg(
struct xfs_mount *mp,
@@ -1792,13 +1826,6 @@ xfs_alloc_buftarg(
btp->bt_daxdev = fs_dax_get_by_bdev(btp->bt_bdev, &btp->bt_dax_part_off,
mp, ops);

- if (bdev_can_atomic_write(btp->bt_bdev)) {
- btp->bt_bdev_awu_min = bdev_atomic_write_unit_min_bytes(
- btp->bt_bdev);
- btp->bt_bdev_awu_max = bdev_atomic_write_unit_max_bytes(
- btp->bt_bdev);
- }
-
/*
* When allocating the buftargs we have not yet read the super block and
* thus don't know the file system sector size yet.
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index d0b065a9a9f0..6f691779887f 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -112,7 +112,7 @@ struct xfs_buftarg {
struct percpu_counter bt_readahead_count;
struct ratelimit_state bt_ioerror_rl;

- /* Atomic write unit values */
+ /* Atomic write unit values, bytes */
unsigned int bt_bdev_awu_min;
unsigned int bt_bdev_awu_max;

@@ -375,6 +375,7 @@ extern void xfs_free_buftarg(struct xfs_buftarg *);
extern void xfs_buftarg_wait(struct xfs_buftarg *);
extern void xfs_buftarg_drain(struct xfs_buftarg *);
extern int xfs_setsize_buftarg(struct xfs_buftarg *, unsigned int);
+void xfs_buftarg_config_atomic_writes(struct xfs_buftarg *btp);

#define xfs_getsize_buftarg(buftarg) block_size((buftarg)->bt_bdev)
#define xfs_readonly_buftarg(buftarg) bdev_read_only((buftarg)->bt_bdev)
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index bdbbff0d8d99..d7e2b902ef5c 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -356,19 +356,9 @@ static inline bool xfs_inode_has_bigrtalloc(const struct xfs_inode *ip)
(XFS_IS_REALTIME_INODE(ip) ? \
(ip)->i_mount->m_rtdev_targp : (ip)->i_mount->m_ddev_targp)

-static inline bool
-xfs_inode_can_hw_atomic_write(
- struct xfs_inode *ip)
+static inline bool xfs_inode_can_hw_atomic_write(const struct xfs_inode *ip)
{
- struct xfs_mount *mp = ip->i_mount;
- struct xfs_buftarg *target = xfs_inode_buftarg(ip);
-
- if (mp->m_sb.sb_blocksize < target->bt_bdev_awu_min)
- return false;
- if (mp->m_sb.sb_blocksize > target->bt_bdev_awu_max)
- return false;
-
- return true;
+ return xfs_inode_buftarg(ip)->bt_bdev_awu_max > 0;
}

/*
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 00b53f479ece..1082b322e6d6 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1082,6 +1082,13 @@ xfs_mountfs(
xfs_zone_gc_start(mp);
}

+ /* Configure hardware atomic write geometry */
+ xfs_buftarg_config_atomic_writes(mp->m_ddev_targp);
+ if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp)
+ xfs_buftarg_config_atomic_writes(mp->m_logdev_targp);
+ if (mp->m_rtdev_targp && mp->m_rtdev_targp != mp->m_ddev_targp)
+ xfs_buftarg_config_atomic_writes(mp->m_rtdev_targp);
+
return 0;

out_agresv:
--
2.31.1