Merge tag 'ext4_for_linus-6.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4

Pull ext4 updates from Ted Ts'o:
 "New ext4 features and performance improvements:

   - Fast commit performance improvements

   - Multi-fsblock atomic write support for bigalloc file systems

   - Large folio support for regular files

  This last can result in really stupendous performance for the right
  workloads. For example, see [1] where the Kernel Test Robot reported
  over 37% improvement on a large sequential I/O workload.

  There are also the usual bug fixes and cleanups. Of note are cleanups
  of the extent status tree to fix potential races that could result in
  the extent status tree getting corrupted under heavy simultaneous
  allocation and deallocation to a single file"

Link: https://lore.kernel.org/all/202505161418.ec0d753f-lkp@intel.com/ [1]

* tag 'ext4_for_linus-6.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: (52 commits)
  ext4: Add a WARN_ON_ONCE for querying LAST_IN_LEAF instead
  ext4: Simplify flags in ext4_map_query_blocks()
  ext4: Rename and document EXT4_EX_FILTER to EXT4_EX_QUERY_FILTER
  ext4: Simplify last in leaf check in ext4_map_query_blocks
  ext4: Unwritten to written conversion requires EXT4_EX_NOCACHE
  ext4: only dirty folios when data journaling regular files
  ext4: Add atomic block write documentation
  ext4: Enable support for ext4 multi-fsblock atomic write using bigalloc
  ext4: Add multi-fsblock atomic write support with bigalloc
  ext4: Add support for EXT4_GET_BLOCKS_QUERY_LEAF_BLOCKS
  ext4: Make ext4_meta_trans_blocks() non-static for later use
  ext4: Check if inode uses extents in ext4_inode_can_atomic_write()
  ext4: Document an edge case for overwrites
  jbd2: remove journal_t argument from jbd2_superblock_csum()
  jbd2: remove journal_t argument from jbd2_chksum()
  ext4: remove sb argument from ext4_superblock_csum()
  ext4: remove sbi argument from ext4_chksum()
  ext4: enable large folio for regular file
  ext4: make online defragmentation support large folios
  ext4: make the writeback path support large folios
  ...

Author: torvalds

Documentation/filesystems/ext4/atomic_writes.rst

@@ -0,0 +1,225 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. _atomic_writes:
+
+Atomic Block Writes
+-------------------------
+
+Introduction
+~~~~~~~~~~~~
+
+Atomic (untorn) block writes ensure that either the entire write is committed
+to disk or none of it is. This prevents "torn writes" during power loss or
+system crashes. The ext4 filesystem supports atomic writes (only with Direct
+I/O) on regular files with extents, provided the underlying storage device
+supports hardware atomic writes. This is supported in the following two ways:
+
+1. **Single-fsblock Atomic Writes**:
+   EXT4's supports atomic write operations with a single filesystem block since
+   v6.13. In this the atomic write unit minimum and maximum sizes are both set
+   to filesystem blocksize.
+   e.g. doing atomic write of 16KB with 16KB filesystem blocksize on 64KB
+   pagesize system is possible.
+
+2. **Multi-fsblock Atomic Writes with Bigalloc**:
+   EXT4 now also supports atomic writes spanning multiple filesystem blocks
+   using a feature known as bigalloc. The atomic write unit's minimum and
+   maximum sizes are determined by the filesystem block size and cluster size,
+   based on the underlying device’s supported atomic write unit limits.
+
+Requirements
+~~~~~~~~~~~~
+
+Basic requirements for atomic writes in ext4:
+
+ 1. The extents feature must be enabled (default for ext4)
+ 2. The underlying block device must support atomic writes
+ 3. For single-fsblock atomic writes:
+
+    1. A filesystem with appropriate block size (up to the page size)
+ 4. For multi-fsblock atomic writes:
+
+    1. The bigalloc feature must be enabled
+    2. The cluster size must be appropriately configured
+
+NOTE: EXT4 does not support software or COW based atomic write, which means
+atomic writes on ext4 are only supported if underlying storage device supports
+it.
+
+Multi-fsblock Implementation Details
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The bigalloc feature changes ext4 to allocate in units of multiple filesystem
+blocks, also known as clusters. With bigalloc each bit within block bitmap
+represents cluster (power of 2 number of blocks) rather than individual
+filesystem blocks.
+EXT4 supports multi-fsblock atomic writes with bigalloc, subject to the
+following constraints. The minimum atomic write size is the larger of the fs
+block size and the minimum hardware atomic write unit; and the maximum atomic
+write size is smaller of the bigalloc cluster size and the maximum hardware
+atomic write unit.  Bigalloc ensures that all allocations are aligned to the
+cluster size, which satisfies the LBA alignment requirements of the hardware
+device if the start of the partition/logical volume is itself aligned correctly.
+
+Here is the block allocation strategy in bigalloc for atomic writes:
+
+ * For regions with fully mapped extents, no additional work is needed
+ * For append writes, a new mapped extent is allocated
+ * For regions that are entirely holes, unwritten extent is created
+ * For large unwritten extents, the extent gets split into two unwritten
+   extents of appropriate requested size
+ * For mixed mapping regions (combinations of holes, unwritten extents, or
+   mapped extents), ext4_map_blocks() is called in a loop with
+   EXT4_GET_BLOCKS_ZERO flag to convert the region into a single contiguous
+   mapped extent by writing zeroes to it and converting any unwritten extents to
+   written, if found within the range.
+
+Note: Writing on a single contiguous underlying extent, whether mapped or
+unwritten, is not inherently problematic. However, writing to a mixed mapping
+region (i.e. one containing a combination of mapped and unwritten extents)
+must be avoided when performing atomic writes.
+
+The reason is that, atomic writes when issued via pwritev2() with the RWF_ATOMIC
+flag, requires that either all data is written or none at all. In the event of
+a system crash or unexpected power loss during the write operation, the affected
+region (when later read) must reflect either the complete old data or the
+complete new data, but never a mix of both.
+
+To enforce this guarantee, we ensure that the write target is backed by
+a single, contiguous extent before any data is written. This is critical because
+ext4 defers the conversion of unwritten extents to written extents until the I/O
+completion path (typically in ->end_io()). If a write is allowed to proceed over
+a mixed mapping region (with mapped and unwritten extents) and a failure occurs
+mid-write, the system could observe partially updated regions after reboot, i.e.
+new data over mapped areas, and stale (old) data over unwritten extents that
+were never marked written. This violates the atomicity and/or torn write
+prevention guarantee.
+
+To prevent such torn writes, ext4 proactively allocates a single contiguous
+extent for the entire requested region in ``ext4_iomap_alloc`` via
+``ext4_map_blocks_atomic()``. EXT4 also force commits the current journalling
+transaction in case if allocation is done over mixed mapping. This ensures any
+pending metadata updates (like unwritten to written extents conversion) in this
+range are in consistent state with the file data blocks, before performing the
+actual write I/O. If the commit fails, the whole I/O must be aborted to prevent
+from any possible torn writes.
+Only after this step, the actual data write operation is performed by the iomap.
+
+Handling Split Extents Across Leaf Blocks
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There can be a special edge case where we have logically and physically
+contiguous extents stored in separate leaf nodes of the on-disk extent tree.
+This occurs because on-disk extent tree merges only happens within the leaf
+blocks except for a case where we have 2-level tree which can get merged and
+collapsed entirely into the inode.
+If such a layout exists and, in the worst case, the extent status cache entries
+are reclaimed due to memory pressure, ``ext4_map_blocks()`` may never return
+a single contiguous extent for these split leaf extents.
+
+To address this edge case, a new get block flag
+``EXT4_GET_BLOCKS_QUERY_LEAF_BLOCKS flag`` is added to enhance the
+``ext4_map_query_blocks()`` lookup behavior.
+
+This new get block flag allows ``ext4_map_blocks()`` to first check if there is
+an entry in the extent status cache for the full range.
+If not present, it consults the on-disk extent tree using
+``ext4_map_query_blocks()``.
+If the located extent is at the end of a leaf node, it probes the next logical
+block (lblk) to detect a contiguous extent in the adjacent leaf.
+
+For now only one additional leaf block is queried to maintain efficiency, as
+atomic writes are typically constrained to small sizes
+(e.g. [blocksize, clustersize]).
+
+
+Handling Journal transactions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To support multi-fsblock atomic writes, we ensure enough journal credits are
+reserved during:
+
+ 1. Block allocation time in ``ext4_iomap_alloc()``. We first query if there
+    could be a mixed mapping for the underlying requested range. If yes, then we
+    reserve credits of up to ``m_len``, assuming every alternate block can be
+    an unwritten extent followed by a hole.
+
+ 2. During ``->end_io()`` call, we make sure a single transaction is started for
+    doing unwritten-to-written conversion. The loop for conversion is mainly
+    only required to handle a split extent across leaf blocks.
+
+How to
+------
+
+Creating Filesystems with Atomic Write Support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+First check the atomic write units supported by block device.
+See :ref:`atomic_write_bdev_support` for more details.
+
+For single-fsblock atomic writes with a larger block size
+(on systems with block size < page size):
+
+.. code-block:: bash
+
+    # Create an ext4 filesystem with a 16KB block size
+    # (requires page size >= 16KB)
+    mkfs.ext4 -b 16384 /dev/device
+
+For multi-fsblock atomic writes with bigalloc:
+
+.. code-block:: bash
+
+    # Create an ext4 filesystem with bigalloc and 64KB cluster size
+    mkfs.ext4 -F -O bigalloc -b 4096 -C 65536 /dev/device
+
+Where ``-b`` specifies the block size, ``-C`` specifies the cluster size in bytes,
+and ``-O bigalloc`` enables the bigalloc feature.
+
+Application Interface
+~~~~~~~~~~~~~~~~~~~~~
+
+Applications can use the ``pwritev2()`` system call with the ``RWF_ATOMIC`` flag
+to perform atomic writes:
+
+.. code-block:: c
+
+    pwritev2(fd, iov, iovcnt, offset, RWF_ATOMIC);
+
+The write must be aligned to the filesystem's block size and not exceed the
+filesystem's maximum atomic write unit size.
+See ``generic_atomic_write_valid()`` for more details.
+
+``statx()`` system call with ``STATX_WRITE_ATOMIC`` flag can provides following
+details:
+
+ * ``stx_atomic_write_unit_min``: Minimum size of an atomic write request.
+ * ``stx_atomic_write_unit_max``: Maximum size of an atomic write request.
+ * ``stx_atomic_write_segments_max``: Upper limit for segments. The number of
+   separate memory buffers that can be gathered into a write operation
+   (e.g., the iovcnt parameter for IOV_ITER). Currently, this is always set to one.
+
+The STATX_ATTR_WRITE_ATOMIC flag in ``statx->attributes`` is set if atomic
+writes are supported.
+
+.. _atomic_write_bdev_support:
+
+Hardware Support
+----------------
+
+The underlying storage device must support atomic write operations.
+Modern NVMe and SCSI devices often provide this capability.
+The Linux kernel exposes this information through sysfs:
+
+* ``/sys/block/<device>/queue/atomic_write_unit_min`` - Minimum atomic write size
+* ``/sys/block/<device>/queue/atomic_write_unit_max`` - Maximum atomic write size
+
+Nonzero values for these attributes indicate that the device supports
+atomic writes.
+
+See Also
+--------
+
+* :doc:`bigalloc` - Documentation on the bigalloc feature
+* :doc:`allocators` - Documentation on block allocation in ext4
+* Support for atomic block writes in 6.13:
+  https://lwn.net/Articles/1009298/

Documentation/filesystems/ext4/overview.rst

@@ -25,3 +25,4 @@ order.
 .. include:: inlinedata.rst
 .. include:: eainode.rst
 .. include:: verity.rst
+.. include:: atomic_writes.rst

fs/ext4/bitmap.c

@@ -30,7 +30,7 @@ int ext4_inode_bitmap_csum_verify(struct super_block *sb,
 
 	sz = EXT4_INODES_PER_GROUP(sb) >> 3;
 	provided = le16_to_cpu(gdp->bg_inode_bitmap_csum_lo);
-	calculated = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
+	calculated = ext4_chksum(sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
 	if (sbi->s_desc_size >= EXT4_BG_INODE_BITMAP_CSUM_HI_END) {
 		hi = le16_to_cpu(gdp->bg_inode_bitmap_csum_hi);
 		provided |= (hi << 16);
@@ -52,7 +52,7 @@ void ext4_inode_bitmap_csum_set(struct super_block *sb,
 		return;
 
 	sz = EXT4_INODES_PER_GROUP(sb) >> 3;
-	csum = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
+	csum = ext4_chksum(sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
 	gdp->bg_inode_bitmap_csum_lo = cpu_to_le16(csum & 0xFFFF);
 	if (sbi->s_desc_size >= EXT4_BG_INODE_BITMAP_CSUM_HI_END)
 		gdp->bg_inode_bitmap_csum_hi = cpu_to_le16(csum >> 16);
@@ -71,7 +71,7 @@ int ext4_block_bitmap_csum_verify(struct super_block *sb,
 		return 1;
 
 	provided = le16_to_cpu(gdp->bg_block_bitmap_csum_lo);
-	calculated = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
+	calculated = ext4_chksum(sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
 	if (sbi->s_desc_size >= EXT4_BG_BLOCK_BITMAP_CSUM_HI_END) {
 		hi = le16_to_cpu(gdp->bg_block_bitmap_csum_hi);
 		provided |= (hi << 16);
@@ -92,7 +92,7 @@ void ext4_block_bitmap_csum_set(struct super_block *sb,
 	if (!ext4_has_feature_metadata_csum(sb))
 		return;
 
-	csum = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
+	csum = ext4_chksum(sbi->s_csum_seed, (__u8 *)bh->b_data, sz);
 	gdp->bg_block_bitmap_csum_lo = cpu_to_le16(csum & 0xFFFF);
 	if (sbi->s_desc_size >= EXT4_BG_BLOCK_BITMAP_CSUM_HI_END)
 		gdp->bg_block_bitmap_csum_hi = cpu_to_le16(csum >> 16);