Documentation/filesystems/ext4/overview.rst

File Facts

System

Linux kernel

Corpus path

Documentation/filesystems/ext4/overview.rst

Extension

.rst

Size

930 bytes

Lines

31

Domain

Support Tooling And Documentation

Bucket

Documentation

Inferred role

Support Tooling And Documentation: documentation

Status

atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

• Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
• Uses kernel synchronization; read lock ordering, sleepability, and interrupt context assumptions before translating.

Dependency Surface

• No C-style include directives detected by the generator.

Detected Declarations

• No top-level syscall, struct, function, initcall, or export declaration detected by the generator.

Annotated Snippet

.. SPDX-License-Identifier: GPL-2.0

High Level Design
=================

An ext4 file system is split into a series of block groups. To reduce
performance difficulties due to fragmentation, the block allocator tries
very hard to keep each file's blocks within the same group, thereby
reducing seek times. The size of a block group is specified in
``sb.s_blocks_per_group`` blocks, though it can also calculated as 8 *
``block_size_in_bytes``. With the default block size of 4KiB, each group
will contain 32,768 blocks, for a length of 128MiB. The number of block
groups is the size of the device divided by the size of a block group.

All fields in ext4 are written to disk in little-endian order. HOWEVER,
all fields in jbd2 (the journal) are written to disk in big-endian
order.

.. toctree::

   blocks
   blockgroup
   special_inodes
   allocators
   checksums
   bigalloc
   inlinedata
   eainode
   verity
   atomic_writes

Annotation

• Atlas domain: Support Tooling And Documentation / Documentation.
• Implementation status: atlas-only.
• Synchronization appears in or near this file; preserve lock ordering, sleepability, and interrupt-context constraints.

Implementation Notes

• This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
• Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
• Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.