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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2018-10-24 17:42:24 +0100 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-10-24 17:42:24 +0100 |
| commit | 5993692f09582accb4cb7af11d344598af43c3b8 (patch) | |
| tree | 062447eb44769d6da6e50302853eac1bb1d6e5d3 /Documentation/filesystems/ext4/bigalloc.rst | |
| parent | d6edff78fe9e34dbea1bec7dc26cfce92c6d96d5 (diff) | |
| parent | 33458eaba4dfe778a426df6a19b7aad2ff9f7eec (diff) | |
Merge tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
Pull ext4 updates from Ted Ts'o:
- further restructure ext4 documentation
- fix up ext4's delayed allocation for bigalloc file systems
- fix up some syzbot-detected races in EXT4_IOC_MOVE_EXT,
EXT4_IOC_SWAP_BOOT, and ext4_remount
- ... and a few other miscellaneous bugs and optimizations.
* tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: (21 commits)
ext4: fix use-after-free race in ext4_remount()'s error path
ext4: cache NULL when both default_acl and acl are NULL
docs: promote the ext4 data structures book to top level
docs: move ext4 administrative docs to admin-guide/
jbd2: fix use after free in jbd2_log_do_checkpoint()
ext4: propagate error from dquot_initialize() in EXT4_IOC_FSSETXATTR
ext4: fix setattr project check in fssetxattr ioctl
docs: make ext4 readme tables readable
docs: fix ext4 documentation table formatting problems
docs: generate a separate ext4 pdf file from the documentation
ext4: convert fault handler to use vm_fault_t type
ext4: initialize retries variable in ext4_da_write_inline_data_begin()
ext4: fix EXT4_IOC_SWAP_BOOT
ext4: fix build error when DX_DEBUG is defined
ext4: fix argument checking in EXT4_IOC_MOVE_EXT
ext4: fix reserved cluster accounting at page invalidation time
ext4: adjust reserved cluster count when removing extents
ext4: reduce reserved cluster count by number of allocated clusters
ext4: fix reserved cluster accounting at delayed write time
ext4: add new pending reservation mechanism
...
Diffstat (limited to 'Documentation/filesystems/ext4/bigalloc.rst')
| -rw-r--r-- | Documentation/filesystems/ext4/bigalloc.rst | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext4/bigalloc.rst b/Documentation/filesystems/ext4/bigalloc.rst new file mode 100644 index 000000000000..c6d88557553c --- /dev/null +++ b/Documentation/filesystems/ext4/bigalloc.rst @@ -0,0 +1,22 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Bigalloc +-------- + +At the moment, the default size of a block is 4KiB, which is a commonly +supported page size on most MMU-capable hardware. This is fortunate, as +ext4 code is not prepared to handle the case where the block size +exceeds the page size. However, for a filesystem of mostly huge files, +it is desirable to be able to allocate disk blocks in units of multiple +blocks to reduce both fragmentation and metadata overhead. The +`bigalloc <Bigalloc>`__ feature provides exactly this ability. The +administrator can set a block cluster size at mkfs time (which is stored +in the s\_log\_cluster\_size field in the superblock); from then on, the +block bitmaps track clusters, not individual blocks. This means that +block groups can be several gigabytes in size (instead of just 128MiB); +however, the minimum allocation unit becomes a cluster, not a block, +even for directories. TaoBao had a patchset to extend the “use units of +clusters instead of blocks” to the extent tree, though it is not clear +where those patches went-- they eventually morphed into “extent tree v2” +but that code has not landed as of May 2015. + |