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Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4

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* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: (61 commits)
  ext4: Documention update for new ordered mode and delayed allocation
  ext4: do not set extents feature from the kernel
  ext4: Don't allow nonextenst mount option for large filesystem
  ext4: Enable delalloc by default.
  ext4: delayed allocation i_blocks fix for stat
  ext4: fix delalloc i_disksize early update issue
  ext4: Handle page without buffers in ext4_*_writepage()
  ext4: Add ordered mode support for delalloc
  ext4: Invert lock ordering of page_lock and transaction start in delalloc
  mm: Add range_cont mode for writeback
  ext4: delayed allocation ENOSPC handling
  percpu_counter: new function percpu_counter_sum_and_set
  ext4: Add delayed allocation support in data=writeback mode
  vfs: add hooks for ext4's delayed allocation support
  jbd2: Remove data=ordered mode support using jbd buffer heads
  ext4: Use new framework for data=ordered mode in JBD2
  jbd2: Implement data=ordered mode handling via inodes
  vfs: export filemap_fdatawrite_range()
  ext4: Fix lock inversion in ext4_ext_truncate()
  ext4: Invert the locking order of page_lock and transaction start
  ...
This commit is contained in:
Linus Torvalds 2008-07-15 08:36:38 -07:00
commit 8d2567a620
35 changed files with 2845 additions and 1082 deletions
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125
Documentation/filesystems/ext4.txt
View file

@ -13,72 +13,93 @@ Mailing list: [email protected]
1. Quick usage instructions:
===========================
- Grab updated e2fsprogs from
ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs-interim/
This is a patchset on top of e2fsprogs-1.39, which can be found at
- Compile and install the latest version of e2fsprogs (as of this
writing version 1.41) from:
http://sourceforge.net/project/showfiles.php?group_id=2406
or
ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/
- It's still mke2fs -j /dev/hda1
or grab the latest git repository from:
- mount /dev/hda1 /wherever -t ext4dev
git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
- To enable extents,
- Create a new filesystem using the ext4dev filesystem type:
mount /dev/hda1 /wherever -t ext4dev -o extents
# mke2fs -t ext4dev /dev/hda1
- The filesystem is compatible with the ext3 driver until you add a file
which has extents (ie: `mount -o extents', then create a file).
Or configure an existing ext3 filesystem to support extents and set
the test_fs flag to indicate that it's ok for an in-development
filesystem to touch this filesystem:
NOTE: The "extents" mount flag is temporary. It will soon go away and
extents will be enabled by the "-o extents" flag to mke2fs or tune2fs
# tune2fs -O extents -E test_fs /dev/hda1
If the filesystem was created with 128 byte inodes, it can be
converted to use 256 byte for greater efficiency via:
# tune2fs -I 256 /dev/hda1
(Note: we currently do not have tools to convert an ext4dev
filesystem back to ext3; so please do not do try this on production
filesystems.)
- Mounting:
# mount -t ext4dev /dev/hda1 /wherever
- When comparing performance with other filesystems, remember that
ext3/4 by default offers higher data integrity guarantees than most. So
when comparing with a metadata-only journalling filesystem, use `mount -o
data=writeback'. And you might as well use `mount -o nobh' too along
with it. Making the journal larger than the mke2fs default often helps
performance with metadata-intensive workloads.
ext3/4 by default offers higher data integrity guarantees than most.
So when comparing with a metadata-only journalling filesystem, such
as ext3, use `mount -o data=writeback'. And you might as well use
`mount -o nobh' too along with it. Making the journal larger than
the mke2fs default often helps performance with metadata-intensive
workloads.
2. Features
===========
2.1 Currently available
* ability to use filesystems > 16TB
* ability to use filesystems > 16TB (e2fsprogs support not available yet)
* extent format reduces metadata overhead (RAM, IO for access, transactions)
* extent format more robust in face of on-disk corruption due to magics,
* internal redunancy in tree
2.1 Previously available, soon to be enabled by default by "mkefs.ext4":
* dir_index and resize inode will be on by default
* large inodes will be used by default for fast EAs, nsec timestamps, etc
* improved file allocation (multi-block alloc)
* fix 32000 subdirectory limit
* nsec timestamps for mtime, atime, ctime, create time
* inode version field on disk (NFSv4, Lustre)
* reduced e2fsck time via uninit_bg feature
* journal checksumming for robustness, performance
* persistent file preallocation (e.g for streaming media, databases)
* ability to pack bitmaps and inode tables into larger virtual groups via the
flex_bg feature
* large file support
* Inode allocation using large virtual block groups via flex_bg
* delayed allocation
* large block (up to pagesize) support
* efficent new ordered mode in JBD2 and ext4(avoid using buffer head to force
the ordering)
2.2 Candidate features for future inclusion
There are several under discussion, whether they all make it in is
partly a function of how much time everyone has to work on them:
* Online defrag (patches available but not well tested)
* reduced mke2fs time via lazy itable initialization in conjuction with
the uninit_bg feature (capability to do this is available in e2fsprogs
but a kernel thread to do lazy zeroing of unused inode table blocks
after filesystem is first mounted is required for safety)
* improved file allocation (multi-block alloc, delayed alloc; basically done)
* fix 32000 subdirectory limit (patch exists, needs some e2fsck work)
* nsec timestamps for mtime, atime, ctime, create time (patch exists,
needs some e2fsck work)
* inode version field on disk (NFSv4, Lustre; prototype exists)
* reduced mke2fs/e2fsck time via uninitialized groups (prototype exists)
* journal checksumming for robustness, performance (prototype exists)
* persistent file preallocation (e.g for streaming media, databases)
There are several others under discussion, whether they all make it in is
partly a function of how much time everyone has to work on them. Features like
metadata checksumming have been discussed and planned for a bit but no patches
exist yet so I'm not sure they're in the near-term roadmap.
Features like metadata checksumming have been discussed and planned for
a bit but no patches exist yet so I'm not sure they're in the near-term
roadmap.
The big performance win will come with mballoc, delalloc and flex_bg
grouping of bitmaps and inode tables. Some test results available here:
The big performance win will come with mballoc and delalloc. CFS has
been using mballoc for a few years already with Lustre, and IBM + Bull
did a lot of benchmarking on it. The reason it isn't in the first set of
patches is partly a manageability issue, and partly because it doesn't
directly affect the on-disk format (outside of much better allocation)
so it isn't critical to get into the first round of changes. I believe
Alex is working on a new set of patches right now.
- http://www.bullopensource.org/ext4/20080530/ffsb-write-2.6.26-rc2.html
- http://www.bullopensource.org/ext4/20080530/ffsb-readwrite-2.6.26-rc2.html
3. Options
==========
@ -222,9 +243,11 @@ stripe=n Number of filesystem blocks that mballoc will try
to use for allocation size and alignment. For RAID5/6
systems this should be the number of data
disks * RAID chunk size in file system blocks.
delalloc (*) Deferring block allocation until write-out time.
nodelalloc Disable delayed allocation. Blocks are allocation
when data is copied from user to page cache.
Data Mode
---------
=========
There are 3 different data modes:
* writeback mode
@ -236,10 +259,10 @@ typically provide the best ext4 performance.
* ordered mode
In data=ordered mode, ext4 only officially journals metadata, but it logically
groups metadata and data blocks into a single unit called a transaction. When
it's time to write the new metadata out to disk, the associated data blocks
are written first. In general, this mode performs slightly slower than
writeback but significantly faster than journal mode.
groups metadata information related to data changes with the data blocks into a
single unit called a transaction. When it's time to write the new metadata
out to disk, the associated data blocks are written first. In general,
this mode performs slightly slower than writeback but significantly faster than journal mode.
* journal mode
data=journal mode provides full data and metadata journaling. All new data is
@ -247,7 +270,8 @@ written to the journal first, and then to its final location.
In the event of a crash, the journal can be replayed, bringing both data and
metadata into a consistent state. This mode is the slowest except when data
needs to be read from and written to disk at the same time where it
outperforms all others modes.
outperforms all others modes. Curently ext4 does not have delayed
allocation support if this data journalling mode is selected.
References
==========
@ -256,7 +280,8 @@ kernel source: <file:fs/ext4/>
<file:fs/jbd2/>
programs: http://e2fsprogs.sourceforge.net/
http://ext2resize.sourceforge.net
useful links: http://fedoraproject.org/wiki/ext3-devel
http://www.bullopensource.org/ext4/
http://ext4.wiki.kernel.org/index.php/Main_Page
http://fedoraproject.org/wiki/Features/Ext4