ext4: update ext4 documentation
Add documentation for mount options and ioctls to Documentation/filesystem/ext4.txt, which has not been udpated for some time. Also add for ext4 sysfs tunables to the Documentation/ABI/testing/sysfs-fs-ext4 file, and fix a few typographical errors in that file. https://bugzilla.kernel.org/show_bug.cgi?id=9423 Signed-off-by: Lukas Czerner <lczerner@redhat.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Lukas Czerner
Theodore Ts'o
parent
3abb17e82f
commit
6f9524e9e1
@ -48,7 +48,7 @@ Description:
|
||||
will have its blocks allocated out of its own unique
|
||||
preallocation pool.
|
||||
|
||||
What: /sys/fs/ext4/<disk>/inode_readahead
|
||||
What: /sys/fs/ext4/<disk>/inode_readahead_blks
|
||||
Date: March 2008
|
||||
Contact: "Theodore Ts'o" <tytso@mit.edu>
|
||||
Description:
|
||||
@ -85,7 +85,14 @@ Date: June 2008
|
||||
Contact: "Theodore Ts'o" <tytso@mit.edu>
|
||||
Description:
|
||||
Tuning parameter which (if non-zero) controls the goal
|
||||
inode used by the inode allocator in p0reference to
|
||||
all other allocation hueristics. This is intended for
|
||||
inode used by the inode allocator in preference to
|
||||
all other allocation heuristics. This is intended for
|
||||
debugging use only, and should be 0 on production
|
||||
systems.
|
||||
|
||||
What: /sys/fs/ext4/<disk>/max_writeback_mb_bump
|
||||
Date: September 2009
|
||||
Contact: "Theodore Ts'o" <tytso@mit.edu>
|
||||
Description:
|
||||
The maximum number of megabytes the writeback code will
|
||||
try to write out before move on to another inode.
|
||||
|
||||
@ -367,12 +367,47 @@ init_itable=n The lazy itable init code will wait n times the
|
||||
minimizes the impact on the systme performance
|
||||
while file system's inode table is being initialized.
|
||||
|
||||
discard Controls whether ext4 should issue discard/TRIM
|
||||
discard Controls whether ext4 should issue discard/TRIM
|
||||
nodiscard(*) commands to the underlying block device when
|
||||
blocks are freed. This is useful for SSD devices
|
||||
and sparse/thinly-provisioned LUNs, but it is off
|
||||
by default until sufficient testing has been done.
|
||||
|
||||
nouid32 Disables 32-bit UIDs and GIDs. This is for
|
||||
interoperability with older kernels which only
|
||||
store and expect 16-bit values.
|
||||
|
||||
resize Allows to resize filesystem to the end of the last
|
||||
existing block group, further resize has to be done
|
||||
with resize2fs either online, or offline. It can be
|
||||
used only with conjunction with remount.
|
||||
|
||||
block_validity This options allows to enables/disables the in-kernel
|
||||
noblock_validity facility for tracking filesystem metadata blocks
|
||||
within internal data structures. This allows multi-
|
||||
block allocator and other routines to quickly locate
|
||||
extents which might overlap with filesystem metadata
|
||||
blocks. This option is intended for debugging
|
||||
purposes and since it negatively affects the
|
||||
performance, it is off by default.
|
||||
|
||||
dioread_lock Controls whether or not ext4 should use the DIO read
|
||||
dioread_nolock locking. If the dioread_nolock option is specified
|
||||
ext4 will allocate uninitialized extent before buffer
|
||||
write and convert the extent to initialized after IO
|
||||
completes. This approach allows ext4 code to avoid
|
||||
using inode mutex, which improves scalability on high
|
||||
speed storages. However this does not work with nobh
|
||||
option and the mount will fail. Nor does it work with
|
||||
data journaling and dioread_nolock option will be
|
||||
ignored with kernel warning. Note that dioread_nolock
|
||||
code path is only used for extent-based files.
|
||||
Because of the restrictions this options comprises
|
||||
it is off by default (e.g. dioread_lock).
|
||||
|
||||
i_version Enable 64-bit inode version support. This option is
|
||||
off by default.
|
||||
|
||||
Data Mode
|
||||
=========
|
||||
There are 3 different data modes:
|
||||
@ -400,6 +435,176 @@ needs to be read from and written to disk at the same time where it
|
||||
outperforms all others modes. Currently ext4 does not have delayed
|
||||
allocation support if this data journalling mode is selected.
|
||||
|
||||
/proc entries
|
||||
=============
|
||||
|
||||
Information about mounted ext4 file systems can be found in
|
||||
/proc/fs/ext4. Each mounted filesystem will have a directory in
|
||||
/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
|
||||
/proc/fs/ext4/dm-0). The files in each per-device directory are shown
|
||||
in table below.
|
||||
|
||||
Files in /proc/fs/ext4/<devname>
|
||||
..............................................................................
|
||||
File Content
|
||||
mb_groups details of multiblock allocator buddy cache of free blocks
|
||||
..............................................................................
|
||||
|
||||
/sys entries
|
||||
============
|
||||
|
||||
Information about mounted ext4 file systems can be found in
|
||||
/sys/fs/ext4. Each mounted filesystem will have a directory in
|
||||
/sys/fs/ext4 based on its device name (i.e., /sys/fs/ext4/hdc or
|
||||
/sys/fs/ext4/dm-0). The files in each per-device directory are shown
|
||||
in table below.
|
||||
|
||||
Files in /sys/fs/ext4/<devname>
|
||||
(see also Documentation/ABI/testing/sysfs-fs-ext4)
|
||||
..............................................................................
|
||||
File Content
|
||||
|
||||
delayed_allocation_blocks This file is read-only and shows the number of
|
||||
blocks that are dirty in the page cache, but
|
||||
which do not have their location in the
|
||||
filesystem allocated yet.
|
||||
|
||||
inode_goal Tuning parameter which (if non-zero) controls
|
||||
the goal inode used by the inode allocator in
|
||||
preference to all other allocation heuristics.
|
||||
This is intended for debugging use only, and
|
||||
should be 0 on production systems.
|
||||
|
||||
inode_readahead_blks Tuning parameter which controls the maximum
|
||||
number of inode table blocks that ext4's inode
|
||||
table readahead algorithm will pre-read into
|
||||
the buffer cache
|
||||
|
||||
lifetime_write_kbytes This file is read-only and shows the number of
|
||||
kilobytes of data that have been written to this
|
||||
filesystem since it was created.
|
||||
|
||||
max_writeback_mb_bump The maximum number of megabytes the writeback
|
||||
code will try to write out before move on to
|
||||
another inode.
|
||||
|
||||
mb_group_prealloc The multiblock allocator will round up allocation
|
||||
requests to a multiple of this tuning parameter if
|
||||
the stripe size is not set in the ext4 superblock
|
||||
|
||||
mb_max_to_scan The maximum number of extents the multiblock
|
||||
allocator will search to find the best extent
|
||||
|
||||
mb_min_to_scan The minimum number of extents the multiblock
|
||||
allocator will search to find the best extent
|
||||
|
||||
mb_order2_req Tuning parameter which controls the minimum size
|
||||
for requests (as a power of 2) where the buddy
|
||||
cache is used
|
||||
|
||||
mb_stats Controls whether the multiblock allocator should
|
||||
collect statistics, which are shown during the
|
||||
unmount. 1 means to collect statistics, 0 means
|
||||
not to collect statistics
|
||||
|
||||
mb_stream_req Files which have fewer blocks than this tunable
|
||||
parameter will have their blocks allocated out
|
||||
of a block group specific preallocation pool, so
|
||||
that small files are packed closely together.
|
||||
Each large file will have its blocks allocated
|
||||
out of its own unique preallocation pool.
|
||||
|
||||
session_write_kbytes This file is read-only and shows the number of
|
||||
kilobytes of data that have been written to this
|
||||
filesystem since it was mounted.
|
||||
..............................................................................
|
||||
|
||||
Ioctls
|
||||
======
|
||||
|
||||
There is some Ext4 specific functionality which can be accessed by applications
|
||||
through the system call interfaces. The list of all Ext4 specific ioctls are
|
||||
shown in the table below.
|
||||
|
||||
Table of Ext4 specific ioctls
|
||||
..............................................................................
|
||||
Ioctl Description
|
||||
EXT4_IOC_GETFLAGS Get additional attributes associated with inode.
|
||||
The ioctl argument is an integer bitfield, with
|
||||
bit values described in ext4.h. This ioctl is an
|
||||
alias for FS_IOC_GETFLAGS.
|
||||
|
||||
EXT4_IOC_SETFLAGS Set additional attributes associated with inode.
|
||||
The ioctl argument is an integer bitfield, with
|
||||
bit values described in ext4.h. This ioctl is an
|
||||
alias for FS_IOC_SETFLAGS.
|
||||
|
||||
EXT4_IOC_GETVERSION
|
||||
EXT4_IOC_GETVERSION_OLD
|
||||
Get the inode i_generation number stored for
|
||||
each inode. The i_generation number is normally
|
||||
changed only when new inode is created and it is
|
||||
particularly useful for network filesystems. The
|
||||
'_OLD' version of this ioctl is an alias for
|
||||
FS_IOC_GETVERSION.
|
||||
|
||||
EXT4_IOC_SETVERSION
|
||||
EXT4_IOC_SETVERSION_OLD
|
||||
Set the inode i_generation number stored for
|
||||
each inode. The '_OLD' version of this ioctl
|
||||
is an alias for FS_IOC_SETVERSION.
|
||||
|
||||
EXT4_IOC_GROUP_EXTEND This ioctl has the same purpose as the resize
|
||||
mount option. It allows to resize filesystem
|
||||
to the end of the last existing block group,
|
||||
further resize has to be done with resize2fs,
|
||||
either online, or offline. The argument points
|
||||
to the unsigned logn number representing the
|
||||
filesystem new block count.
|
||||
|
||||
EXT4_IOC_MOVE_EXT Move the block extents from orig_fd (the one
|
||||
this ioctl is pointing to) to the donor_fd (the
|
||||
one specified in move_extent structure passed
|
||||
as an argument to this ioctl). Then, exchange
|
||||
inode metadata between orig_fd and donor_fd.
|
||||
This is especially useful for online
|
||||
defragmentation, because the allocator has the
|
||||
opportunity to allocate moved blocks better,
|
||||
ideally into one contiguous extent.
|
||||
|
||||
EXT4_IOC_GROUP_ADD Add a new group descriptor to an existing or
|
||||
new group descriptor block. The new group
|
||||
descriptor is described by ext4_new_group_input
|
||||
structure, which is passed as an argument to
|
||||
this ioctl. This is especially useful in
|
||||
conjunction with EXT4_IOC_GROUP_EXTEND,
|
||||
which allows online resize of the filesystem
|
||||
to the end of the last existing block group.
|
||||
Those two ioctls combined is used in userspace
|
||||
online resize tool (e.g. resize2fs).
|
||||
|
||||
EXT4_IOC_MIGRATE This ioctl operates on the filesystem itself.
|
||||
It converts (migrates) ext3 indirect block mapped
|
||||
inode to ext4 extent mapped inode by walking
|
||||
through indirect block mapping of the original
|
||||
inode and converting contiguous block ranges
|
||||
into ext4 extents of the temporary inode. Then,
|
||||
inodes are swapped. This ioctl might help, when
|
||||
migrating from ext3 to ext4 filesystem, however
|
||||
suggestion is to create fresh ext4 filesystem
|
||||
and copy data from the backup. Note, that
|
||||
filesystem has to support extents for this ioctl
|
||||
to work.
|
||||
|
||||
EXT4_IOC_ALLOC_DA_BLKS Force all of the delay allocated blocks to be
|
||||
allocated to preserve application-expected ext3
|
||||
behaviour. Note that this will also start
|
||||
triggering a write of the data blocks, but this
|
||||
behaviour may change in the future as it is
|
||||
not necessary and has been done this way only
|
||||
for sake of simplicity.
|
||||
..............................................................................
|
||||
|
||||
References
|
||||
==========
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user