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ext4: Improve the documentation for ext4's /proc tunables 

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Alex Tomas <bzzz@sun.com>
Cc: Andreas Dilger <adilger@sun.com>
This commit is contained in:
Theodore Ts'o 2008-10-09 23:21:54 -04:00
parent 5e8814f2f7
commit 37515facd0
1 changed files with 30 additions and 34 deletions
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64
Documentation/filesystems/proc.txt
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@ -923,45 +923,41 @@ CPUs.
The "procs_blocked" line gives the number of processes currently blocked,
waiting for I/O to complete.
1.9 Ext4 file system parameters
------------------------------
Ext4 file system have one directory per partition under /proc/fs/ext4/
# ls /proc/fs/ext4/hdc/
group_prealloc max_to_scan mb_groups mb_history min_to_scan order2_req
stats stream_req
mb_groups:
This file gives the details of multiblock allocator buddy cache of free blocks
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 1-10, below.
mb_history:
Multiblock allocation history.
Table 1-10: Files in /proc/fs/ext4/<devname>
..............................................................................
File Content
mb_groups details of multiblock allocator buddy cache of free blocks
mb_history multiblock allocation history
stats controls whether the multiblock allocator should start
collecting statistics, which are shown during the unmount
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
max_to_scan The maximum number of extents the multiblock allocator
will search to find the best extent
min_to_scan The minimum number of extents the multiblock allocator
will search to find the best extent
order2_req Tuning parameter which controls the minimum size for
requests (as a power of 2) where the buddy cache is
used
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.
..............................................................................
stats:
This file indicate whether the multiblock allocator should start collecting
statistics. The statistics are shown during unmount
group_prealloc:
The multiblock allocator normalize the block allocation request to
group_prealloc filesystem blocks if we don't have strip value set.
The stripe value can be specified at mount time or during mke2fs.
max_to_scan:
How long multiblock allocator can look for a best extent (in found extents)
min_to_scan:
How long multiblock allocator must look for a best extent
order2_req:
Multiblock allocator use 2^N search using buddies only for requests greater
than or equal to order2_req. The request size is specfied in file system
blocks. A value of 2 indicate only if the requests are greater than or equal
to 4 blocks.
stream_req:
Files smaller than stream_req are served by the stream allocator, whose
purpose is to pack requests as close each to other as possible to
produce smooth I/O traffic. Avalue of 16 indicate that file smaller than 16
filesystem block size will use group based preallocation.
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Summary