On Thu, 09 Oct 2008 12:49:26 -0400 Theodore Ts'o wrote:
> >From be75f52f5e9acd376c64ff41f84314213bb761bb Mon Sep 17 00:00:00 2001
> From: Theodore Ts'o <tytso@xxxxxxx>
> Date: Thu, 9 Oct 2008 12:48:49 -0400
> Subject: [PATCH] ext4: Improve the documentation for ext4's /proc tunables
>
> Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> Cc: Alex Tomas <bzzz@xxxxxxx>
> Cc: Andreas Dilger <adilger@xxxxxxx>
> ---
> Documentation/filesystems/proc.txt | 70 +++++++++++++++++-------------------
> 1 files changed, 33 insertions(+), 37 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index f566ad9..bcf742d 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -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
> -
> -mb_history:
> -Multiblock allocation history.
> -
> -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.
> +
> +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.
> +
> +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 minum number of extents the multiblock allocator
minimum
> + 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 files
file
> + will have its blocks allocated out of its own unique
> + preallocation pool.
> +..............................................................................
> +
---
~Randy
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