linux-ext4 - Re: [PATCH] ext4: Improve the documentation for ext4's /proc tunables

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Date:	Thu, 9 Oct 2008 10:14:33 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Alex Tomas <bzzz@....com>,
	Andreas Dilger <adilger@....com>
Subject: Re: [PATCH] ext4: Improve the documentation for ext4's /proc
 tunables

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@....edu>
> 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@....edu>
> Cc: Alex Tomas <bzzz@....com>
> Cc: Andreas Dilger <adilger@....com>
> ---
>  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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