linux-kernel - Re: Directories

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Date:	Mon, 09 Oct 2006 21:15:28 -0500
From:	Steve Lord <lord@....org>
To:	David Chinner <dgc@....com>
CC:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, xfs@....sgi.com
Subject: Re: Directories > 2GB

Hi Dave,

My recollection is that it used to default to on, it was disabled
because it needs to map the buffer into a single contiguous chunk
of kernel memory. This was placing a lot of pressure on the memory
remapping code, so we made it not default to on as reworking the
code to deal with non contig memory was looking like a major
effort.

Steve


David Chinner wrote:
> On Mon, Oct 09, 2006 at 04:53:02PM -0500, Steve Lord wrote:
>> You might want to think about keeping the directory a little
>> more contiguous than individual disk blocks. XFS does have
>> code in it to allocate the directory in chunks larger than
>> a single file system block. It does not get used on linux
>> because the code was written under the assumption you can
>> see the whole chunk as a single piece of memory which does not
>> work to well in the linux kernel.
> 
> This code is enabled and seems to work in Linux. I don't know if it
> passes xfsqa  so I don't know how reliable this feature is. TO check
> it all I did was run a quick test on a x86_64 kernel (4k page
> size) using 16k directory blocks (4 pages):



> 
> # mkfs.xfs -f -n size=16384 /dev/ubd/1
> .....
> # xfs_db -r -c "sb 0" -c "p dirblklog" /dev/ubd/1
> dirblklog = 2
> # mount /dev/ubd/1 /mnt/xfs
> # for i in `seq 0 1 100000`; do touch fred.$i; done
> # umount /mnt/xfs
> # mount /mnt/xfs
> # ls /mnt/xfs |wc -l
> 100000
> # rm -rf /mnt/xfs/*
> # ls /mnt/xfs |wc -l
> 0
> # umount /mnt/xfs
> #
> 
> Cheers,
> 
> Dave.

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