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Re: Directories > 2GB

To: David Chinner <dgc@xxxxxxx>
Subject: Re: Directories > 2GB
From: Steve Lord <lord@xxxxxxx>
Date: Mon, 09 Oct 2006 21:15:28 -0500
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20061010015512.GQ11034@xxxxxxxxxxxxxxxxx>
References: <20061004165655.GD22010@xxxxxxxxxxxxxxxxxxxx> <452AC4BE.6090905@xxxxxxx> <20061010015512.GQ11034@xxxxxxxxxxxxxxxxx>
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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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