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From: Peter Chubb <peter@chubb.wattle.id.au>
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Date: Fri, 5 Jul 2002 15:35:37 +1000
To: reiserfs-dev@namesys.com
Subject: Results of testing Reiserfs on large block devices.
CC: gelato@gelato.unsw.edu.au, linux-kernel@vger.kernel.org
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Hi folks,
   I couldn't get Reiserfs to work on large devices.  I've tracked the
problem down.

  When Reiserfs is mounted, it tries to allocate a chunk of memory for
bitmaps using kmalloc.  The largest chunk allocatable by kmalloc is
128k.  This limits the size of a reiserfs to just under 2TB on a
64-bit platform (16384 bitmaps times 8bytes per pointer) or just under
4TB on a 32 bit platform (32768 bitmaps times 4bytes per pointer).

This reasoning assumes that the number of bitmaps is given by the
formula (number_of_blocks + (8 * blocksize - 1))/(8 * blocksize) where
blocksize is 4096 bytes.  Thus 
	  number_of_blocks = 8 * 4096 * (16384 - 1) - 1  [64 bit]
								
	  number_of_blocks = 8 * 4096 * (32768 - 1) - 1  [32 bit]

Hacking mm/slab.c to increase the memory limit allowed larger
filesystems to be mounted, but I haven't tested these thoroughly yet.
--
Dr Peter Chubb				    peterc@gelato.unsw.edu.au
You are lost in a maze of BitKeeper repositories, all almost the same.

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