2GB memory limit running fsck on a +6TB device

Carlo Wood carlo at alinoe.com
Mon Jun 9 22:08:56 UTC 2008

On Mon, Jun 09, 2008 at 03:50:32PM -0600, Andreas Dilger wrote:
> > Running fsck with a 64bit LiveCD will solve the problem?
> Yes, I suspect with a 64-bit kernel you could allocate the full 4GB of RAM
> for e2fsck and be able to check the filesystem.

We had a simular problem with ext3grep.
You have to realize that every mmap uses memory
address space, even if it's a map to disk.
Therefore, on a 32bit machine, if the total
of all normal allocations plus all simultaneous
mmap's exceeds 4GB then you "run out of memory",
even if -say- only 1 GB is really allocated
and >3GB of the disk is mmap-ed.

In that case a 64bit machine would solve the
problem because then all ram (2 GB I read in
the Subject) can be used for normal allocations
while any disk mmap has cazillion address space
left for itself.

Carlo Wood <carlo at alinoe.com>

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