While it is true that e2fsck does not free memory during operation, in
practice this is not a problem. Even for large filesystems (say 32-48TB)
it will only use around 8-12GB of RAM so that is very reasonable for a
server today. 

The rough estimate that I use for e2fsck is 1 byte of RAM per block. 

Cheers, Andreas

On Mar 21, 2017, at 16:07, Manish Katiyar [off-list ref] wrote:

Hi,

I was looking at e2fsck code to see if there are any limits on running
e2fsck on large ext4 filesystems. From the code it looks like all the
required metadata while e2fsck is running is only kept in memory and
is only flushed to disk when the appropriate changes are corrected.
(Except the undo file case).
There doesn't seem to be a case/code where we have to periodically
flush some tracking metadata while it is running, just because we have
too much of incore tracking data and may ran out of memory (looks like
code will simply return failure if ext2fs_get_mem() returns failure)

Appreciate if someone can confirm that my understanding is correct ?

Thanks -
Manish