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Subject: Re: [PATCH 06/10] AXFS: axfs_super.c
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> From this it would appear that if the region data can't be mapped XIP (i.e.
> it is compressed or on a block device), it is cached in its entirety in RAM?

That is correct.

> This implies for block devices that the entire filesystem metadata has to be
> cached in RAM.  This severely limits the size of AXFS filesystems when using
> block devices, or the else memory usage will be excessive.

This is where 64bit squashfs could be a better fit.