Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing mirroring functionality

From: Anshuman Khandual
Date: Fri Jul 07 2017 - 04:47:19 EST

On 07/06/2017 09:47 PM, Mike Kravetz wrote:
> The mremap system call has the ability to 'mirror' parts of an existing
> mapping. To do so, it creates a new mapping that maps the same pages as
> the original mapping, just at a different virtual address. This
> functionality has existed since at least the 2.6 kernel.
> This patch simply adds a new flag to mremap which will make this
> functionality part of the API. It maintains backward compatibility with
> the existing way of requesting mirroring (old_size == 0).
> If this new MREMAP_MIRROR flag is specified, then new_size must equal
> old_size. In addition, the MREMAP_MAYMOVE flag must be specified.

Yeah it all looks good. But why is this requirement that if
MREMAP_MAYMOVE is specified then old_size and new_size must
be equal.