Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas

Mike Rapoport
2021-02-11T11:56:12Z

On Thu, Feb 11, 2021 at 11:02:07AM +0100, David Hildenbrand wrote:
>
> Another thought regarding "doesn't have _any_ backing storage"
>
> What are the right semantics when it comes to memory accounting/commit?
>
> As secretmem does not have
> a) any backing storage
> b) cannot go to swap
>
> The MAP_NORESERVE vs. !MAP_NORESERVE handling gets a little unclear. Why
> "reserve swap space" if the allocations cannot ever go to swap? Sure, we
> want to "reserve physical memory", but in contrast to other users that can
> go to swap.
>
> Of course, this is only relevant for MAP_PRIVATE secretmem mappings. Other
> MAP_SHARED assumes there is no need for reserving swap space as it can just
> go to the backing storage. (yeah, tmpfs/shmem is weird in that regard as
> well, but again, it's a bit different)

In that sense seceremem is as weird as tmpfs and it only allows MAP_SHARED.

--
Sincerely yours,
Mike.