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Date:   Thu, 11 Feb 2021 13:29:46 +0200
From:   Mike Rapoport <rppt@kernel.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     Michal Hocko <mhocko@suse.com>, Mike Rapoport <rppt@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
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        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
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Subject: Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to
 create "secret" memory areas
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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.