[PATCH v17 00/10] mm: introduce memfd_secret system call to create "secret" memory areas

[David Hildenbrand]

> Am 08.02.2021 um 22:13 schrieb Mike Rapoport <rppt at kernel.org>:
> 
> On Mon, Feb 08, 2021 at 10:27:18AM +0100, David Hildenbrand wrote:
>> On 08.02.21 09:49, Mike Rapoport wrote:
>> 
>> Some questions (and request to document the answers) as we now allow to have
>> unmovable allocations all over the place and I don't see a single comment
>> regarding that in the cover letter:
>> 
>> 1. How will the issue of plenty of unmovable allocations for user space be
>> tackled in the future?
>> 
>> 2. How has this issue been documented? E.g., interaction with ZONE_MOVABLE
>> and CMA, alloc_conig_range()/alloc_contig_pages?.
> 
> Secretmem sets the mappings gfp mask to GFP_HIGHUSER, so it does not
> allocate movable pages at the first place.

That is not the point. Secretmem cannot go on CMA / ZONE_MOVABLE memory and behaves like long-term pinnings in that sense. This is a real issue when using a lot of sectremem.

Please have a look at what Pavel documents regarding long term pinnings and ZONE_MOVABLE in his patches currently on the list.