On Mon 08-02-21 22:38:03, David Hildenbrand wrote:
Am 08.02.2021 um 22:13 schrieb Mike Rapoport rppt@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:
- How will the issue of plenty of unmovable allocations for user space be
tackled in the future?
- 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.
A lot of unevictable memory is a concern regardless of CMA/ZONE_MOVABLE. As I've said it is quite easy to land at the similar situation even with tmpfs/MAP_ANON|MAP_SHARED on swapless system. Neither of the two is really uncommon. It would be even worse that those would be allowed to consume both CMA/ZONE_MOVABLE.
One has to be very careful when relying on CMA or movable zones. This is definitely worth a comment in the kernel command line parameter documentation. But this is not a new problem.