Re: [PATCH v17 00/10] mm: introduce memfd_secret system call to create "secret" memory areas
From: Michal Hocko <mhocko@suse.com>
Date: 2021-02-09 09:07:29
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linux-api, linux-arch, linux-fsdevel, linux-kselftest, linux-mm, linux-riscv, lkml, nvdimm
On Mon 08-02-21 22:38:03, David Hildenbrand wrote:
quoted
Am 08.02.2021 um 22:13 schrieb Mike Rapoport [off-list ref]: On Mon, Feb 08, 2021 at 10:27:18AM +0100, David Hildenbrand wrote:quoted
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.
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. -- Michal Hocko SUSE Labs _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel