This series adds support for live updating hugetlb-backed memfd, including support for 1G huge pages. This allows live updating VMs which use hugepages to back VM memory.
Please take a look at this patch series [0] to know more about the Live Update Orchestrator (LUO). It also includes patches for live updating a shmem-backed memfd. This series is a follow up to that, adding huge page support as well. You can also read this LWN article [1] to learn more about KHO and Live Update Orchestrator, though do note that this article is a bit out-of-date. LUO has since evolved. For example, subsystems have been replaced with FLB, and the state machine has been simplified. This series is based on top of mm-non-unstable, which includes the LUO FLB patches [2]. This series uses LUO FLB to track how many pages are preserved for each hstate, to ensure the live updated kernel does not over-allocate hugepages. Areas for Discussion ==================== Why is this an RFC? ------------------- While I believe the code is in decent shape, I have only done some basic testing and have not put it through more intensive testing, including testing on ARM64. I am also not completely confident on the handling of reservations and cgroup charging, even though it appears to work on the surface. The goal of this is to start discussion at high level points so we can at least agree on the general direction. This also gives people some time to see the code, before the session discussing this at LPC 2025 [3]. Disabling scratch-only earlier in boot -------------------------------------- Patch 2 moves KHO memory initialization to earlier in boot. Detailed discussion on the topic is in patch 2's message. Allocating gigantic hugepages after paging_init() on x86 -------------------------------------------------------- To allow KHO to work with gigantic hugepages on x86, patch 2 moves gigantic huge page allocation after paging_init(). This can have some impact on ability to allocate gigantic pages, but I believe the impact should not be severe. See patch 2 for more detailed discussion and test results. Early-boot access to LUO FLB data --------------------------------- To work with gigantic page allocation, LUO FLB data is needed in early boot, before LUO is fully initialized. Patch 3 adds support for fetching LUO FLB data in early boot. Preserving the entire huge page pool vs only used ------------------------------------------------- This series makes a design decision on preserving only the number of preserved huge pages for each hstate, instead of preserving the entire huge page pool. Both approaches were brought up in the Live Update meetings. Patch 6 discusses the reasoning in more detail. [0] https://lore.kernel.org/linux-mm/[email protected]/T/#u [1] https://lwn.net/Articles/1033364/ [2] https://lore.kernel.org/linux-mm/[email protected]/T/#u [3] https://lpc.events/event/19/contributions/2044/ Pratyush Yadav (10): kho: drop restriction on maximum page order kho: disable scratch-only earlier in boot liveupdate: do early initialization before hugepages are allocated liveupdate: flb: allow getting FLB data in early boot mm: hugetlb: export some functions to hugetlb-internal header liveupdate: hugetlb subsystem FLB state preservation mm: hugetlb: don't allocate pages already in live update mm: hugetlb: disable CMA if liveupdate is enabled mm: hugetlb: allow freezing the inode liveupdate: allow preserving hugetlb-backed memfd Documentation/mm/memfd_preservation.rst | 9 + MAINTAINERS | 2 + arch/x86/kernel/setup.c | 19 +- fs/hugetlbfs/inode.c | 14 +- include/linux/hugetlb.h | 8 + include/linux/kho/abi/hugetlb.h | 98 ++++ include/linux/liveupdate.h | 12 + kernel/liveupdate/Kconfig | 15 + kernel/liveupdate/kexec_handover.c | 13 +- kernel/liveupdate/luo_core.c | 30 +- kernel/liveupdate/luo_flb.c | 69 ++- kernel/liveupdate/luo_internal.h | 2 + mm/Makefile | 1 + mm/hugetlb.c | 113 ++-- mm/hugetlb_cma.c | 7 + mm/hugetlb_internal.h | 50 ++ mm/hugetlb_luo.c | 699 ++++++++++++++++++++++++ mm/memblock.c | 1 - mm/memfd_luo.c | 4 - mm/mm_init.c | 15 +- 20 files changed, 1099 insertions(+), 82 deletions(-) create mode 100644 include/linux/kho/abi/hugetlb.h create mode 100644 mm/hugetlb_internal.h create mode 100644 mm/hugetlb_luo.c base-commit: 55b7d75112c25b3e2a5eadc11244c330a5c00a41 -- 2.43.0
