Re: [RFC PATCH 00/10] liveupdate: hugetlb support

Zhu Yanjun
2025-12-09T04:43:44Z

在 2025/12/6 15:02, Pratyush Yadav 写道:
> 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 out-of-date.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.

Is this patch serise based on the patches in the link
https://lkml.org/lkml/2025/11/26/1665?

Thanks,

Yanjun.Zhu

>
> 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/20251125165850.3389713-1-pasha.tatashin@soleen.com/T/#u
> [1] https://lwn.net/Articles/1033364/
> [2] https://lore.kernel.org/linux-mm/20251125225006.3722394-1-pasha.tatashin@soleen.com/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

--
Best Regards,
Yanjun.Zhu