Message-ID: <48d0b46e-2b82-44b6-a717-94bc258a508d@linux.dev>
Date: Mon, 8 Dec 2025 20:43:22 -0800
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: Pratyush Yadav <pratyush@...nel.org>,
 Pasha Tatashin <pasha.tatashin@...een.com>, Mike Rapoport <rppt@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, Jonathan Corbet <corbet@....net>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Muchun Song <muchun.song@...ux.dev>, Oscar Salvador <osalvador@...e.de>,
 Alexander Graf <graf@...zon.com>, David Matlack <dmatlack@...gle.com>,
 David Rientjes <rientjes@...gle.com>, Jason Gunthorpe <jgg@...dia.com>,
 Samiullah Khawaja <skhawaja@...gle.com>, Vipin Sharma <vipinsh@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [RFC PATCH 00/10] liveupdate: hugetlb support


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 out-of-date.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

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