linux-kernel - Re: [PATCH 0/5] prctl: extend PR_SET_THP_DISABLE to only provide THPs when advised

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Message-ID: <399a8c3a-3966-4430-bb74-f2d2ece99ea9@lucifer.local>
Date: Thu, 31 Jul 2025 13:24:22 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, corbet@....net,
        rppt@...nel.org, surenb@...gle.com, mhocko@...e.com,
        hannes@...xchg.org, baohua@...nel.org, shakeel.butt@...ux.dev,
        riel@...riel.com, ziy@...dia.com, laoar.shao@...il.com,
        dev.jain@....com, baolin.wang@...ux.alibaba.com, npache@...hat.com,
        Liam.Howlett@...cle.com, ryan.roberts@....com, vbabka@...e.cz,
        jannh@...gle.com, Arnd Bergmann <arnd@...db.de>, sj@...nel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...a.com
Subject: Re: [PATCH 0/5] prctl: extend PR_SET_THP_DISABLE to only provide
 THPs when advised

You forgot the v2, please can you resend this with it, or this will get
mighty confusing.

Thanks!

On Thu, Jul 31, 2025 at 01:18:11PM +0100, Usama Arif wrote:
> This will allow individual processes to opt-out of THP = "always"
> into THP = "madvise", without affecting other workloads on the system.
> This has been extensively discussed on the mailing list and has been
> summarized very well by David in the first patch which also includes
> the links to alternatives, please refer to the first patch commit message
> for the motivation for this series.
>
> Patch 1 adds the PR_THP_DISABLE_EXCEPT_ADVISED flag to implement this, along
> with the MMF changes.
> Patch 2 is a cleanup patch for tva_flags that will allow the forced collapse
> case to be transmitted to vma_thp_disabled (which is done in patch 3).
> Patches 4-5 implement the selftests for PR_SET_THP_DISABLE for completely
> disabling THPs (old behaviour) and only enabling it at advise
> (PR_THP_DISABLE_EXCEPT_ADVISED).
>
> The patches are tested on top of 4ad831303eca6ae518c3b3d86838a2a04b90ec41
> from mm-new.
>
> v1 -> v2: https://lore.kernel.org/all/20250725162258.1043176-1-usamaarif642@gmail.com/
> - Change thp_push_settings to thp_write_settings (David)
> - Add tests for all the system policies for the prctl call (David)
> - Small fixes and cleanups
>
> David Hildenbrand (3):
>   prctl: extend PR_SET_THP_DISABLE to optionally exclude VM_HUGEPAGE
>   mm/huge_memory: convert "tva_flags" to "enum tva_type" for
>     thp_vma_allowable_order*()
>   mm/huge_memory: treat MADV_COLLAPSE as an advise with
>     PR_THP_DISABLE_EXCEPT_ADVISED
>
> Usama Arif (2):
>   selftests: prctl: introduce tests for disabling THPs completely
>   selftests: prctl: introduce tests for disabling THPs except for
>     madvise
>
>  Documentation/filesystems/proc.rst            |   5 +-
>  fs/proc/array.c                               |   2 +-
>  fs/proc/task_mmu.c                            |   4 +-
>  include/linux/huge_mm.h                       |  60 ++-
>  include/linux/mm_types.h                      |  13 +-
>  include/uapi/linux/prctl.h                    |  10 +
>  kernel/sys.c                                  |  59 ++-
>  mm/huge_memory.c                              |  11 +-
>  mm/khugepaged.c                               |  20 +-
>  mm/memory.c                                   |  20 +-
>  mm/shmem.c                                    |   2 +-
>  tools/testing/selftests/mm/.gitignore         |   1 +
>  tools/testing/selftests/mm/Makefile           |   1 +
>  .../testing/selftests/mm/prctl_thp_disable.c  | 358 ++++++++++++++++++
>  tools/testing/selftests/mm/thp_settings.c     |   9 +-
>  tools/testing/selftests/mm/thp_settings.h     |   1 +
>  16 files changed, 505 insertions(+), 71 deletions(-)
>  create mode 100644 tools/testing/selftests/mm/prctl_thp_disable.c
>
> --
> 2.47.3
>