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Message-ID: <97FEC8A9-A8F6-4023-913F-5187062B0E3A@nvidia.com>
Date: Wed, 07 May 2025 16:14:05 -0400
From: Zi Yan <ziy@...dia.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
linux-mm@...ck.org, hannes@...xchg.org, shakeel.butt@...ux.dev,
riel@...riel.com, baolin.wang@...ux.alibaba.com, lorenzo.stoakes@...cle.com,
Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 1/1] prctl: allow overriding system THP policy to always
per process
On 7 May 2025, at 10:00, Usama Arif wrote:
> Allowing override of global THP policy per process allows workloads
> that have shown to benefit from hugepages to do so, without regressing
> workloads that wouldn't benefit. This will allow such types of workloads
> to be run/stacked on the same machine.
>
> It also helps in rolling out hugepages in hyperscaler configurations
> for workloads that benefit from them, where a single THP policy is likely
> to be used across the entire fleet, and prctl will help override it.
>
> Signed-off-by: Usama Arif <usamaarif642@...il.com>
> ---
> include/linux/huge_mm.h | 3 ++-
> include/linux/mm_types.h | 7 ++-----
> include/uapi/linux/prctl.h | 3 +++
> kernel/sys.c | 16 ++++++++++++++++
> tools/include/uapi/linux/prctl.h | 3 +++
> .../perf/trace/beauty/include/uapi/linux/prctl.h | 3 +++
> 6 files changed, 29 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 2f190c90192d..0587dc4b8e2d 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -293,7 +293,8 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
> if (vm_flags & VM_HUGEPAGE)
> mask |= READ_ONCE(huge_anon_orders_madvise);
> if (hugepage_global_always() ||
> - ((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled()))
> + ((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled()) ||
> + test_bit(MMF_THP_ALWAYS, &vma->vm_mm->flags))
> mask |= READ_ONCE(huge_anon_orders_inherit);
>
> orders &= mask;
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index e76bade9ebb1..9bcd72b2b191 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1704,11 +1704,8 @@ enum {
> #define MMF_VM_MERGEABLE 16 /* KSM may merge identical pages */
> #define MMF_VM_HUGEPAGE 17 /* set when mm is available for khugepaged */
>
> -/*
> - * This one-shot flag is dropped due to necessity of changing exe once again
> - * on NFS restore
> - */
> -//#define MMF_EXE_FILE_CHANGED 18 /* see prctl_set_mm_exe_file() */
> +/* override inherited page sizes to always for the entire process */
> + #define MMF_THP_ALWAYS 18
Could we have something like MMF_THP_POLICY_SET and another field
for "always"? Otherwise, how are we going to set MMF_THP_MADVISE if
we want it in the future?
>
> #define MMF_HAS_UPROBES 19 /* has uprobes */
> #define MMF_RECALC_UPROBES 20 /* MMF_HAS_UPROBES can be wrong */
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 15c18ef4eb11..22c526681562 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -364,4 +364,7 @@ struct prctl_mm_map {
> # define PR_TIMER_CREATE_RESTORE_IDS_ON 1
> # define PR_TIMER_CREATE_RESTORE_IDS_GET 2
>
> +#define PR_SET_THP_ALWAYS 78
> +#define PR_GET_THP_ALWAYS 79
> +
> #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index c434968e9f5d..ee56b059ff1f 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2658,6 +2658,22 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> clear_bit(MMF_DISABLE_THP, &me->mm->flags);
> mmap_write_unlock(me->mm);
> break;
> + case PR_GET_THP_ALWAYS:
> + if (arg2 || arg3 || arg4 || arg5)
> + return -EINVAL;
> + error = !!test_bit(MMF_THP_ALWAYS, &me->mm->flags);
> + break;
> + case PR_SET_THP_ALWAYS:
> + if (arg3 || arg4 || arg5)
> + return -EINVAL;
> + if (mmap_write_lock_killable(me->mm))
> + return -EINTR;
> + if (arg2)
> + set_bit(MMF_THP_ALWAYS, &me->mm->flags);
> + else
> + clear_bit(MMF_THP_ALWAYS, &me->mm->flags);
> + mmap_write_unlock(me->mm);
> + break;
prctl can take more than one arguments. Would it be better to add
PR_SET_THP_POLICY and PR_GET_THP_POLICY and specify PR_THP_POLICY_ALWAYS
in the second argument? So that in the future, if we want to add
more THP policies, we do not need to keep piling up PR_{GET,SET}_THP_*?
> case PR_MPX_ENABLE_MANAGEMENT:
> case PR_MPX_DISABLE_MANAGEMENT:
> /* No longer implemented: */
> diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h
> index 35791791a879..f5f6cff42b3f 100644
> --- a/tools/include/uapi/linux/prctl.h
> +++ b/tools/include/uapi/linux/prctl.h
> @@ -328,4 +328,7 @@ struct prctl_mm_map {
> # define PR_PPC_DEXCR_CTRL_CLEAR_ONEXEC 0x10 /* Clear the aspect on exec */
> # define PR_PPC_DEXCR_CTRL_MASK 0x1f
>
> +#define PR_GET_THP_ALWAYS 78
> +#define PR_SET_THP_ALWAYS 79
> +
> #endif /* _LINUX_PRCTL_H */
> diff --git a/tools/perf/trace/beauty/include/uapi/linux/prctl.h b/tools/perf/trace/beauty/include/uapi/linux/prctl.h
> index 15c18ef4eb11..680996d56faf 100644
> --- a/tools/perf/trace/beauty/include/uapi/linux/prctl.h
> +++ b/tools/perf/trace/beauty/include/uapi/linux/prctl.h
> @@ -364,4 +364,7 @@ struct prctl_mm_map {
> # define PR_TIMER_CREATE_RESTORE_IDS_ON 1
> # define PR_TIMER_CREATE_RESTORE_IDS_GET 2
>
> +#define PR_GET_THP_ALWAYS 78
> +#define PR_SET_THP_ALWAYS 79
> +
> #endif /* _LINUX_PRCTL_H */
> --
> 2.47.1
--
Best Regards,
Yan, Zi
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