On Wed, Sep 10, 2025 at 11:00 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> Currently, THP allocation cannot be restricted to khugepaged alone while
> being disabled in the page fault path. This limitation exists because
> disabling THP allocation during page faults also prevents the execution of
> khugepaged_enter_vma() in that path.
>
> With the introduction of BPF, we can now implement THP policies based on
> different TVA types. This patch adjusts the logic to support this new
> capability.
>
> While we could also extend prtcl() to utilize this new policy, such a
> change would require a uAPI modification.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
> mm/huge_memory.c | 1 -
> mm/memory.c | 13 ++++++++-----
> 2 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 523153d21a41..1e9e7b32e2cf 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1346,7 +1346,6 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
> ret = vmf_anon_prepare(vmf);
> if (ret)
> return ret;
> - khugepaged_enter_vma(vma, vma->vm_flags);
>
> if (!(vmf->flags & FAULT_FLAG_WRITE) &&
> !mm_forbids_zeropage(vma->vm_mm) &&
> diff --git a/mm/memory.c b/mm/memory.c
> index d8819cac7930..d0609dc1e371 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6289,11 +6289,14 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
> if (pud_trans_unstable(vmf.pud))
> goto retry_pud;
>
> - if (pmd_none(*vmf.pmd) &&
> - thp_vma_allowable_order(vma, vm_flags, TVA_PAGEFAULT, PMD_ORDER)) {
> - ret = create_huge_pmd(&vmf);
> - if (!(ret & VM_FAULT_FALLBACK))
> - return ret;
> + if (pmd_none(*vmf.pmd)) {
> + if (vma_is_anonymous(vma))
> + khugepaged_enter_vma(vma, vm_flags);
Hmm... I'm a bit confused about the different conditions for calling
khugepaged_enter_vma(). It's sometimes called for anonymous VMAs, other
times ONLY for non-anonymous, and sometimes unconditionally ;)
Anyway, this isn't a blocker, just something I noticed. I might try to
simplify that down the road.
Acked-by: Lance Yang <lance.yang@xxxxxxxxx>
Cheers,
Lance
> + if (thp_vma_allowable_order(vma, vm_flags, TVA_PAGEFAULT, PMD_ORDER)) {
> + ret = create_huge_pmd(&vmf);
> + if (!(ret & VM_FAULT_FALLBACK))
> + return ret;
> + }
> } else {
> vmf.orig_pmd = pmdp_get_lockless(vmf.pmd);
>
> --
> 2.47.3
>
>
