On 29 May 2025, at 4:23, Baolin Wang wrote:
> The MADV_COLLAPSE will ignore the system-wide Anon THP sysfs settings, which
> means that even though we have disabled the Anon THP configuration, MADV_COLLAPSE
> will still attempt to collapse into a Anon THP. This violates the rule we have
> agreed upon: never means never.
>
> To address this issue, should check whether the Anon THP configuration is disabled
> in thp_vma_allowable_orders(), even when the TVA_ENFORCE_SYSFS flag is set.
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
> include/linux/huge_mm.h | 23 +++++++++++++++++++----
> 1 file changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 2f190c90192d..199ddc9f04a1 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -287,20 +287,35 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
> unsigned long orders)
> {
> /* Optimization to check if required orders are enabled early. */
> - if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
> - unsigned long mask = READ_ONCE(huge_anon_orders_always);
> + if (vma_is_anonymous(vma)) {
> + unsigned long always = READ_ONCE(huge_anon_orders_always);
> + unsigned long madvise = READ_ONCE(huge_anon_orders_madvise);
> + unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);
> + unsigned long mask = always | madvise;
> +
> + /*
> + * If the system-wide THP/mTHP sysfs settings are disabled,
> + * then we should never allow hugepages.
> + */
> + if (!(mask & orders) && !(hugepage_global_enabled() && (inherit & orders)))
Can you explain the logic here? Is it equivalent to:
1. if THP is set to always, always_mask & orders == 0, or
2. if THP if set to madvise, madvise_mask & order == 0, or
3. if THP is set to inherit, inherit_mask & order == 0?
I cannot figure out why (always | madvise) & orders does not check
THP enablement case, but inherit & orders checks hugepage_global_enabled().
Thanks.
> + return 0;
> +
> + if (!(tva_flags & TVA_ENFORCE_SYSFS))
> + goto skip;
>
> + mask = always;
> if (vm_flags & VM_HUGEPAGE)
> - mask |= READ_ONCE(huge_anon_orders_madvise);
> + mask |= madvise;
> if (hugepage_global_always() ||
> ((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled()))
> - mask |= READ_ONCE(huge_anon_orders_inherit);
> + mask |= inherit;
>
> orders &= mask;
> if (!orders)
> return 0;
> }
>
> +skip:
> return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
> }
>
> --
> 2.43.5
Best Regards,
Yan, Zi
