Re: [PATCH v4 2/7] mm/huge_memory: convert "tva_flags" to "enum tva_type"

[Yafang Shao <laoar.shao@gmail.com>]

On Wed, Aug 13, 2025 at 9:57 PM Usama Arif <usamaarif642@gmail.com> wrote:
>
> From: David Hildenbrand <david@redhat.com>
>
> When determining which THP orders are eligible for a VMA mapping,
> we have previously specified tva_flags, however it turns out it is
> really not necessary to treat these as flags.
>
> Rather, we distinguish between distinct modes.
>
> The only case where we previously combined flags was with
> TVA_ENFORCE_SYSFS, but we can avoid this by observing that this
> is the default, except for MADV_COLLAPSE or an edge cases in
> collapse_pte_mapped_thp() and hugepage_vma_revalidate(), and
> adding a mode specifically for this case - TVA_FORCED_COLLAPSE.
>
> We have:
> * smaps handling for showing "THPeligible"
> * Pagefault handling
> * khugepaged handling
> * Forced collapse handling: primarily MADV_COLLAPSE, but also for
>   an edge case in collapse_pte_mapped_thp()
>
> Disregarding the edge cases, we only want to ignore sysfs settings only
> when we are forcing a collapse through MADV_COLLAPSE, otherwise we
> want to enforce it, hence this patch does the following flag to enum
> conversions:
>
> * TVA_SMAPS | TVA_ENFORCE_SYSFS -> TVA_SMAPS
> * TVA_IN_PF | TVA_ENFORCE_SYSFS -> TVA_PAGEFAULT
> * TVA_ENFORCE_SYSFS             -> TVA_KHUGEPAGED
> * 0                             -> TVA_FORCED_COLLAPSE
>
> With this change, we immediately know if we are in the forced collapse
> case, which will be valuable next.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> Acked-by: Usama Arif <usamaarif642@gmail.com>
> Signed-off-by: Usama Arif <usamaarif642@gmail.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Acked-by: Yafang Shao <laoar.shao@gmail.com>

Hello Usama,

This change is also required by my BPF-based THP order selection
series [0]. Since this patch appears to be independent of the series,
could we merge it first into mm-new or mm-everything if the series
itself won't be merged shortly?

Link: https://lwn.net/Articles/1031829/ [0]

> ---
>  fs/proc/task_mmu.c      |  4 ++--
>  include/linux/huge_mm.h | 30 ++++++++++++++++++------------
>  mm/huge_memory.c        |  8 ++++----
>  mm/khugepaged.c         | 17 ++++++++---------
>  mm/memory.c             | 14 ++++++--------
>  5 files changed, 38 insertions(+), 35 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index e8e7bef345313..ced01cf3c5ab3 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1369,8 +1369,8 @@ static int show_smap(struct seq_file *m, void *v)
>         __show_smap(m, &mss, false);
>
>         seq_printf(m, "THPeligible:    %8u\n",
> -                  !!thp_vma_allowable_orders(vma, vma->vm_flags,
> -                          TVA_SMAPS | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL));
> +                  !!thp_vma_allowable_orders(vma, vma->vm_flags, TVA_SMAPS,
> +                                             THP_ORDERS_ALL));
>
>         if (arch_pkeys_enabled())
>                 seq_printf(m, "ProtectionKey:  %8u\n", vma_pkey(vma));
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 22b8b067b295e..92ea0b9771fae 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -94,12 +94,15 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
>  #define THP_ORDERS_ALL \
>         (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_SPECIAL | THP_ORDERS_ALL_FILE_DEFAULT)
>
> -#define TVA_SMAPS              (1 << 0)        /* Will be used for procfs */
> -#define TVA_IN_PF              (1 << 1)        /* Page fault handler */
> -#define TVA_ENFORCE_SYSFS      (1 << 2)        /* Obey sysfs configuration */
> +enum tva_type {
> +       TVA_SMAPS,              /* Exposing "THPeligible:" in smaps. */
> +       TVA_PAGEFAULT,          /* Serving a page fault. */
> +       TVA_KHUGEPAGED,         /* Khugepaged collapse. */
> +       TVA_FORCED_COLLAPSE,    /* Forced collapse (e.g. MADV_COLLAPSE). */
> +};
>
> -#define thp_vma_allowable_order(vma, vm_flags, tva_flags, order) \
> -       (!!thp_vma_allowable_orders(vma, vm_flags, tva_flags, BIT(order)))
> +#define thp_vma_allowable_order(vma, vm_flags, type, order) \
> +       (!!thp_vma_allowable_orders(vma, vm_flags, type, BIT(order)))
>
>  #define split_folio(f) split_folio_to_list(f, NULL)
>
> @@ -264,14 +267,14 @@ static inline unsigned long thp_vma_suitable_orders(struct vm_area_struct *vma,
>
>  unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
>                                          vm_flags_t vm_flags,
> -                                        unsigned long tva_flags,
> +                                        enum tva_type type,
>                                          unsigned long orders);
>
>  /**
>   * thp_vma_allowable_orders - determine hugepage orders that are allowed for vma
>   * @vma:  the vm area to check
>   * @vm_flags: use these vm_flags instead of vma->vm_flags
> - * @tva_flags: Which TVA flags to honour
> + * @type: TVA type
>   * @orders: bitfield of all orders to consider
>   *
>   * Calculates the intersection of the requested hugepage orders and the allowed
> @@ -285,11 +288,14 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
>  static inline
>  unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>                                        vm_flags_t vm_flags,
> -                                      unsigned long tva_flags,
> +                                      enum tva_type type,
>                                        unsigned long orders)
>  {
> -       /* Optimization to check if required orders are enabled early. */
> -       if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
> +       /*
> +        * Optimization to check if required orders are enabled early. Only
> +        * forced collapse ignores sysfs configs.
> +        */
> +       if (type != TVA_FORCED_COLLAPSE && vma_is_anonymous(vma)) {
>                 unsigned long mask = READ_ONCE(huge_anon_orders_always);
>
>                 if (vm_flags & VM_HUGEPAGE)
> @@ -303,7 +309,7 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>                         return 0;
>         }
>
> -       return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
> +       return __thp_vma_allowable_orders(vma, vm_flags, type, orders);
>  }
>
>  struct thpsize {
> @@ -547,7 +553,7 @@ static inline unsigned long thp_vma_suitable_orders(struct vm_area_struct *vma,
>
>  static inline unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>                                         vm_flags_t vm_flags,
> -                                       unsigned long tva_flags,
> +                                       enum tva_type type,
>                                         unsigned long orders)
>  {
>         return 0;
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 6df1ed0cef5cf..9c716be949cbf 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -99,12 +99,12 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
>
>  unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
>                                          vm_flags_t vm_flags,
> -                                        unsigned long tva_flags,
> +                                        enum tva_type type,
>                                          unsigned long orders)
>  {
> -       bool smaps = tva_flags & TVA_SMAPS;
> -       bool in_pf = tva_flags & TVA_IN_PF;
> -       bool enforce_sysfs = tva_flags & TVA_ENFORCE_SYSFS;
> +       const bool smaps = type == TVA_SMAPS;
> +       const bool in_pf = type == TVA_PAGEFAULT;
> +       const bool enforce_sysfs = type != TVA_FORCED_COLLAPSE;
>         unsigned long supported_orders;
>
>         /* Check the intersection of requested and supported orders. */
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 1a416b8659972..d3d4f116e14b6 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -474,8 +474,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
>  {
>         if (!mm_flags_test(MMF_VM_HUGEPAGE, vma->vm_mm) &&
>             hugepage_pmd_enabled()) {
> -               if (thp_vma_allowable_order(vma, vm_flags, TVA_ENFORCE_SYSFS,
> -                                           PMD_ORDER))
> +               if (thp_vma_allowable_order(vma, vm_flags, TVA_KHUGEPAGED, PMD_ORDER))
>                         __khugepaged_enter(vma->vm_mm);
>         }
>  }
> @@ -921,7 +920,8 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
>                                    struct collapse_control *cc)
>  {
>         struct vm_area_struct *vma;
> -       unsigned long tva_flags = cc->is_khugepaged ? TVA_ENFORCE_SYSFS : 0;
> +       enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED :
> +                                TVA_FORCED_COLLAPSE;
>
>         if (unlikely(hpage_collapse_test_exit_or_disable(mm)))
>                 return SCAN_ANY_PROCESS;
> @@ -932,7 +932,7 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
>
>         if (!thp_vma_suitable_order(vma, address, PMD_ORDER))
>                 return SCAN_ADDRESS_RANGE;
> -       if (!thp_vma_allowable_order(vma, vma->vm_flags, tva_flags, PMD_ORDER))
> +       if (!thp_vma_allowable_order(vma, vma->vm_flags, type, PMD_ORDER))
>                 return SCAN_VMA_CHECK;
>         /*
>          * Anon VMA expected, the address may be unmapped then
> @@ -1533,9 +1533,9 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
>          * in the page cache with a single hugepage. If a mm were to fault-in
>          * this memory (mapped by a suitably aligned VMA), we'd get the hugepage
>          * and map it by a PMD, regardless of sysfs THP settings. As such, let's
> -        * analogously elide sysfs THP settings here.
> +        * analogously elide sysfs THP settings here and force collapse.
>          */
> -       if (!thp_vma_allowable_order(vma, vma->vm_flags, 0, PMD_ORDER))
> +       if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER))
>                 return SCAN_VMA_CHECK;
>
>         /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
> @@ -2432,8 +2432,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
>                         progress++;
>                         break;
>                 }
> -               if (!thp_vma_allowable_order(vma, vma->vm_flags,
> -                                       TVA_ENFORCE_SYSFS, PMD_ORDER)) {
> +               if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
>  skip:
>                         progress++;
>                         continue;
> @@ -2767,7 +2766,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>         BUG_ON(vma->vm_start > start);
>         BUG_ON(vma->vm_end < end);
>
> -       if (!thp_vma_allowable_order(vma, vma->vm_flags, 0, PMD_ORDER))
> +       if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER))
>                 return -EINVAL;
>
>         cc = kmalloc(sizeof(*cc), GFP_KERNEL);
> diff --git a/mm/memory.c b/mm/memory.c
> index 002c28795d8b7..7b1e8f137fa3f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4515,8 +4515,8 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
>          * Get a list of all the (large) orders below PMD_ORDER that are enabled
>          * and suitable for swapping THP.
>          */
> -       orders = thp_vma_allowable_orders(vma, vma->vm_flags,
> -                       TVA_IN_PF | TVA_ENFORCE_SYSFS, BIT(PMD_ORDER) - 1);
> +       orders = thp_vma_allowable_orders(vma, vma->vm_flags, TVA_PAGEFAULT,
> +                                         BIT(PMD_ORDER) - 1);
>         orders = thp_vma_suitable_orders(vma, vmf->address, orders);
>         orders = thp_swap_suitable_orders(swp_offset(entry),
>                                           vmf->address, orders);
> @@ -5063,8 +5063,8 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
>          * for this vma. Then filter out the orders that can't be allocated over
>          * the faulting address and still be fully contained in the vma.
>          */
> -       orders = thp_vma_allowable_orders(vma, vma->vm_flags,
> -                       TVA_IN_PF | TVA_ENFORCE_SYSFS, BIT(PMD_ORDER) - 1);
> +       orders = thp_vma_allowable_orders(vma, vma->vm_flags, TVA_PAGEFAULT,
> +                                         BIT(PMD_ORDER) - 1);
>         orders = thp_vma_suitable_orders(vma, vmf->address, orders);
>
>         if (!orders)
> @@ -6254,8 +6254,7 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
>                 return VM_FAULT_OOM;
>  retry_pud:
>         if (pud_none(*vmf.pud) &&
> -           thp_vma_allowable_order(vma, vm_flags,
> -                               TVA_IN_PF | TVA_ENFORCE_SYSFS, PUD_ORDER)) {
> +           thp_vma_allowable_order(vma, vm_flags, TVA_PAGEFAULT, PUD_ORDER)) {
>                 ret = create_huge_pud(&vmf);
>                 if (!(ret & VM_FAULT_FALLBACK))
>                         return ret;
> @@ -6289,8 +6288,7 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
>                 goto retry_pud;
>
>         if (pmd_none(*vmf.pmd) &&
> -           thp_vma_allowable_order(vma, vm_flags,
> -                               TVA_IN_PF | TVA_ENFORCE_SYSFS, PMD_ORDER)) {
> +           thp_vma_allowable_order(vma, vm_flags, TVA_PAGEFAULT, PMD_ORDER)) {
>                 ret = create_huge_pmd(&vmf);
>                 if (!(ret & VM_FAULT_FALLBACK))
>                         return ret;
> --
> 2.47.3
>


-- 
Regards
Yafang