On Wed, Sep 10, 2025 at 10:44:40AM +0800, Yafang Shao wrote:
> The new BPF capability enables finer-grained THP policy decisions by
> introducing separate handling for swap faults versus normal page faults.
>
> As highlighted by Barry:
>
> We’ve observed that swapping in large folios can lead to more
> swap thrashing for some workloads- e.g. kernel build. Consequently,
> some workloads might prefer swapping in smaller folios than those
> allocated by alloc_anon_folio().
>
> While prtcl() could potentially be extended to leverage this new policy,
> doing so would require modifications to the uAPI.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Other than nits, these seems fine, so:
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Cc: Barry Song <21cnbao@xxxxxxxxx>
> ---
> include/linux/huge_mm.h | 3 ++-
> mm/huge_memory.c | 2 +-
> mm/memory.c | 2 +-
> 3 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index f72a5fd04e4f..b9742453806f 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -97,9 +97,10 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
>
> enum tva_type {
> TVA_SMAPS, /* Exposing "THPeligible:" in smaps. */
> - TVA_PAGEFAULT, /* Serving a page fault. */
> + TVA_PAGEFAULT, /* Serving a non-swap page fault. */
> TVA_KHUGEPAGED, /* Khugepaged collapse. */
> TVA_FORCED_COLLAPSE, /* Forced collapse (e.g. MADV_COLLAPSE). */
> + TVA_SWAP, /* Serving a swap */
Serving a swap what? :) I think TVA_SWAP_PAGEFAULT would be better here right?
And 'serving a swap page fault'.
> };
>
> #define thp_vma_allowable_order(vma, vm_flags, type, order) \
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 26cedfcd7418..523153d21a41 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -103,7 +103,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
> unsigned long orders)
> {
> const bool smaps = type == TVA_SMAPS;
> - const bool in_pf = type == TVA_PAGEFAULT;
> + const bool in_pf = (type == TVA_PAGEFAULT || type == TVA_SWAP);
> const bool forced_collapse = type == TVA_FORCED_COLLAPSE;
> unsigned long supported_orders;
>
> diff --git a/mm/memory.c b/mm/memory.c
> index d9de6c056179..d8819cac7930 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4515,7 +4515,7 @@ 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_PAGEFAULT,
> + orders = thp_vma_allowable_orders(vma, vma->vm_flags, TVA_SWAP,
> BIT(PMD_ORDER) - 1);
> orders = thp_vma_suitable_orders(vma, vmf->address, orders);
> orders = thp_swap_suitable_orders(swp_offset(entry),
> --
> 2.47.3
>
