On Thu, Mar 17, 2022 at 02:50:33AM -0400, Bibo Mao wrote:
> On platforms like x86/arm which supports hw page walking, access
> and dirty bit is set by hw, however on some platforms without
> such hw functions, access and dirty bit is set by software in
> next trap.
>
> During numa page fault, dirty bit can be added for old pte if
> fail to migrate on write fault. And if it succeeds to migrate,
> access bit can be added for migrated new pte, also dirty bit
> can be added for write fault.
Is this a correctness problem, in which case this will need to be
backported, or is this a performance problem, in which case can you
share some numbers?
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
> mm/memory.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index c125c4969913..65813bec9c06 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4404,6 +4404,22 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
> if (migrate_misplaced_page(page, vma, target_nid)) {
> page_nid = target_nid;
> flags |= TNF_MIGRATED;
> +
> + /*
> + * update pte entry with access bit, and dirty bit for
> + * write fault
> + */
> + spin_lock(vmf->ptl);
> + pte = *vmf->pte;
> + pte = pte_mkyoung(pte);
> + if (was_writable) {
> + pte = pte_mkwrite(pte);
> + if (vmf->flags & FAULT_FLAG_WRITE)
> + pte = pte_mkdirty(pte);
> + }
> + set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
> + update_mmu_cache(vma, vmf->address, vmf->pte);
> + pte_unmap_unlock(vmf->pte, vmf->ptl);
> } else {
> flags |= TNF_MIGRATE_FAIL;
> vmf->pte = pte_offset_map(vmf->pmd, vmf->address);
> @@ -4427,8 +4443,11 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
> old_pte = ptep_modify_prot_start(vma, vmf->address, vmf->pte);
> pte = pte_modify(old_pte, vma->vm_page_prot);
> pte = pte_mkyoung(pte);
> - if (was_writable)
> + if (was_writable) {
> pte = pte_mkwrite(pte);
> + if (vmf->flags & FAULT_FLAG_WRITE)
> + pte = pte_mkdirty(pte);
> + }
> ptep_modify_prot_commit(vma, vmf->address, vmf->pte, old_pte, pte);
> update_mmu_cache(vma, vmf->address, vmf->pte);
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> --
> 2.31.1
>
>
