On 03/17/2022 08:23 PM, Matthew Wilcox wrote:
> 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?
It is only performance issue, and there is no obvious performance
improvement for general workloads on my hand, but I do not test
it on microbenchmark.
>
>> 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
>>
>>
