On 2/3/2023 9:34 PM, David Hildenbrand wrote:
> On 03.02.23 14:30, Yin, Fengwei wrote:
>>
>>
>> On 2/3/2023 9:25 PM, David Hildenbrand wrote:
>>> On 03.02.23 14:16, Yin Fengwei wrote:
>>>> do_set_pte_range() allows to setup page table entries for a
>>>> specific range. It calls folio_add_file_rmap_range() to take
>>>> advantage of batched rmap update for large folio.
>>>>
>>>> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
>>>> ---
>>>> include/linux/mm.h | 3 +++
>>>> mm/filemap.c | 1 -
>>>> mm/memory.c | 59 ++++++++++++++++++++++++++++++----------------
>>>> 3 files changed, 42 insertions(+), 21 deletions(-)
>>>>
>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>> index d6f8f41514cc..93192f04b276 100644
>>>> --- a/include/linux/mm.h
>>>> +++ b/include/linux/mm.h
>>>> @@ -1162,6 +1162,9 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
>>>> vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page);
>>>> void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr);
>>>> +void do_set_pte_range(struct vm_fault *vmf, struct folio *folio,
>>>> + unsigned long addr, pte_t *pte,
>>>> + unsigned long start, unsigned int nr);
>>>> vm_fault_t finish_fault(struct vm_fault *vmf);
>>>> vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
>>>> diff --git a/mm/filemap.c b/mm/filemap.c
>>>> index f444684db9f2..74046a3a0ff5 100644
>>>> --- a/mm/filemap.c
>>>> +++ b/mm/filemap.c
>>>> @@ -3386,7 +3386,6 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>>>> ref_count++;
>>>> do_set_pte(vmf, page, addr);
>>>> - update_mmu_cache(vma, addr, vmf->pte);
>>>> } while (vmf->pte++, page++, addr += PAGE_SIZE, ++count < nr_pages);
>>>> /* Restore the vmf->pte */
>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>> index 7a04a1130ec1..3754b2ef166a 100644
>>>> --- a/mm/memory.c
>>>> +++ b/mm/memory.c
>>>> @@ -4257,36 +4257,58 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>>>> }
>>>> #endif
>>>> -void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
>>>> +void do_set_pte_range(struct vm_fault *vmf, struct folio *folio,
>>>> + unsigned long addr, pte_t *pte,
>>>> + unsigned long start, unsigned int nr)
>>>> {
>>>> struct vm_area_struct *vma = vmf->vma;
>>>> bool uffd_wp = pte_marker_uffd_wp(vmf->orig_pte);
>>>> bool write = vmf->flags & FAULT_FLAG_WRITE;
>>>> + bool cow = write && !(vma->vm_flags & VM_SHARED);
>>>> bool prefault = vmf->address != addr;
>>>> + struct page *page = folio_page(folio, start);
>>>> pte_t entry;
>>>> - flush_icache_page(vma, page);
>>>> - entry = mk_pte(page, vma->vm_page_prot);
>>>> + if (!cow) {
>>>> + folio_add_file_rmap_range(folio, start, nr, vma, false);
>>>> + add_mm_counter(vma->vm_mm, mm_counter_file(page), nr);
>>>> + }
>>>> - if (prefault && arch_wants_old_prefaulted_pte())
>>>> - entry = pte_mkold(entry);
>>>> - else
>>>> - entry = pte_sw_mkyoung(entry);
>>>> + do {
>>>> + flush_icache_page(vma, page);
>>>> + entry = mk_pte(page, vma->vm_page_prot);
>>>> - if (write)
>>>> - entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>>>> - if (unlikely(uffd_wp))
>>>> - entry = pte_mkuffd_wp(entry);
>>>> - /* copy-on-write page */
>>>> - if (write && !(vma->vm_flags & VM_SHARED)) {
>>>> + if (prefault && arch_wants_old_prefaulted_pte())
>>>> + entry = pte_mkold(entry);
>>>> + else
>>>> + entry = pte_sw_mkyoung(entry);
>>>> +
>>>> + if (write)
>>>> + entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>>>> + if (unlikely(uffd_wp))
>>>> + entry = pte_mkuffd_wp(entry);
>>>> + set_pte_at(vma->vm_mm, addr, pte, entry);
>>>> +
>>>> + /* no need to invalidate: a not-present page won't be cached */
>>>> + update_mmu_cache(vma, addr, pte);
>>>> + } while (pte++, page++, addr += PAGE_SIZE, --nr > 0);
>>>> +}
>>>> +
>>>> +void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
>>>> +{
>>>> + struct folio *folio = page_folio(page);
>>>> + struct vm_area_struct *vma = vmf->vma;
>>>> + bool cow = (vmf->flags & FAULT_FLAG_WRITE) &&
>>>> + !(vma->vm_flags & VM_SHARED);
>>>> +
>>>> + if (cow) {
>>>> inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
>>>> page_add_new_anon_rmap(page, vma, addr);
>>>
>>> As raised, we cannot PTE-map a multi-page folio that way.
>>>
>>> This function only supports single-page anon folios.
>>>
>>> page_add_new_anon_rmap() -> folio_add_new_anon_rmap(). As that documents:
>>>
>>> "If the folio is large, it is accounted as a THP" -- for example, we would only increment the "entire mapcount" and set the PageAnonExclusive bit only on the head page.
>>>
>>> So this really doesn't work for multi-page folios and if the function would be used for that, we'd be in trouble.
>>>
>>> We'd want some fence here to detect that and bail out if we'd be instructed to do that. At least a WARN_ON_ONCE() I guess.
>>> update_mmu_tlb(vma, vmf->address, vmf->pte);
>>>
>>> Right now the function looks like it might just handle that.
>> You are right. I thought moving cow case out of it can make it explicit.
>> But looks like it doesn't. I will add WARN_ON_ONCE(). Thanks.
>
> I guess I would move the cow check into do_set_pte_range() as well, and verify in there that we are really only dealing with a single-page folio, commenting that rmap code would need serious adjustment to make it work and that current code never passes a multi-page folio.
Yes. There is !cow in do_set_pte_range() already. I planned to add
WARN_ON_ONCE() on else case there. Thanks.
Regards
Yin, Fengwei
>
> Thanks!
>
