Re: [PATCH v4 35/36] mm: Convert do_set_pte() to set_pte_range()

From: Yin, Fengwei
Date: Thu Mar 16 2023 - 12:26:18 EST



On 3/15/2023 11:26 PM, Ryan Roberts wrote:
> On 15/03/2023 05:14, Matthew Wilcox (Oracle) wrote:
>> From: Yin Fengwei <fengwei.yin@xxxxxxxxx>
>>
>> set_pte_range() allows to setup page table entries for a specific
>> range. It takes advantage of batched rmap update for large folio.
>> It now takes care of calling update_mmu_cache_range().
>>
>> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
>> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
>> ---
>> Documentation/filesystems/locking.rst | 2 +-
>> include/linux/mm.h | 3 ++-
>> mm/filemap.c | 3 +--
>> mm/memory.c | 27 +++++++++++++++------------
>> 4 files changed, 19 insertions(+), 16 deletions(-)
>>
>> diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
>> index 7de7a7272a5e..922886fefb7f 100644
>> --- a/Documentation/filesystems/locking.rst
>> +++ b/Documentation/filesystems/locking.rst
>> @@ -663,7 +663,7 @@ locked. The VM will unlock the page.
>> Filesystem should find and map pages associated with offsets from "start_pgoff"
>> till "end_pgoff". ->map_pages() is called with page table locked and must
>> not block. If it's not possible to reach a page without blocking,
>> -filesystem should skip it. Filesystem should use do_set_pte() to setup
>> +filesystem should skip it. Filesystem should use set_pte_range() to setup
>> page table entry. Pointer to entry associated with the page is passed in
>> "pte" field in vm_fault structure. Pointers to entries for other offsets
>> should be calculated relative to "pte".
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index ee755bb4e1c1..81788c985a8c 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1299,7 +1299,8 @@ 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 set_pte_range(struct vm_fault *vmf, struct folio *folio,
>> + struct page *page, unsigned int nr, unsigned long addr);
>>
>> 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 6e2b0778db45..e2317623dcbf 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -3504,8 +3504,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>> ret = VM_FAULT_NOPAGE;
>>
>> ref_count++;
>> - do_set_pte(vmf, page, addr);
>> - update_mmu_cache(vma, addr, vmf->pte);
>> + set_pte_range(vmf, folio, page, 1, addr);
>> } 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 6aa21e8f3753..9a654802f104 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4274,7 +4274,8 @@ 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 set_pte_range(struct vm_fault *vmf, struct folio *folio,
>> + struct page *page, unsigned int nr, unsigned long addr)
>> {
>> struct vm_area_struct *vma = vmf->vma;
>> bool uffd_wp = vmf_orig_pte_uffd_wp(vmf);
>> @@ -4282,7 +4283,7 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
>> bool prefault = vmf->address != addr;
>
> I think you are changing behavior here - is this intentional? Previously this
> would be evaluated per page, now its evaluated once for the whole range. The
> intention below is that directly faulted pages are mapped young and prefaulted
> pages are mapped old. But now a whole range will be mapped the same.

Yes. You are right here.

Look at the prefault and cpu_has_hw_af for ARM64, it looks like we
can avoid to handle vmf->address == addr specially. It's OK to
drop prefault and change the logic here a little bit to:
if (arch_wants_old_prefaulted_pte())
entry = pte_mkold(entry);
else
entry = pte_sw_mkyong(entry);

It's not necessary to use pte_sw_mkyong for vmf->address == addr
because HW will set the ACCESS bit in page table entry.

Add Will Deacon in case I missed something here. Thanks.


Regards
Yin, Fengwei

>
> Thanks,
> Ryan
>
>> pte_t entry;
>>
>> - flush_icache_page(vma, page);
>> + flush_icache_pages(vma, page, nr);
>> entry = mk_pte(page, vma->vm_page_prot);
>>
>> if (prefault && arch_wants_old_prefaulted_pte())
>> @@ -4296,14 +4297,18 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
>> entry = pte_mkuffd_wp(entry);
>> /* copy-on-write page */
>> if (write && !(vma->vm_flags & VM_SHARED)) {
>> - inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
>> - page_add_new_anon_rmap(page, vma, addr);
>> - lru_cache_add_inactive_or_unevictable(page, vma);
>> + add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr);
>> + VM_BUG_ON_FOLIO(nr != 1, folio);
>> + folio_add_new_anon_rmap(folio, vma, addr);
>> + folio_add_lru_vma(folio, vma);
>> } else {
>> - inc_mm_counter(vma->vm_mm, mm_counter_file(page));
>> - page_add_file_rmap(page, vma, false);
>> + add_mm_counter(vma->vm_mm, mm_counter_file(page), nr);
>> + folio_add_file_rmap_range(folio, page, nr, vma, false);
>> }
>> - set_pte_at(vma->vm_mm, addr, vmf->pte, entry);
>> + set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr);
>> +
>> + /* no need to invalidate: a not-present page won't be cached */
>> + update_mmu_cache_range(vma, addr, vmf->pte, nr);
>> }
>>
>> static bool vmf_pte_changed(struct vm_fault *vmf)
>> @@ -4376,11 +4381,9 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
>>
>> /* Re-check under ptl */
>> if (likely(!vmf_pte_changed(vmf))) {
>> - do_set_pte(vmf, page, vmf->address);
>> -
>> - /* no need to invalidate: a not-present page won't be cached */
>> - update_mmu_cache(vma, vmf->address, vmf->pte);
>> + struct folio *folio = page_folio(page);
>>
>> + set_pte_range(vmf, folio, page, 1, vmf->address);
>> ret = 0;
>> } else {
>> update_mmu_tlb(vma, vmf->address, vmf->pte);
>