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

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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);
> 



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