Re: [RFC PATCH v3 3/4] mm: add do_set_pte_range()

[Chih-En Lin <shiyn.lin@gmail.com>]

On Fri, Feb 03, 2023 at 09:16:35PM +0800, 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@intel.com>
> ---
>  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);

Why don't use is_cow_mapping()?
Is there anything messed up with VM_MAYWRITE?

>  	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);

Here too.

> +
> +	if (cow) {
>  		inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
>  		page_add_new_anon_rmap(page, vma, addr);
>  		lru_cache_add_inactive_or_unevictable(page, vma);
> -	} else {
> -		inc_mm_counter(vma->vm_mm, mm_counter_file(page));
> -		page_add_file_rmap(page, vma, false);
>  	}
> -	set_pte_at(vma->vm_mm, addr, vmf->pte, entry);
> +
> +	do_set_pte_range(vmf, folio, addr, vmf->pte,
> +			folio_page_idx(folio, page), 1);
>  }
>  
>  static bool vmf_pte_changed(struct vm_fault *vmf)
> @@ -4361,9 +4383,6 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
>  	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);
> -
>  		ret = 0;
>  	} else {
>  		update_mmu_tlb(vma, vmf->address, vmf->pte);
> -- 
> 2.30.2
> 
> 

Thanks,
Chih-En Lin