Re: [RFC PATCH v3 1/4] filemap: add function filemap_map_folio_range()

["Yin, Fengwei" <fengwei.yin@intel.com>]

On 2/3/2023 10:17 PM, Kirill A. Shutemov wrote:
> On Fri, Feb 03, 2023 at 09:16:33PM +0800, Yin Fengwei wrote:
>> @@ -3378,45 +3425,18 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
>>  	addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
>>  	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
>>  	do {
>> -again:
>> -		page = folio_file_page(folio, xas.xa_index);
>> -		if (PageHWPoison(page))
>> -			goto unlock;
>> -
>> -		if (mmap_miss > 0)
>> -			mmap_miss--;
>> +		unsigned long end;
>>  
>>  		addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
>>  		vmf->pte += xas.xa_index - last_pgoff;
>>  		last_pgoff = xas.xa_index;
>> +		end = folio->index + folio_nr_pages(folio) - 1;
>> +		nr_pages = min(end, end_pgoff) - xas.xa_index + 1;
>>  
>> -		/*
>> -		 * NOTE: If there're PTE markers, we'll leave them to be
>> -		 * handled in the specific fault path, and it'll prohibit the
>> -		 * fault-around logic.
>> -		 */
>> -		if (!pte_none(*vmf->pte))
>> -			goto unlock;
>> -
>> -		/* We're about to handle the fault */
>> -		if (vmf->address == addr)
>> -			ret = VM_FAULT_NOPAGE;
>> +		ret |=	filemap_map_folio_range(vmf, folio,
>> +				xas.xa_index - folio->index, addr, nr_pages);
>> +		xas.xa_index = end;
> 
> IIRC, end here can be beyond end_pgoff. Can it cause an issue? I don't see
> it, but just in case.
Yes. end can beyond end_pgoff. And it's fine because that will end the loop
and no access to xas.xa_index after that. But let me change the line to:
   xas.xa_index += nr_pages;
to keep the same behavior as before in next version. Thanks.

Regards
Yin, Fengwei

> 
>