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

[Yin, Fengwei]

On 3/20/2023 10:08 PM, Matthew Wilcox wrote:
> On Mon, Mar 20, 2023 at 09:38:55PM +0800, Yin, Fengwei wrote:
>> Thanks a lot to Ryan for helping to test the debug patch I made.
>>
>> Ryan confirmed that the following change could fix the kernel build regression:
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index db86e459dde6..343d6ff36b2c 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -3557,7 +3557,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
>>
>>                 ret |= filemap_map_folio_range(vmf, folio,
>>                                 xas.xa_index - folio->index, addr, nr_pages);
>> -               xas.xa_index += nr_pages;
>> +               xas.xa_index += folio_test_large(folio) ? nr_pages : 0;
>>
>>                 folio_unlock(folio);
>>                 folio_put(folio);
>>
>> I will make upstream-able change as "xas.xa_index += nr_pages - 1;"
> 
> Thanks to both of you!
> 
> Really, we shouldn't need to interfere with xas.xa_index at all.
> Does this work?
I will give this a try and let you know the result.

> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 8e4f95c5b65a..e40c967dde5f 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3420,10 +3420,10 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
>  	return false;
>  }
>  
> -static struct folio *next_uptodate_page(struct folio *folio,
> -				       struct address_space *mapping,
> -				       struct xa_state *xas, pgoff_t end_pgoff)
> +static struct folio *next_uptodate_folio(struct xa_state *xas,
> +		struct address_space *mapping, pgoff_t end_pgoff)
>  {
> +	struct folio *folio = xas_next_entry(xas, end_pgoff);
>  	unsigned long max_idx;
>  
>  	do {
> @@ -3461,22 +3461,6 @@ static struct folio *next_uptodate_page(struct folio *folio,
>  	return NULL;
>  }
>  
> -static inline struct folio *first_map_page(struct address_space *mapping,
> -					  struct xa_state *xas,
> -					  pgoff_t end_pgoff)
> -{
> -	return next_uptodate_page(xas_find(xas, end_pgoff),
> -				  mapping, xas, end_pgoff);
> -}
> -
> -static inline struct folio *next_map_page(struct address_space *mapping,
> -					 struct xa_state *xas,
> -					 pgoff_t end_pgoff)
> -{
> -	return next_uptodate_page(xas_next_entry(xas, end_pgoff),
> -				  mapping, xas, end_pgoff);
> -}
> -
>  /*
>   * Map page range [start_page, start_page + nr_pages) of folio.
>   * start_page is gotten from start by folio_page(folio, start)
> @@ -3552,7 +3536,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
>  	int nr_pages = 0;
>  
>  	rcu_read_lock();
> -	folio = first_map_page(mapping, &xas, end_pgoff);
> +	folio = next_uptodate_folio(&xas, mapping, end_pgoff);
>  	if (!folio)
>  		goto out;
>  
> @@ -3574,11 +3558,11 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
>  
>  		ret |= filemap_map_folio_range(vmf, folio,
>  				xas.xa_index - folio->index, addr, nr_pages);
> -		xas.xa_index += nr_pages;
>  
>  		folio_unlock(folio);
>  		folio_put(folio);
> -	} while ((folio = next_map_page(mapping, &xas, end_pgoff)) != NULL);
> +		folio = next_uptodate_folio(&xas, mapping, end_pgoff);
> +	} while (folio);
>  	pte_unmap_unlock(vmf->pte, vmf->ptl);
>  out:
>  	rcu_read_unlock();
> 
>> Ryan and I also identify some other changes needed. I am not sure how to
>> integrate those changes to this series. Maybe an add-on patch after this
>> series? Thanks.
> 
> Up to you; I'm happy to integrate fixup patches into the current series
> or add on new ones.
Integrating to current series should be better. As it doesn't impact the
bisect operations. I will share the changes Ryan and I had after verify
the above change you proposed. Thanks.


Regards
Yin, Fengwei