linux-kernel - Re: [PATCH 02/12] filemap: Use folio_put_refs() in filemap_free

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Date:   Mon, 17 Jan 2022 18:56:41 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 02/12] filemap: Use folio_put_refs() in
 filemap_free_folio()

On Sun, Jan 16, 2022 at 12:18:12PM +0000, Matthew Wilcox (Oracle) wrote:
> This shrinks filemap_free_folio() by 55 bytes in my .config; 24 bytes
> from removing the VM_BUG_ON_FOLIO() and 31 bytes from unifying the
> small/large folio paths.
> 
> We could just use folio_ref_sub() here since the caller should hold a
> reference (as the VM_BUG_ON_FOLIO() was asserting), but that's fragile.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  mm/filemap.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 2fd9b2f24025..afc8f5ca85ac 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -231,17 +231,15 @@ void __filemap_remove_folio(struct folio *folio, void *shadow)
>  void filemap_free_folio(struct address_space *mapping, struct folio *folio)
>  {
>  	void (*freepage)(struct page *);
> +	int refs = 1;
>  
>  	freepage = mapping->a_ops->freepage;
>  	if (freepage)
>  		freepage(&folio->page);
>  
> -	if (folio_test_large(folio) && !folio_test_hugetlb(folio)) {
> -		folio_ref_sub(folio, folio_nr_pages(folio));
> -		VM_BUG_ON_FOLIO(folio_ref_count(folio) <= 0, folio);
> -	} else {
> -		folio_put(folio);
> -	}
> +	if (folio_test_large(folio) && !folio_test_hugetlb(folio))
> +		refs = folio_nr_pages(folio);

Isn't folio_test_large() check redundant? folio_nr_pages() would return 1
for non-large folio, wouldn't it?

> +	folio_put_refs(folio, refs);
>  }
>  
>  /**
> -- 
> 2.34.1
> 

-- 
 Kirill A. Shutemov