linux-kernel - Re: [PATCH 70/71] mm: get rid of PAGE_CACHE_* and page_cache

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Date:	Sun, 20 Mar 2016 16:59:58 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 70/71] mm: get rid of PAGE_CACHE_* and
 page_cache_{get,release} macros

On Sun, Mar 20, 2016 at 09:41:17PM +0300, Kirill A. Shutemov wrote:
> PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time ago
> with promise that one day it will be possible to implement page cache with
> bigger chunks than PAGE_SIZE.
> 
> This promise never materialized. And unlikely will.
> 
> We have many places where PAGE_CACHE_SIZE assumed to be equal to
> PAGE_SIZE. And it's constant source of confusion on whether PAGE_CACHE_*
> or PAGE_* constant should be used in a particular case, especially on the
> border between fs and mm.
> 
> Global switching to PAGE_CACHE_SIZE != PAGE_SIZE would cause to much
> breakage to be doable.
> 
> Let's stop pretending that pages in page cache are special. They are not.
> 
> The changes are pretty straight-forward:
> 
>  - <foo> << (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;
> 
>  - PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} -> PAGE_{SIZE,SHIFT,MASK,ALIGN};
> 
>  - page_cache_get() -> get_page();
> 
>  - page_cache_release() -> put_page();
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---

...

>  extern pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
> @@ -425,7 +425,7 @@ static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
>  		return linear_hugepage_index(vma, address);
>  	pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
>  	pgoff += vma->vm_pgoff;
> -	return pgoff >> (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> +	return pgoff >> (PAGE_SHIFT - PAGE_SHIFT);
                        ^^^^^^^^^^^^^^^^^^^^^^^^^

Guenter