linux-kernel - Re: [PATCH -mm] mm: refactor page index/offset getters

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Date:	Wed, 23 Jul 2014 17:45:54 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH -mm] mm: refactor page index/offset getters

On Wed, Jul 23, 2014 at 02:39:18PM -0700, Andrew Morton wrote:
> On Tue, 15 Jul 2014 12:41:12 -0400 Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:
> 
> > There is a complaint about duplication around the fundamental routines
> > of page index/offset getters.
> > 
> > page_(index|offset) and page_file_(index|offset) provide the same
> > functionality, so we can merge them as page_(index|offset), respectively.
> > 
> > And this patch gives the clear meaning to the getters:
> >  - page_index(): get page cache index (offset in relevant page size)
> >  - page_pgoff(): get 4kB page offset
> >  - page_offset(): get byte offset
> > All these functions are aware of regular pages, swapcaches, and hugepages.
> > 
> > The definition of PageHuge is relocated to include/linux/mm.h, because
> > some users of page_pgoff() doesn't include include/linux/hugetlb.h.
> > 
> > __page_file_index() is not well named, because it's only for swap cache.
> > So let's rename it with __page_swap_index().
> 
> Thanks, I guess that's better.  Could others please have a look-n-think?
> 
> I did this:
> 
> --- a/include/linux/pagemap.h~mm-refactor-page-index-offset-getters-fix
> +++ a/include/linux/pagemap.h
> @@ -412,7 +412,7 @@ static inline pgoff_t page_pgoff(struct
>  }
>  
>  /*
> - * Return the byte offset of the given page.
> + * Return the file offset of the given pagecache page, in bytes.

Thanks, it's clearer.

>  static inline loff_t page_offset(struct page *page)
>  {
> 
> 
> 
> You had a random xfs_aops.c whitespace fix which I'll pretend I didn't
> notice ;)

I just couldn't resist fixing it ;)
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