linux-kernel - Re: [PATCH] mm: introduce __linear_page

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Message-ID: <20130215150205.GC31037@dhcp22.suse.cz>
Date:	Fri, 15 Feb 2013 16:02:05 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Huang Shijie <b32955@...escale.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: introduce __linear_page_index()

On Tue 05-02-13 13:27:41, Andrew Morton wrote:
[...]
> > +static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
> > +					unsigned long address)
> > +{
> >  	if (unlikely(is_vm_hugetlb_page(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 __linear_page_index(vma, address) >>
> > +				(PAGE_CACHE_SHIFT - PAGE_SHIFT);
> >  }
> 
> I don't think we need bother creating both linear_page_index() and
> __linear_page_index().  Realistically, we won't be supporting
> PAGE_SHIFT!=PAGE_CACHE_SHIFT.  And most (or all?) of the sites which
> you changed should have been using PAGE_CACHE_SHIFT anyway!

Except for hugetlb (huge_pmd_share, unmap_ref_private) which uses
PAGE_SHIFT to get an index into mapping. History proves there was
some confusion about those in the past (36e4f20a fixing 0c176d52). So
__linear_page_index makes some sense here.

-- 
Michal Hocko
SUSE Labs
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