Re: [PATCHv3 4/5] mm: make compound_head() robust

[Kirill A. Shutemov]

On Fri, Aug 21, 2015 at 11:11:27AM -0500, Christoph Lameter wrote:
> On Fri, 21 Aug 2015, Kirill A. Shutemov wrote:
> 
> > > Is this really true?  For example if it's a slab page, will that page
> > > ever be inspected by code which is looking for the PageTail bit?
> >
> > +Christoph.
> >
> > What we know for sure is that space is not used in tail pages, otherwise
> > it would collide with current compound_dtor.
> 
> Sl*b allocators only do a virt_to_head_page on tail pages.

The question was whether it's safe to assume that the bit 0 is always zero
in the word as this bit will encode PageTail().

-- 
 Kirill A. Shutemov
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