Re: [RFC] Free up page->private for compound pages

[Christoph Lameter <clameter@sgi.com>]

On Thu, 5 Apr 2007, Hugh Dickins wrote:

> > I am not so much worried about performance but more about the availability 
> > of the page->private field of compound pages.
> 
> Yes, I realise that.  I meant
> 	if (unlikely(PageCompound(page)) && PageTail(page))
> shouldn't slow down the !PageCompound fast paths more than the existing
> 	if (unlikely(PageCompound(page)))
> or the
> 	if (unlikely(PageTail(page)))
> you had.

Right.

> > I think we cannot overload the page flag after all because of the page 
> > count issue you pointed out. Guess I should be cleaning up my 
> > initial patch and repost it?
> 
> I still think PageTail is not worth its own distinct page flag:

Well I think we just killed 2 flags for software suspend. Did I not earn 
at least one by being involved in that project? ;-)

> I can understand you drawing back from my page+1 suggestion,
> but I don't understand why you're so reluctant to say
> 	if (unlikely(PageCompound(page)) && PageTail(page))

Thats fine with me. Ahh.. This would solve the alias issue.... (Lights
going on). Okay we can overload after all. Need to add some comments 
though.


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