Re: [RFC] Making compound pages mandatory

[Andrew Morton <akpm@osdl.org>]

Linus Torvalds <torvalds@osdl.org> wrote:
>
> 
> 
> On Tue, 16 Nov 2004, David Howells wrote:
> > 
> > Do you have any objection to compound pages being made mandatory, even without
> > HUGETLB support?
> 
> I haven't really looked into it, so I cannot make an informed decision.  
> How big is the overhead? And what's the _point_, since we don't seem to 
> need them normally, but the code is there for people who _do_ need them? 

Yes, it's just the single pointer chase.  Probably that's the common case
now, because everyone will be enabling hugepages on lots of architectures.

But still, the non-compound code is well tested too, and leaving it in
place does make a little microoptimisation available to those who want it,
so I don't see a reason yet to make compound pages compulsory.

So I'd suggest that we make compound pages conditional on a new
CONFIG_COMPOUND_PAGE and make that equal to HUGETLB_PAGE || !MMU.