Re: [RFC] Making compound pages mandatory

[David Howells <dhowells@redhat.com>]

> > So I'd suggest that we make compound pages conditional on a new
> > CONFIG_COMPOUND_PAGE and make that equal to HUGETLB_PAGE || !MMU.
> 
> That sounds sane, and seems easily done in init/Kconfig. David?

That looks reasonable, I think.

Would you object to some more micro-optimisations:

 (1) Allow struct page to be marked __attribute__((align(sizeof(long)*2))) on
     archs that want it. On frv for instance this would allow the use of
     double-register load/store instructions when accessing certain adjacent
     pairs of members (such as page->lru.next and page->lru.prev). I think the
     frv compiler will emit these when it knows it won't cause a misalignment
     exception (8-byte accesses must be 8-byte aligned).

 (2) Allow put_page() to be provided by the arch if desired. This would allow
     me to do a better job of testing page flags and mucking around with the
     refcount by writing it in assembly. This is sort of prerequisite on (1)
     and the fact that accesses to page->_count are atomic and so are inline
     asm anyway.

> [ There's too damn many Davids around. DavidH? Mr Howells? Dude? ]

I generally refer to all other Davids as Dave, apart from David Woodhouse who
should be referred to as "Fish":-P

DavidH would be okay.

David