Re: [RFC] Cachemap for 2.6.12rc4-mm1. Was Re: [PATCH] enhance x86 MTRR handling

Dave Hansen
2005-05-13T14:24:56Z

On Fri, 2005-05-13 at 15:29 +0200, Andi Kleen wrote:
> > : x86-64 will need updating to also take advantage of this.
> > It may be able to just copy the i386 includes as-is, I've
> > not looked closely at the PAT related changes on x86-64 yet. Andi?
> >
> > : The list manipulation macros in mm/cachemap.c are a little fugly.
> >
> > Anything else ?
>
> For memory (pfn_valid == 1) it would be more memory efficient to use a few bits
> in struct page->flags

I think page->flags use should be limited to things that are relatively
performance-sensitive and arch-independent, mostly because we're running
out of them on 32-bit platforms, fast.

Each incremental use of page flags doesn't have any immediate storage
cost, but it's a serious pain when we run out, and having to bloat it to
a 64-bit value on 32-bit platforms wouldn't be very memory efficient,
either. :)

> In general because there are lots of uses of "range lists" it would be better
> to put it as a library into lib.

Either that, or something like "Dynamically allocated pageflags" would
be nice.

http://lwn.net/Articles/124332/

-- Dave