Re: [RFC] Remove unswappable anonymous pages off the LRU

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 15 Feb 2007 18:50:39 -0800 (PST) Christoph Lameter <clameter@sgi.com> wrote:

> On Thu, 15 Feb 2007, Andrew Morton wrote:
> 
> > We discussed that a while back and iirc ia64 has gone and gobbled most of
> > the upper 32bits.  Someone went and added some ascii art around the
> > PG_uncached definition but it is incomprehensible.  It seems to claim that
> > ia64 has gone and used all 32 bits, dammit.  If so, some adjustments to
> > ia64 might be called for.
> 
> Yes ia64 has used the upper 32 bit. However, the lower 32 bits are fully 
> usable. So we have 32-20 = 12 bits to play with on 64 bit.

OK.  But not many things are 64-bit-only?

> > 
> > > page_type = { SLAB, LRU, MLOCK, RESERVED, BUDDY, <add 3 more types here> }
> > 
> > Yeah, maybe.  There doesn't seem to be a lot of room for that though - a
> > lot of those flags are quite independent and can occur simultaneously.
> 
> None of the above can occur simultaneously.

<actually pays attention>

OK.

The actual implementation details might get messy though.  We can do a
non-atomic rmw of the three bits but that could corrupt a concurrent
modification of a different flag.  Or we could do a succession of three
set_bit/clear_bit operations, but that exposes intermediate invalid states.

It can be done I guess, but it'd be fiddly.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>