Re: [RFC][PATCH] Dynamically allocated pageflags.

[Nigel Cunningham <ncunningham@cyclades.com>]

Hi.

On Sat, 2005-02-19 at 14:02, Dave Hansen wrote:
> On Sat, 2005-02-19 at 13:43 +1100, Nigel Cunningham wrote:
> > For some time now, we've been running out of bits for pageflags.
> > 
> > In Suspend2, I need the functional equivalent of pageflags, but don't
> > need them when Suspend isn't running. One of the outcomes of the last
> > submission of Suspend2 for review was that I changed the format in which
> > that data is stored, creating something I call dynamically allocated
> > pageflags.
> > 
> > It's a simple idea: we tie together a bunch of order zero allocated
> > pages using a kmalloc'd list of poiinters to those pages, and store the
> > location of that kmalloc'd list in what's really an unsigned long **
> > (typedef'd). We also provide macros so that calls for setting and
> > clearing flags can look just like ordinary pageflag set/clear/test
> > invocations.
> > 
> > Helpers are also provided for allocating and freeing the maps.
> 
> I'm kicking myself because I thought about this 2 minutes after we
> talked on IRC.  

> One issue is that it doesn't work with DISCONTIGMEM (or the upcoming
> sparsemem).  max_mapnr doesn't exist on those systems, and on the really
> discontiguous ones, you might be allocating very large areas with very
> sparse maps.

:> Am I right in thinking that just requires something similar, done
per-zone? If that's the case, I'll happily modify the code to suit. I
should support discontig anyway in suspend.

> One thing that I've been thinking about for these things is something
> tree-based.  A 1 or 2-level tree, like pagetables should be fast enough,
> and handle the sparse and discontiguous layouts a little better than a
> flat one.  We could even do a flat bitmap for normal systems, and #ifdef
> in the table only when it's needed.  I can take a look at doing this
> next week.

Mmm. I've got enough on my plate at the mo, so I'll just wait to see
what you come up with.

Regards,

Nigel
-- 
Nigel Cunningham
Software Engineer, Canberra, Australia
http://www.cyclades.com

Ph: +61 (2) 6292 8028      Mob: +61 (417) 100 574