Re: Hot/cold allocation -- swsusp can not handle hot pages

[Andrew Morton]

Pavel Machek wrote:
> 
> Hi!
> 
> > > Swsusp counts free pages, and relies on fact that when it allocates
> > > page there's one free page less. That is no longer true with hot
> > > pages.
> > > I attempted to work it around but it seems I am getting hot pages even
> > > when I ask for cold one. This seems to fix it. Does it looks like
> > > "possibly mergable" patch?
> > > --- clean/mm/page_alloc.c   2002-11-01 00:37:44.000000000 +0100
> > > +++ linux-swsusp/mm/page_alloc.c    2002-11-01 22:53:47.000000000 +0100
> > > @@ -361,7 +361,7 @@
> > >     unsigned long flags;
> > >     struct page *page = NULL;
> > >
> > > -   if (order == 0) {
> > > +   if ((order == 0) && !cold) {
> > >             struct per_cpu_pages *pcp;
> > >
> > >             pcp = &zone->pageset[get_cpu()].pcp[cold];
> > >
> >
> > This doesn't seem to be doing what you want, even if it seems to work.
> > If you want there to be one free page less, then allocating it will
> > work regardless. What are you looking for besides that? If it's not
> > already working you want some additional semantics. Could this involve
> > is_head_of_free_region()? That should be solvable with a per-cpu list
> > shootdown algorithm to fully merge all the buddy bitmap things.
> 
> I need pages I allocate to disappear from "is_head_of_free_region()",
> so my counts match.
> 

hm.  swsusp does funny things.  Would it be posible to get a
big-picture "how this whole thing works" story?  What exactly
is the nature of its relationship with the page allocator?

I'm not really sure what to suggest here.  Emptying the per-cpu
page pools would be tricky.  Maybe a swsusp-special page allocator
which goes direct to the buddy lists or something.