Re: [PATCH 1/2] mm: remove pfn_valid_within() and CONFIG_HOLES_IN_ZONE

[David Hildenbrand]

On 13.07.21 12:22, Mike Rapoport wrote:
> On Tue, Jul 13, 2021 at 11:51:46AM +0200, David Hildenbrand wrote:
> > On 13.07.21 10:00, Mike Rapoport wrote:
> > > From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > >
> > > After recent changes in freeing of the unused parts of the memory map and
> > > rework of pfn_valid() in arm and arm64 there are no architectures that can
> > > have holes in the memory map within a pageblock and so nothing can enable
> > > CONFIG_HOLES_IN_ZONE which guards non trivial implementation of
> > > pfn_valid_within().
> > >
> > > With that, pfn_valid_within() is always hardwired to 1 and can be
> > > completely removed.
> > >
> > > Remove calls to pfn_valid_within() and CONFIG_HOLES_IN_ZONE.
> > >
> > > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> >
> > There is currently the discussion to increase MAX_ORDER, for example, to
> > cover 1GiB instead of 4MiB on x86-64. This would mean that we could
> > suddenly, again, have holes insides MAX_ORDER - 1 pages.
> >
> > So I assume if we ever go down that path, we'll need something like this
> > again.
>
> It depends whether pageblock_order will be also increased. PFN walkers rely
> on continuity of pageblocks rather than MAX_ORDER chunks, so if
> pageblock_order won't change, there won't be need to check for pfn_valid()
> inside a pageblock.

I'm pushing for letting pageblocks stay untouched, so good to know!

(we still have this crazy special case of pageblocks > MAX_ORDER - 1 
right now, which I think we should just eliminate)

--
Thanks,

David / dhildenb