On Tue, Apr 12, 2022 at 02:05:51PM -0700, David Rientjes wrote:
> On Tue, 12 Apr 2022, Andrew Morton wrote:
>
> > On Tue, 12 Apr 2022 13:16:23 -0700 Sudarshan Rajagopalan <quic_sudaraja@xxxxxxxxxxx> wrote:
> >
> > > Check if pfn is valid before or not before moving it to freelist.
> > >
> > > There are possible scenario where a pageblock can have partial physical
> > > hole and partial part of System RAM. This happens when base address in RAM
> > > partition table is not aligned to pageblock size.
> > >
> > > ...
> > >
> > >
> > > Signed-off-by: Sudarshan Rajagopalan <quic_sudaraja@xxxxxxxxxxx>
> > > Fixes: 4c7b9896621be ("mm: remove pfn_valid_within() and CONFIG_HOLES_IN_ZONE")
> >
> > I made that 859a85ddf90e714092dea71a0e54c7b9896621be and added
> > cc:stable. I'll await reviewer input before proceeding further.
> >
>
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
>
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -2521,6 +2521,11 @@ static int move_freepages(struct zone *zone,
> > > int pages_moved = 0;
> > >
> > > for (pfn = start_pfn; pfn <= end_pfn;) {
> > > + if (!pfn_valid(pfn)) {
> >
> > Readers will wonder how we can encounter an invalid pfn here. A small
> > comment might help clue them in.
> >
>
> Sudarshan can correct me if I'm wrong, but this has to do with the
> pageblock alignment of the caller that assumes all pages in the range has
> an underlying struct page that we can access but that fails to hold true
> when we have a memory hole. A comment would definitely help:
We do have a struct page for every page in a pageblock even if there is a
hole in the physical memory. If this is not the case, there is more
fundamental bug that should be fixed.
> /* Pageblock alignment may cause us to try to access into a hole */
>
> > > + pfn++;
> > > + continue;
> > > + }
> > > +
> > > page = pfn_to_page(pfn);
> > > if (!PageBuddy(page)) {
> > > /*
> >
> >
> >
--
Sincerely yours,
Mike.
