Hi Mike,
On Wed, Jun 19, 2019 at 9:06 AM Geert Uytterhoeven <[email protected]> wrote:
> On Tue, Jun 18, 2019 at 8:10 AM Mike Rapoport <[email protected]> wrote:
> > On Mon, Jun 17, 2019 at 10:00:32PM +0200, Geert Uytterhoeven wrote:
> > > On Thu, May 16, 2019 at 8:03 AM Mike Rapoport <[email protected]> wrote:
> > > > These pacthes replace DISCONTIGMEM with SPARSEMEM on m68k for systems
> > > > with
> > > > !SINGLE_MEMORY_CHUNK set.
> > > >
> > > > With SPARSEMEM there is a single node for the entire physical memory
> > > > and to
> > > > cope with holes in the physical address space it is divided to sections
> > > > of
> > > > up to 16M.
> > > >
> > > > Each section has it's own memory map which size depends on actual
> > > > populated
> > > > memory.
> > > >
> > > > The section size of 16M was chosen pretty much arbitrarily as I couldn't
> > > > find specs for systems with e.g. Zorro memory extensions.
>
> > > Unfortunately it crashes on my Amiga, cfr. the logs below.
> > >
> > > Then I realized the "section size of 16M". My Amiga has a single block
> > > of 12 MiB of FastRAM at 0x07400000, which is not aligned to 16 MiB.
> > > (Yes, base address of motherboard RAM is 0x08000000 - ramsize ;-)
> > >
> > > I've tried:
> > >
> > > -#define MAX_PHYSMEM_BITS 32
> > > -#define SECTION_SIZE_BITS 24
> > > +#define MAX_PHYSMEM_BITS 30
> > > +#define SECTION_SIZE_BITS 22
> > >
> > > but that doesn't seem to make a difference.
> > >
> > > Do you have a clue? Thanks!
> >
> > Not really, at least yet.
> > Can you please send the entire log with
> >
> > "mminit_loglevel=4 memblock=debug debug"
> >
> > in the command line?
>
> Attached, with debug_boot_weak_hash added, which reveals it's a real
> NULL (=0x0) pointer dereference.
>
> Looking at the disassembly, it happens in clear_page().
> Call chain:
>
> get_page_from_freelist()
> prep_new_page()
> clear_highpage()
> void *kaddr = kmap_atomic(page);
> clear_page(kaddr);
>
> get_page_from_freelist() verifies page is non-zero before calling
> prep_new_page(), so it must be the kmap_atomic() that returns NULL.
>
> kmap_atomic() basically does page_address(page).
> As m68k defines WANT_PAGE_VIRTUAL, that evaluates to page->virtual,
> which I assume to be NULL.
> Is there a call to set_page_address() missing in the sparsemem code?
>
> Questions:
> 1. Why does it work on Atari/ARAnyM?
> 2. Why does it work on SPARC64, which also uses WANT_PAGE_VIRTUAL
> and has SPARSEMEM support? (arc uses WANT_PAGE_VIRTUAL, but no
> SPARSEMEM)
Oh, I have CONFIG_SINGLE_MEMORY_CHUNK=y, so SPARSEMEM is
_not_ used.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
