Re: [PATCH v3 0/3] m68k/mm: switch from DISCONTIGMEM to SPARSEMEM

[Mike Rapoport <rppt@kernel.org>]

Hi Michael,

On Sat, Aug 22, 2020 at 11:27:18AM +1200, Michael Schmitz wrote:
> Hi Mike,
> 
> only tested on ARAnyM, but appears to work (after adding sparsemem.h and
> changing memblocks_present() to non-static).

Cool, thanks!
memblocks_present() is now called from sparse_init() and can be simply
dropped.

> 20 kB more total memory with sparsemem. Less memory used when booting
> to FastRAM, more used when booting to ST-RAM (checked right after boot
> on an idle system). The latter probably isn't significant.

When booting to FastRAM we still discard ST-RAM and only use it as
device memory for the framebuffer. So the total memory map size will be
smaller.

How many FastRAM do you have in your configuration?

> Cheers,
> 
> 	Michael
> 
> 
> Am 21.08.2020 um 19:56 schrieb Mike Rapoport:
> > On Fri, Aug 21, 2020 at 10:29:13AM +1200, Michael Schmitz wrote:
> > > Hi Mike,
> > > 
> > > Sorry, I had seen those but didn't get around to test in time.
> > > 
> > > Applying your patch series to Geert's v5.9-rc1, I get this:
> > > 
> > > >   CC      kernel/bounds.s
> > > >   CC      arch/m68k/kernel/asm-offsets.s
> > > > In file included from ./include/linux/mmzone.h:19,
> > > >                  from ./include/linux/topology.h:33,
> > > >                  from ./include/linux/irq.h:19,
> > > >                  from ./include/asm-generic/hardirq.h:13,
> > > >                  from ./arch/m68k/include/generated/asm/hardirq.h:1,
> > > >                  from ./include/linux/hardirq.h:10,
> > > >                  from ./include/linux/interrupt.h:11,
> > > >                  from ./include/linux/kernel_stat.h:9,
> > > >                  from arch/m68k/kernel/asm-offsets.c:16:
> > > > ./include/linux/page-flags-layout.h:28:10: fatal error: asm/sparsemem.h:
> > > > No such file or directory
> > > >  #include <asm/sparsemem.h>
> > > >           ^~~~~~~~~~~~~~~~~
> > > > compilation terminated.
> > > > make[2]: *** [arch/m68k/kernel/asm-offsets.s] Error 1
> > > > make[1]: *** [prepare0] Error 2
> > > > make: *** [__sub-make] Error 2
> > > 
> > > Your patch announcement blurb hat sparsemem.h listed among the changed
> > > files, but none of the three patches stats reference that file. Am I missing
> > > a prerequisite here?
> > 
> > Argh, I forgot to 'git add asm/sparsemem.h'.
> > I'll resend a refreshed version in a couple of days.
> > 
> > > Cheers,
> > > 
> > >     Michael
> > > 
> > > 
> > > On 21/08/20 4:03 AM, Mike Rapoport wrote:
> > > > Gentle ping :)
> > > > 
> > > > On Sat, Jul 18, 2020 at 07:26:48PM +0300, Mike Rapoport wrote:
> > > > > From: Mike Rapoport <rppt@linux.ibm.com>
> > > > > 
> > > > > Hi,
> > > > > 
> > > > > It took me a while to get back to this, but better late than never :)
> > > > > 
> > > > > These patches 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
> > > > > several megabytes.
> > > > > 
> > > > > 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.
> > > > > Yet, we cannot use smaller sections and still be able to address the entire
> > > > > 4G of the physical memory because the section number is encoded in the page
> > > > > flags and there are only 8 bits available.
> > > > > 
> > > > > For systems with several small memory chunks and with small (several megs)
> > > > > holes between them, 16M section size would cause wasted parts in the memory
> > > > > map and it is desirable to allow smaller section size at the expense of
> > > > > limiting the addressable memory.
> > > > > 
> > > > > I've hesitated between adding Kconfig option as Finn suggested [1] and
> > > > > other options like SPARSE_VMEMMAP or ARCH_HAS_HOLES_MEMORYMODEL. In the
> > > > > end, I think Kconfig is the simplest one from the implementation point of
> > > > > view and would work fine for people that run mainline kernels on vintage
> > > > > hardware.
> > > > > 
> > > > > For the systems with ST-RAM and FastRAM, the switch to SPARSEMEM does not
> > > > > change the limitation that if the kernel is loaded into the FastRam the
> > > > > ST-RAM remains unmapped. It only ensures that if the kernel is loaded in
> > > > > ST-RAM, the memory map is allocated from high physical addresses and then
> > > > > atari/stram.c is able to reserve the frame buffer memory. If the kernel is
> > > > > loaded to FastRAM, the ST-RAM remains unmapped as with DISCONTIGMEM and the
> > > > > atari/stram.c maps it as IOMEM.
> > > > > 
> > > > > [1] https://marc.info/?l=linux-m68k&m=156309170500921&w=2
> > > > > 
> > > > > v3 changes:
> > > > > * rebase on the current upstream
> > > > > * alias ARCH_PFN_BASE to m68k_memory[0].addr
> > > > > * add configuration option to allow two variants of section size.
> > > > > 
> > > > > v2 changes:
> > > > > * rebase on the current upstream
> > > > > * make ColdFire MMU select SINGLE_MEMORY_CHUNK in Kconfig.cpu
> > > > > 
> > > > > Mike Rapoport (3):
> > > > >    m68k/mm: make node data and node setup depend on CONFIG_DISCONTIGMEM
> > > > >    m68k/mm: enable use of generic memory_model.h for !DISCONTIGMEM
> > > > >    m68k/mm: switch from DISCONTIGMEM to SPARSEMEM
> > > > > 
> > > > >   arch/m68k/Kconfig.cpu               | 14 ++++++--
> > > > >   arch/m68k/include/asm/page.h        |  2 ++
> > > > >   arch/m68k/include/asm/page_mm.h     |  6 +++-
> > > > >   arch/m68k/include/asm/q.h   |  8 +++++
> > > > >   arch/m68k/include/asm/virtconvert.h |  2 +-
> > > > >   arch/m68k/mm/init.c                 |  8 ++---
> > > > >   arch/m68k/mm/motorola.c             | 64 ++++++++++++++++++++++++++++++-------
> > > > >   7 files changed, 84 insertions(+), 20 deletions(-)
> > > > >   create mode 100644 arch/m68k/include/asm/sparsemem.h
> > > > > 
> > > > > --
> > > > > 2.7.4
> > > > > 
> > > > > 
> > > > > *** BLURB HERE ***
> > > > > 
> > > > > Mike Rapoport (3):
> > > > >    m68k/mm: make node data and node setup depend on CONFIG_DISCONTIGMEM
> > > > >    m68k/mm: enable use of generic memory_model.h for !DISCONTIGMEM
> > > > >    m68k/mm: switch from DISCONTIGMEM to SPARSEMEM
> > > > > 
> > > > >   arch/m68k/Kconfig.cpu               | 23 ++++++++++++++---
> > > > >   arch/m68k/include/asm/page.h        |  2 ++
> > > > >   arch/m68k/include/asm/page_mm.h     |  7 +++++-
> > > > >   arch/m68k/include/asm/virtconvert.h |  2 +-
> > > > >   arch/m68k/mm/init.c                 |  8 +++---
> > > > >   arch/m68k/mm/motorola.c             | 39 ++++++++++++++++++++++++++---
> > > > >   6 files changed, 69 insertions(+), 12 deletions(-)
> > > > > 
> > > > > --
> > > > > 2.26.2
> > > > > 
> > 

-- 
Sincerely yours,
Mike.