Re: [PATCH v4 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid()

[Mike Rapoport <rppt@linux.ibm.com>]

On Wed, May 12, 2021 at 09:00:02AM +0200, Ard Biesheuvel wrote:
> On Tue, 11 May 2021 at 12:05, Mike Rapoport <rppt@kernel.org> wrote:
> >
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > Hi,
> >
> > These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire
> > pfn_valid_within() to 1.
> >
> > The idea is to mark NOMAP pages as reserved in the memory map and restore
> > the intended semantics of pfn_valid() to designate availability of struct
> > page for a pfn.
> >
> > With this the core mm will be able to cope with the fact that it cannot use
> > NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER blocks
> > will be treated correctly even without the need for pfn_valid_within.
> >
> > The patches are boot tested on qemu-system-aarch64.
> >
> 
> Did you use EFI boot when testing this? The memory map is much more
> fragmented in that case, so this would be a good data point.

Right, something like this:

[    0.000000] Early memory node ranges                                         
[    0.000000]   node   0: [mem 0x0000000040000000-0x00000000ffffbfff]          
[    0.000000]   node   0: [mem 0x00000000ffffc000-0x00000000ffffffff]          
[    0.000000]   node   0: [mem 0x0000000100000000-0x00000004386fffff]          
[    0.000000]   node   0: [mem 0x0000000438700000-0x000000043899ffff]          
[    0.000000]   node   0: [mem 0x00000004389a0000-0x00000004389bffff]          
[    0.000000]   node   0: [mem 0x00000004389c0000-0x0000000438b5ffff]          
[    0.000000]   node   0: [mem 0x0000000438b60000-0x000000043be3ffff]          
[    0.000000]   node   0: [mem 0x000000043be40000-0x000000043becffff]          
[    0.000000]   node   0: [mem 0x000000043bed0000-0x000000043bedffff]          
[    0.000000]   node   0: [mem 0x000000043bee0000-0x000000043bffffff]          
[    0.000000]   node   0: [mem 0x000000043c000000-0x000000043fffffff]          

This is a pity really, because I don't see a fundamental reason for those
tiny holes all over the place. 

I know that EFI/ACPI mandates "IO style" memory access for those regions,
but I fail to get why...
 
> > I beleive it would be best to route these via mmotm tree.
> >
> > v4:
> > * rebase on v5.13-rc1
> >
> > v3: Link: https://lore.kernel.org/lkml/20210422061902.21614-1-rppt@kernel.org
> > * Fix minor issues found by Anshuman
> > * Freshen up the declaration of pfn_valid() to make it consistent with
> >   pfn_is_map_memory()
> > * Add more Acked-by and Reviewed-by tags, thanks Anshuman and David
> >
> > v2: Link: https://lore.kernel.org/lkml/20210421065108.1987-1-rppt@kernel.org
> > * Add check for PFN overflow in pfn_is_map_memory()
> > * Add Acked-by and Reviewed-by tags, thanks David.
> >
> > v1: Link: https://lore.kernel.org/lkml/20210420090925.7457-1-rppt@kernel.org
> > * Add comment about the semantics of pfn_valid() as Anshuman suggested
> > * Extend comments about MEMBLOCK_NOMAP, per Anshuman
> > * Use pfn_is_map_memory() name for the exported wrapper for
> >   memblock_is_map_memory(). It is still local to arch/arm64 in the end
> >   because of header dependency issues.
> >
> > rfc: Link: https://lore.kernel.org/lkml/20210407172607.8812-1-rppt@kernel.org
> >
> > Mike Rapoport (4):
> >   include/linux/mmzone.h: add documentation for pfn_valid()
> >   memblock: update initialization of reserved pages
> >   arm64: decouple check whether pfn is in linear map from pfn_valid()
> >   arm64: drop pfn_valid_within() and simplify pfn_valid()
> >
> >  arch/arm64/Kconfig              |  3 ---
> >  arch/arm64/include/asm/memory.h |  2 +-
> >  arch/arm64/include/asm/page.h   |  3 ++-
> >  arch/arm64/kvm/mmu.c            |  2 +-
> >  arch/arm64/mm/init.c            | 14 +++++++++++++-
> >  arch/arm64/mm/ioremap.c         |  4 ++--
> >  arch/arm64/mm/mmu.c             |  2 +-
> >  include/linux/memblock.h        |  4 +++-
> >  include/linux/mmzone.h          | 11 +++++++++++
> >  mm/memblock.c                   | 28 ++++++++++++++++++++++++++--
> >  10 files changed, 60 insertions(+), 13 deletions(-)
> >
> >
> > base-commit: 6efb943b8616ec53a5e444193dccf1af9ad627b5
> > --
> > 2.28.0
> >

-- 
Sincerely yours,
Mike.