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SubjectRe: [PATCHv4 08/14] x86/mm: Make PGDIR_SHIFT and PTRS_PER_P4D variable

* Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote:

> For boot-time switching between 4- and 5-level paging we need to be able
> to fold p4d page table level at runtime. It requires variable
> PGDIR_SHIFT and PTRS_PER_P4D.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> arch/x86/boot/compressed/kaslr.c | 5 +++++
> arch/x86/include/asm/pgtable_32.h | 2 ++
> arch/x86/include/asm/pgtable_32_types.h | 2 ++
> arch/x86/include/asm/pgtable_64_types.h | 15 +++++++++++++--
> arch/x86/kernel/head64.c | 9 ++++++++-
> arch/x86/mm/dump_pagetables.c | 12 +++++-------
> arch/x86/mm/init_64.c | 2 +-
> arch/x86/mm/kasan_init_64.c | 2 +-
> arch/x86/platform/efi/efi_64.c | 4 ++--
> include/asm-generic/5level-fixup.h | 1 +
> include/asm-generic/pgtable-nop4d.h | 1 +
> include/linux/kasan.h | 2 +-
> mm/kasan/kasan_init.c | 2 +-
> 13 files changed, 43 insertions(+), 16 deletions(-)

So I'm wondering what the code generation effect of this is - what's the
before/after vmlinux size?

My guess is that the effect should be very small, as these constants are not
widely used - but I'm only guessing and could be wrong.

Thanks,

Ingo

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