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SubjectRe: [PATCHv4 08/14] x86/mm: Make PGDIR_SHIFT and PTRS_PER_P4D variable
On Thu, Aug 17, 2017 at 01:10:05PM +0200, Ingo Molnar wrote:
>
> * Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> > On Thu, Aug 17, 2017 at 11:00:38AM +0200, Ingo Molnar wrote:
> > >
> > > * 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.
> >
> > This change increase vmlinux size for defconfig + X86_5LEVEL=y by ~4k or
> > 0.01%.
>
> Please add this info to one of the changelogs.
>
> BTW., some of that might be won back via the later optimizations, right?

Sorry, but no. Just chacked. Introducing alternatives increases .text
segment size by about 4k.

--
Kirill A. Shutemov

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