Messages in this thread | | | Date | Thu, 28 Sep 2017 13:17:37 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv7 09/19] x86/mm: Make MAX_PHYSADDR_BITS and MAX_PHYSMEM_BITS dynamic |
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On Thu, Sep 28, 2017 at 10:25:14AM +0200, Ingo Molnar wrote: > > * Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote: > > > For boot-time switching between paging modes, we need to be able to > > adjust size of physical address space at runtime. > > > > As part of making physical address space size variable, we have to make > > X86_5LEVEL dependent on SPARSEMEM_VMEMMAP. !SPARSEMEM_VMEMMAP > > configuration doesn't work well with variable MAX_PHYSMEM_BITS. > > > > Affect on kernel image size: > > > > text data bss dec hex filename > > 10710340 4880000 860160 16450500 fb03c4 vmlinux.before > > 10710666 4880000 860160 16450826 fb050a vmlinux.after > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > --- > > arch/x86/Kconfig | 1 + > > arch/x86/include/asm/pgtable_64_types.h | 2 +- > > arch/x86/include/asm/sparsemem.h | 9 ++------- > > arch/x86/kernel/setup.c | 5 ++--- > > 4 files changed, 6 insertions(+), 11 deletions(-) > > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 6a15297140ff..f75723d62c25 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -1403,6 +1403,7 @@ config X86_PAE > > config X86_5LEVEL > > bool "Enable 5-level page tables support" > > depends on X86_64 > > + depends on SPARSEMEM_VMEMMAP > > Adding a 'depends on' to random kernel internal implementational details, to > support new hardware, sucks as an UI, as it will just randomly hide/show the new > hardware option if certain magic Kconfig combinations are set. > > Please check how other architectures are doing it. (Hint: they are using select.) > > Also, what is the real dependency here? Why don't the other memory models work, > what's the failure mode - won't build, won't boot, or misbehaves in some other > way?
I won't build.
For !SPARSEMEM_VMEMMAP SECTIONS_WIDTH depends on MAX_PHYSMEM_BITS:
SECTIONS_WIDTH SECTIONS_SHIFT MAX_PHYSMEM_BITS
And SECTIONS_WIDTH is used on per-processor stage, it doesn't work if it's dyncamic. See include/linux/page-flags-layout.h.
-- Kirill A. Shutemov
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