Messages in this thread | | | From | Penttilä Mika <> | Subject | RE: [PATCH] x86_64: do not assume head_64.S used 4KB pages when !use_pse | Date | Thu, 23 Jun 2011 14:50:23 +0000 |
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> From: Stefano Stabellini [mailto:stefano.stabellini@eu.citrix.com] > Sent: 23. kesäkuuta 2011 15:57 > To: Penttilä Mika > Cc: Stefano Stabellini; linux-kernel@vger.kernel.org > Subject: Re: [PATCH] x86_64: do not assume head_64.S used 4KB pages > when !use_pse > > On Thu, 23 Jun 2011, Penttilä Mika wrote: > > > From: Stefano Stabellini <stefano.stabellini@eu.citrix.com> > > > > > head_64.S, which sets up the initial page table on x86_64, is not > aware > > > of PSE being enabled or disabled and it always allocates the > initial > > > mapping using 2MB pages. > > > > > Therefore on x86_64 find_early_table_space shouldn't update the > amount > > > of pages needed for pte pages depending on the size of the initial > > > mapping, because we know for sure that no pte pages have been > allocated > > > yet. > > > > > Signed-off-by: Stefano Stabellini > <stefano.stabellini@eu.citrix.com> > > > Reported-by: Ingo Molnar <mingo@elte.hu> > > > --- > > > arch/x86/mm/init.c | 7 +++++++ > > > 1 files changed, 7 insertions(+), 0 deletions(-) > > > > > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c > > > index 36bacfe..1e3098b 100644 > > > --- a/arch/x86/mm/init.c > > > +++ b/arch/x86/mm/init.c > > > @@ -42,12 +42,19 @@ static void __init > find_early_table_space(unsigned long start, > > > (PMD_SIZE * PTRS_PER_PMD)); > > > pmd_mapped *= (PMD_SIZE * PTRS_PER_PMD); > > > > > > + /* > > > + * On x86_64 do not limit the size we need to cover with 4KB > pages > > > + * depending on the initial allocation because head_64.S always > uses > > > + * 2MB pages. > > > + */ > > > +#ifdef CONFIG_X86_32 > > > if (start < PFN_PHYS(max_pfn_mapped)) { > > > if (PFN_PHYS(max_pfn_mapped) < end) > > > size -= PFN_PHYS(max_pfn_mapped) - start; > > > else > > > size = 0; > > > } > > > +#endif > > > > And arch/x86/mm/init.c also has: > > > > #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KMEMCHECK) > > /* > > * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use > small pages. > > * This will simplify cpa(), which otherwise needs to support > splitting > > * large pages into small in interrupt context, etc. > > */ > > use_pse = use_gbpages = 0; > > #else > > use_pse = cpu_has_pse; > > use_gbpages = direct_gbpages; > > #endif > > > > > > So big pages are also not used for DEBUG_PAGEALLOC and KMEMCHECK > configs even if head_32.S did. > > Right, but that is not a problem because head_32.S always uses 4KB > pages.
We use large pages FOR PAE kernels on x86-32 there
--Mika
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