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    SubjectRe: x86/mm: Limit 2/4M size calculation to x86_32
    On 07/13/2012 06:41 AM, Stefan Bader wrote:
    > I was bisecting a problem on 64bit where any attempt to cause a crash kernel to
    > boot would hang. The bisect ended up on commit 722bc6b (x86/mm: Fix the size
    > calculation of mapping tables) and somehow, looking at the calling function and
    > the ranges printed on boot, I think the calculations should only be done in the
    > 32bit case.
    >
    > On 64bit:
    > [ 0.000000] init_memory_mapping: [mem 0x00000000-0x77e87fff]
    > [ 0.000000] [mem 0x00000000-0x77dfffff] page 2M
    > [ 0.000000] [mem 0x77e00000-0x77e87fff] page 4k
    >
    > Attached patch would fix this if you agree with it. Thanks.
    >

    Any news on this one? I thought it would be quite simple to check for sanity and
    not wasting memory sounds like a good thing to do. Even though there is plenty
    of it around most of the time. ;)

    -Stefan

    > -Stefan
    >
    >
    > From 6b679d1af20656929c0e829f29eed60b0a86a74f Mon Sep 17 00:00:00 2001
    > From: Stefan Bader <stefan.bader@canonical.com>
    > Date: Fri, 13 Jul 2012 15:16:33 +0200
    > Subject: [PATCH] x86/mm: Limit 2/4M size calculation to x86_32
    >
    > commit 722bc6b (x86/mm: Fix the size calculation of mapping tables)
    > did modify the extra space calculation for mapping tables in order
    > to make up for the first 2/4M memory range using 4K pages.
    > However this setup is only used when compiling for 32bit. On 64bit
    > there is only the trailing area of 4K pages (which is already added).
    >
    > The code was already adapted once for things went wrong on a 8TB
    > machine (bd2753b x86/mm: Only add extra pages count for the first memory
    > range during pre-allocation early page table space), but it looks a bit
    > like it currently would overdo things for 64bit.
    > I only noticed while bisecting for the reason I could not make a crash
    > kernel boot (which ended up on this patch).
    >
    > Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
    > Cc: WANG Cong <xiyou.wangcong@gmail.com>
    > Cc: Yinghai Lu <yinghai@kernel.org>
    > Cc: Tejun Heo <tj@kernel.org>
    > ---
    > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
    > index bc4e9d8..636bbfd 100644
    > --- a/arch/x86/mm/init.c
    > +++ b/arch/x86/mm/init.c
    > @@ -60,10 +60,11 @@ static void __init find_early_table_space(struct map_range
    > *mr, unsigned long en
    > extra = end - ((end>>PMD_SHIFT) << PMD_SHIFT);
    > #ifdef CONFIG_X86_32
    > extra += PMD_SIZE;
    > -#endif
    > +
    > /* The first 2/4M doesn't use large pages. */
    > if (mr->start < PMD_SIZE)
    > extra += mr->end - mr->start;
    > +#endif
    >
    > ptes = (extra + PAGE_SIZE - 1) >> PAGE_SHIFT;
    > } else
    >




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