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    SubjectRe: sparsemem panic in 2.6.17-rc5-mm1 and -mm2
    On Wed, 07 Jun 2006 15:36:25 +1000
    Rusty Russell <rusty@rustcorp.com.au> wrote:

    > On Tue, 2006-06-06 at 21:58 -0700, Andrew Morton wrote:
    > > On Wed, 7 Jun 2006 09:43:55 +0900
    > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > >
    > > > On Tue, 6 Jun 2006 00:27:58 -0700
    > > > Andrew Morton <akpm@osdl.org> wrote:
    > > >
    > > > >
    > > > > I tried sparsemem on my little x86 box here. Boots OK, after fixing up the
    > > > > kswapd_init() patch (below).
    > > > >
    > > > > I'm wondering why I have 4k of highmem:
    > > > >
    > > >
    > > > Could you show /proc/iomem of your 4k HIGHMEM box ?
    > > > Does 4k HIGHMEM exist only when SPARSEMEM is selected ?
    > >
    > > Turns out that my 4 kbyte highmem zone (at least, as reported in
    > > /proc/meminfo) is due to
    > >
    > > vdso-randomize-the-i386-vdso-by-moving-it-into-a-vma.patch
    >
    > Thanks for this report, Andrew!
    >
    > Yes, MAXMEM is reduced by one page in the patch, taking into account
    > that kernel memory tops out at __FIXADDR_TOP, not 0xFFFFFFFF. AFAICT
    > this is in fact a bugfix, which becomes more important when
    > __FIXADDR_TOP can be moved to create a larger memory hole (as for
    > hypervisors).
    >
    > You now have 1 page more memory available in your system.

    The kernel has differing opinions about that:

    BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
    BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
    BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
    BIOS-e820: 0000000000100000 - 0000000038000000 (usable)
    BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
    BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
    BIOS-e820: 00000000fffc0000 - 0000000100000000 (reserved)
    0MB HIGHMEM available.
    896MB LOWMEM available.

    > Use it
    > wisely.


    > I'm sure Gerd will slap me if I'm wrong on this. Here's the patch
    > fragment:
    >
    > -#define MAXMEM (-__PAGE_OFFSET-__VMALLOC_RESERVE)
    > +#define MAXMEM (__FIXADDR_TOP-__PAGE_OFFSET-__VMALLOC_RESERVE)

    Well. Applying this with `patch -R' would presumably restore the situation.
    But not having a clue why this change was made, I didn't bother trying it.

    From what you're saying, it appears that this patch is an unrelated change,
    to fix the off-by-one? And that if this machine had anything other than
    exactly 7*128MB of physical memory, I wouldn't have noticed?
    -
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