linux-kernel - Re: [PATCH] x86-64: fix combining of regions in init_memory

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Date:	Sun, 14 Sep 2008 11:20:31 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Jan Beulich" <jbeulich@...ell.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64: fix combining of regions in init_memory_mapping()

On Fri, Sep 12, 2008 at 7:43 AM, Jan Beulich <jbeulich@...ell.com> wrote:
> When nr_range gets decremented, the same slot must be considered for
> coalescing with its new successor again.
>
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
>
> ---
>  arch/x86/mm/init_64.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- linux-2.6.27-rc6/arch/x86/mm/init_64.c      2008-08-29 10:53:00.000000000 +0200
> +++ 2.6.27-rc6-x86_64-mr-coalesce/arch/x86/mm/init_64.c 2008-09-12 11:58:45.000000000 +0200
> @@ -636,7 +636,7 @@ unsigned long __init_refok init_memory_m
>                old_start = mr[i].start;
>                memmove(&mr[i], &mr[i+1],
>                         (nr_range - 1 - i) * sizeof (struct map_range));
> -               mr[i].start = old_start;
> +               mr[i--].start = old_start;
>                nr_range--;
>        }
>

this patch seems not right.
Ingo, please don't apply it.

original code:
        /* try to merge same page size and continuous */
        for (i = 0; nr_range > 1 && i < nr_range - 1; i++) {
                unsigned long old_start;
                if (mr[i].end != mr[i+1].start ||
                    mr[i].page_size_mask != mr[i+1].page_size_mask)
                        continue;
                /* move it */
                old_start = mr[i].start;
                memmove(&mr[i], &mr[i+1],
                         (nr_range - 1 - i) * sizeof (struct map_range));
                mr[i].start = old_start;
                nr_range--;
        }

so it save old_start and first, and move entries forward (so old one
is overwriten), and put back old_start ...

YH
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