On Fri, 26 Oct 2012 16:47:47 -0600
Mike Yoknis <mike.yoknis@xxxxxx> wrote:
> memmap_init_zone() loops through every Page Frame Number (pfn),
> including pfn values that are within the gaps between existing
> memory sections. The unneeded looping will become a boot
> performance issue when machines configure larger memory ranges
> that will contain larger and more numerous gaps.
>
> The code will skip across invalid pfn values to reduce the
> number of loops executed.
>
So I was wondering how much difference this makes. Then I see Mel
already asked and was answered. The lesson: please treat a reviewer
question as a sign that the changelog needs more information! I added
this text to the changelog:
: We have what we call an "architectural simulator". It is a computer
: program that pretends that it is a computer system. We use it to test the
: firmware before real hardware is available. We have booted Linux on our
: simulator. As you would expect it takes longer to boot on the simulator
: than it does on real hardware.
:
: With my patch - boot time 41 minutes
: Without patch - boot time 94 minutes
:
: These numbers do not scale linearly to real hardware. But indicate to me
: a place where Linux can be improved.
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3857,8 +3857,11 @@ void __meminit memmap_init_zone(unsigned long
> size, int nid, unsigned long zone,
> * exist on hotplugged memory.
> */
> if (context == MEMMAP_EARLY) {
> - if (!early_pfn_valid(pfn))
> + if (!early_pfn_valid(pfn)) {
> + pfn = ALIGN(pfn + MAX_ORDER_NR_PAGES,
> + MAX_ORDER_NR_PAGES) - 1;
> continue;
> + }
> if (!early_pfn_in_nid(pfn, nid))
> continue;
> }
So what is the assumption here? That each zone's first page has a pfn
which is a multiple of MAX_ORDER_NR_PAGES?
That seems reasonable, but is it actually true, for all architectures
and for all time? Where did this come from?
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