On 10/08/2012 11:16 PM, Mel Gorman wrote:

On Wed, Oct 03, 2012 at 08:56:14AM -0600, Mike Yoknis wrote:

quoted

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 sections to reduce the
number of loops executed.

Signed-off-by: Mike Yoknis <redacted>

This only helps SPARSEMEM and changes more headers than should be
necessary. It would have been easier to do something simple like

if (!early_pfn_valid(pfn)) {
	pfn = ALIGN(pfn + MAX_ORDER_NR_PAGES, MAX_ORDER_NR_PAGES) - 1;
	continue;
}

So if present memoy section in sparsemem can have 
MAX_ORDER_NR_PAGES-aligned range are all invalid?
If the answer is yes, when this will happen?

because that would obey the expectation that pages within a
MAX_ORDER_NR_PAGES-aligned range are all valid or all invalid (ARM is the
exception that breaks this rule). It would be less efficient on
SPARSEMEM than what you're trying to merge but I do not see the need for
the additional complexity unless you can show it makes a big difference
to boot times.

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