On 02/06/20 at 06:56am, Wei Yang wrote:

On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:

quoted

Hi Wei Yang,

On 02/05/20 at 05:59pm, Wei Yang wrote:

quoted

quoted

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index f294918f7211..8dafa1ba8d9f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,

		if (pfn) {
			zone->zone_start_pfn = pfn;
			zone->spanned_pages = zone_end_pfn - pfn;
+		} else {
+			zone->zone_start_pfn = 0;
+			zone->spanned_pages = 0;
		}
	} else if (zone_end_pfn == end_pfn) {
		/*

@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,

					       start_pfn);
		if (pfn)
			zone->spanned_pages = pfn - zone_start_pfn + 1;
+		else {
+			zone->zone_start_pfn = 0;
+			zone->spanned_pages = 0;
+		}
	}

If it is me, I would like to take out these two similar logic out.

I also like this style. 

quoted

For example:

	if () {
	} else if () {
	} else {
		goto out;

Here the last else is unnecessary, right?

I am afraid not.

If the range is not the first or last, we would leave pfn not initialized.

Ah, you are right. I forgot that one. Then pfn can be assigned the
zone_start_pfn as the old code. Then the following logic is the same
as the original code, find_smallest_section_pfn()/find_biggest_section_pfn() 
have done the iteration the old for loop was doing.

	unsigned long pfn = zone_start_pfn;	
	if () {
	} else if () {
	} 

	/* The zone has no valid section */
	if (!pfn) {
        	zone->zone_start_pfn = 0;
        	zone->spanned_pages = 0;
	}