On Wed 23-08-17 11:44:39, Chen Yu wrote:

On Tue, Aug 22, 2017 at 02:55:39PM +0200, Rafael J. Wysocki wrote:

quoted

On Tuesday, August 22, 2017 5:20:02 AM CEST Chen Yu wrote:

[...]

quoted

quoted

 void mark_free_pages(struct zone *zone)
 {
-	unsigned long pfn, max_zone_pfn;
+	unsigned long pfn, max_zone_pfn, page_num = 0;

+	unsigned long pfn, max_zone_pfn, page_count = WD_PAGE_COUNT;

quoted

 	unsigned long flags;
 	unsigned int order, t;
 	struct page *page;

@@ -2552,6 +2559,9 @@ void mark_free_pages(struct zone *zone)
 		if (pfn_valid(pfn)) {
 			page = pfn_to_page(pfn);
 
+			if (!((page_num++) % WD_INTERVAL_PAGE))
+				touch_nmi_watchdog();
+

->

	if (!--page_count) {
		touch_nmi_watchdog();
		page_count = WD_PAGE_COUNT;
	}

I guess this is to avoid the possible overflow if the page number is too large?

Even if the page_count overflown it wouldn't be a problem because of the
unsigned arithmetic. To be honest I find yours modulo based approach
easier to follow. Maybe it even compiles to a better code but I haven't
checked. Anyway one way or the other both ways are reasonable so
whatever Rafael (as the maintainer) prefers.

-- 
Michal Hocko
SUSE Labs

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