linux-kernel - [PATCH v1 3/4] mm/memory_hotplug: Simplify online_pages

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Date:   Fri,  9 Aug 2019 14:57:00 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: [PATCH v1 3/4] mm/memory_hotplug: Simplify online_pages_range()

move_pfn_range_to_zone() will set all pages to PG_reserved via
memmap_init_zone(). The only way a page could no longer be reserved
would be if a MEM_GOING_ONLINE notifier would clear PG_reserved - which
is not done (the online_page callback is used for that purpose by
e.g., Hyper-V instead). walk_system_ram_range() will never call
online_pages_range() with duplicate PFNs, so drop the PageReserved() check.

Simplify the handling, as online_pages always corresponds to nr_pages.
There is no need for online_pages_blocks() anymore.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Pavel Tatashin <pasha.tatashin@...een.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/memory_hotplug.c | 42 ++++++++++++++++++------------------------
 1 file changed, 18 insertions(+), 24 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2abd938c8c45..87f85597a19e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -632,37 +632,31 @@ static void generic_online_page(struct page *page, unsigned int order)
 #endif
 }
 
-static int online_pages_blocks(unsigned long start, unsigned long nr_pages)
+static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
+			void *arg)
 {
-	unsigned long end = start + nr_pages;
-	int order, onlined_pages = 0;
+	const unsigned long end_pfn = start_pfn + nr_pages;
+	unsigned long pfn;
+	int order;
 
-	while (start < end) {
-		order = min(MAX_ORDER - 1,
-			get_order(PFN_PHYS(end) - PFN_PHYS(start)));
+	/*
+	 * Online the pages. The callback might decide to keep some pages
+	 * PG_reserved (to add them to the buddy later), but we still account
+	 * them as being online/belonging to this zone ("present").
+	 */
+	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
+		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
 		/* make sure the PFN is aligned and we don't exceed the range */
-		while (!IS_ALIGNED(start, 1ul << order) ||
-		       (1ul << order) > end - start)
+		while (!IS_ALIGNED(start_pfn, 1ul << order) ||
+		       (1ul << order) > end_pfn - pfn)
 			order--;
-		(*online_page_callback)(pfn_to_page(start), order);
-
-		onlined_pages += (1UL << order);
-		start += (1UL << order);
+		(*online_page_callback)(pfn_to_page(pfn), order);
 	}
-	return onlined_pages;
-}
-
-static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
-			void *arg)
-{
-	unsigned long onlined_pages = *(unsigned long *)arg;
-
-	if (PageReserved(pfn_to_page(start_pfn)))
-		onlined_pages += online_pages_blocks(start_pfn, nr_pages);
 
-	online_mem_sections(start_pfn, start_pfn + nr_pages);
+	/* mark all involved sections as online */
+	online_mem_sections(start_pfn, end_pfn);
 
-	*(unsigned long *)arg = onlined_pages;
+	*(unsigned long *)arg += nr_pages;
 	return 0;
 }
 
-- 
2.21.0