linux-kernel - [PATCH v1] mm/memory_hotplug: move debug_pagealloc_map_pages() into online_pages

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Message-ID: <20241202110108.451522-1-david@redhat.com>
Date: Mon,  2 Dec 2024 12:01:08 +0100
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>
Subject: [PATCH v1] mm/memory_hotplug: move debug_pagealloc_map_pages() into online_pages_range()

In the near future, we want to have a single way to handover PageOffline
pages to the buddy, whereby they could have:

(a) Never been exposed to the buddy before: kept PageOffline when onlining
    the memory block.
(b) Been allocated from the buddy, for example using
    alloc_contig_range() to then be set PageOffline,

Let's start by making generic_online_page() less special compared to
ordinary page freeing (e.g., free_contig_range()), and perform the
debug_pagealloc_map_pages() call unconditionally, even when the online
callback might decide to keep the pages offline.

All pages are already initialized with PageOffline, so nobody touches
them either way.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Oscar Salvador <osalvador@...e.de>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/memory_hotplug.c | 10 +++++++++-
 mm/page_alloc.c     |  6 ------
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c43b4e7fb298..20af14e695c7 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -650,6 +650,7 @@ static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages)
 	 * this and the first chunk to online will be pageblock_nr_pages.
 	 */
 	for (pfn = start_pfn; pfn < end_pfn;) {
+		struct page *page = pfn_to_page(pfn);
 		int order;
 
 		/*
@@ -664,7 +665,14 @@ static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages)
 		else
 			order = MAX_PAGE_ORDER;
 
-		(*online_page_callback)(pfn_to_page(pfn), order);
+		/*
+		 * Exposing the page to the buddy by freeing can cause
+		 * issues with debug_pagealloc enabled: some archs don't
+		 * like double-unmappings. So treat them like any pages that
+		 * were allocated from the buddy.
+		 */
+		debug_pagealloc_map_pages(page, 1 << order);
+		(*online_page_callback)(page, order);
 		pfn += (1UL << order);
 	}
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cc3296cf8c95..01927f03af0b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1293,12 +1293,6 @@ void __meminit __free_pages_core(struct page *page, unsigned int order,
 			set_page_count(p, 0);
 		}
 
-		/*
-		 * Freeing the page with debug_pagealloc enabled will try to
-		 * unmap it; some archs don't like double-unmappings, so
-		 * map it first.
-		 */
-		debug_pagealloc_map_pages(page, nr_pages);
 		adjust_managed_page_count(page, nr_pages);
 	} else {
 		for (loop = 0; loop < nr_pages; loop++, p++) {
-- 
2.47.1