[PATCH RESEND v1] mm/memory_hotplug: move debug_pagealloc_map_pages() into online_pages_range()

[PATCH RESEND v1] mm/memory_hotplug: move debug_pagealloc_map_pages() into online_pages_range()

[David Hildenbrand]

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@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: David Hildenbrand <david@redhat.com>
---

SMTP server issues, resending so it reaches linux-mm as well.

---
 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

Re: [PATCH RESEND v1] mm/memory_hotplug: move debug_pagealloc_map_pages() into online_pages_range()

[Oscar Salvador]

On Tue, Dec 03, 2024 at 11:20:50AM +0100, David Hildenbrand wrote:
> 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

This got me confused for a moment. I'd have said "making
__free_pages_core" less special? As that is where we were calling 
debug_pagealloc_map_pages() if the context  on the context.

> 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@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Oscar Salvador <osalvador@suse.de>


-- 
Oscar Salvador
SUSE Labs

Re: [PATCH RESEND v1] mm/memory_hotplug: move debug_pagealloc_map_pages() into online_pages_range()

[David Hildenbrand]

On 03.12.24 16:28, Oscar Salvador wrote:
> On Tue, Dec 03, 2024 at 11:20:50AM +0100, David Hildenbrand wrote:
>> 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
> 
> This got me confused for a moment. I'd have said "making
> __free_pages_core" less special? As that is where we were calling
> debug_pagealloc_map_pages() if the context  on the context.

Well, yes, but it's really generic_online_page()->__free_pages_core() 
that triggers this exact code only.

@Andrew, can you fix that up?

s/generic_online_page()/generic_online_page()->__free_pages_core()/

> 
>> 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@linux-foundation.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> Acked-by: Oscar Salvador <osalvador@suse.de>

Thanks!

-- 
Cheers,

David / dhildenb