[RFC PATCH 1/8] mm: page_alloc: add reserved THP pageblock type

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

Introduce a new migratetype MIGRATE_RESERVED_THP in preparation for the
upcoming Reserved THP feature.

Add specific handling in the page allocation and freeing paths (e.g.,
free_unref_folios() and __free_frozen_pages()) to prevent these reserved
pageblocks from being freed to the per-CPU (PCP) lists or being used by
other allocation contexts. Also, add statistical counters in the zone
structure and expose them in /proc/zoneinfo.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 include/linux/mmzone.h | 11 ++++++++---
 mm/page_alloc.c        | 16 +++++++++++++++-
 mm/show_mem.c          |  5 +++++
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ca27121871475..4418d0c9accdc 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -133,10 +133,9 @@ enum migratetype {
 	 * __free_pageblock_cma() function.
 	 */
 	MIGRATE_CMA,
-	__MIGRATE_TYPE_END = MIGRATE_CMA,
-#else
-	__MIGRATE_TYPE_END = MIGRATE_HIGHATOMIC,
 #endif
+	MIGRATE_RESERVED_THP,
+	__MIGRATE_TYPE_END = MIGRATE_RESERVED_THP,
 #ifdef CONFIG_MEMORY_ISOLATION
 	MIGRATE_ISOLATE,	/* can't allocate from here */
 #endif
@@ -161,6 +160,9 @@ extern const char * const migratetype_names[MIGRATE_TYPES];
 #  define is_migrate_cma_folio(folio, pfn) false
 #endif
 
+#define is_migrate_reserved_thp(migratetype) \
+	unlikely((migratetype) == MIGRATE_RESERVED_THP)
+
 static inline bool is_migrate_movable(int mt)
 {
 	return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
@@ -975,6 +977,9 @@ struct zone {
 	unsigned long nr_reserved_highatomic;
 	unsigned long nr_free_highatomic;
 
+	unsigned long nr_reserved_thp;
+	unsigned long nr_free_reserved_thp;
+
 	/*
 	 * We don't know if the memory that we're going to allocate will be
 	 * freeable or/and it will be released eventually, so to avoid totally
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ee902a468c2f5..613a711305072 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -263,6 +263,7 @@ const char * const migratetype_names[MIGRATE_TYPES] = {
 #ifdef CONFIG_CMA
 	"CMA",
 #endif
+	"ReserveTHP",
 #ifdef CONFIG_MEMORY_ISOLATION
 	"Isolate",
 #endif
@@ -784,6 +785,9 @@ static inline void account_freepages(struct zone *zone, int nr_pages,
 	else if (migratetype == MIGRATE_HIGHATOMIC)
 		WRITE_ONCE(zone->nr_free_highatomic,
 			   zone->nr_free_highatomic + nr_pages);
+	else if (migratetype == MIGRATE_RESERVED_THP)
+		WRITE_ONCE(zone->nr_free_reserved_thp,
+			   zone->nr_free_reserved_thp + nr_pages);
 }
 
 /* Used for pages not on another list */
@@ -2960,7 +2964,8 @@ static void __free_frozen_pages(struct page *page, unsigned int order,
 	zone = page_zone(page);
 	migratetype = get_pfnblock_migratetype(page, pfn);
 	if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
-		if (unlikely(is_migrate_isolate(migratetype))) {
+		if (unlikely(is_migrate_reserved_thp(migratetype) ||
+			     is_migrate_isolate(migratetype))) {
 			free_one_page(zone, page, pfn, order, fpi_flags);
 			return;
 		}
@@ -3038,6 +3043,7 @@ void free_unref_folios(struct folio_batch *folios)
 
 		/* Different zone requires a different pcp lock */
 		if (zone != locked_zone ||
+		    is_migrate_reserved_thp(migratetype) ||
 		    is_migrate_isolate(migratetype)) {
 			if (pcp) {
 				pcp_spin_unlock(pcp);
@@ -3045,6 +3051,12 @@ void free_unref_folios(struct folio_batch *folios)
 				pcp = NULL;
 			}
 
+			if (is_migrate_reserved_thp(migratetype)) {
+				free_one_page(zone, &folio->page, pfn,
+					      order, FPI_NONE);
+				continue;
+			}
+
 			/*
 			 * Free isolated pages directly to the
 			 * allocator, see comment in free_frozen_pages.
@@ -3568,6 +3580,8 @@ static inline long __zone_watermark_unusable_free(struct zone *z,
 	if (likely(!(alloc_flags & ALLOC_RESERVES)))
 		unusable_free += READ_ONCE(z->nr_free_highatomic);
 
+	unusable_free += READ_ONCE(z->nr_free_reserved_thp);
+
 #ifdef CONFIG_CMA
 	/* If allocation can't use CMA areas don't use free CMA pages */
 	if (!(alloc_flags & ALLOC_CMA))
diff --git a/mm/show_mem.c b/mm/show_mem.c
index 43aca5a2ac990..e9381afca4aca 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -142,6 +142,7 @@ static void show_migration_types(unsigned char type)
 #ifdef CONFIG_CMA
 		[MIGRATE_CMA]		= 'C',
 #endif
+		[MIGRATE_RESERVED_THP]	= 'T',
 #ifdef CONFIG_MEMORY_ISOLATION
 		[MIGRATE_ISOLATE]	= 'I',
 #endif
@@ -308,6 +309,8 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 			" high:%lukB"
 			" reserved_highatomic:%luKB"
 			" free_highatomic:%luKB"
+			" reserved_thp:%luKB"
+			" free_reserved_thp:%luKB"
 			" active_anon:%lukB"
 			" inactive_anon:%lukB"
 			" active_file:%lukB"
@@ -331,6 +334,8 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 			K(high_wmark_pages(zone)),
 			K(zone->nr_reserved_highatomic),
 			K(zone->nr_free_highatomic),
+			K(zone->nr_reserved_thp),
+			K(zone->nr_free_reserved_thp),
 			K(zone_page_state(zone, NR_ZONE_ACTIVE_ANON)),
 			K(zone_page_state(zone, NR_ZONE_INACTIVE_ANON)),
 			K(zone_page_state(zone, NR_ZONE_ACTIVE_FILE)),
-- 
2.54.0