mm/page_alloc: pageblock flags functions clean up

Patch series "Make MIGRATE_ISOLATE a standalone bit", v10.

This patchset moves MIGRATE_ISOLATE to a standalone bit to avoid being
overwritten during pageblock isolation process.  Currently,
MIGRATE_ISOLATE is part of enum migratetype (in include/linux/mmzone.h),
thus, setting a pageblock to MIGRATE_ISOLATE overwrites its original
migratetype.  This causes pageblock migratetype loss during
alloc_contig_range() and memory offline, especially when the process fails
due to a failed pageblock isolation and the code tries to undo the
finished pageblock isolations.

In terms of performance for changing pageblock types, no performance
change is observed:

1. I used perf to collect stats of offlining and onlining all memory
   of a 40GB VM 10 times and see that get_pfnblock_flags_mask() and
   set_pfnblock_flags_mask() take about 0.12% and 0.02% of the whole
   process respectively with and without this patchset across 3 runs.

2. I used perf to collect stats of dd from /dev/random to a 40GB tmpfs
   file and find get_pfnblock_flags_mask() takes about 0.05% of the
   process with and without this patchset across 3 runs.


This patch (of 6):

No functional change is intended.

1. Add __NR_PAGEBLOCK_BITS for the number of pageblock flag bits and use
   roundup_pow_of_two(__NR_PAGEBLOCK_BITS) as NR_PAGEBLOCK_BITS to take
   right amount of bits for pageblock flags.
2. Rename PB_migrate_skip to PB_compact_skip.
3. Add {get,set,clear}_pfnblock_bit() to operate one a standalone bit,
   like PB_compact_skip.
3. Make {get,set}_pfnblock_flags_mask() internal functions and use
   {get,set}_pfnblock_migratetype() for pageblock migratetype operations.
4. Move pageblock flags common code to get_pfnblock_bitmap_bitidx().
3. Use MIGRATETYPE_MASK to get the migratetype of a pageblock from its
   flags.
4. Use PB_migrate_end in the definition of MIGRATETYPE_MASK instead of
   PB_migrate_bits.
5. Add a comment on is_migrate_cma_folio() to prevent one from changing it
   to use get_pageblock_migratetype() and causing issues.

Link: https://lkml.kernel.org/r/20250617021115.2331563-1-ziy@nvidia.com
Link: https://lkml.kernel.org/r/20250617021115.2331563-2-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shuemov <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Richard Chang <richardycc@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 132 insertions, 39 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 31041e2aa33a..43a4c1532721 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -353,81 +353,174 @@ static inline int pfn_to_bitidx(const struct page *page, unsigned long pfn)
 	return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
 }
 
+static __always_inline bool is_standalone_pb_bit(enum pageblock_bits pb_bit)
+{
+	return pb_bit > PB_migrate_end && pb_bit < __NR_PAGEBLOCK_BITS;
+}
+
+static __always_inline void
+get_pfnblock_bitmap_bitidx(const struct page *page, unsigned long pfn,
+			   unsigned long **bitmap_word, unsigned long *bitidx)
+{
+	unsigned long *bitmap;
+	unsigned long word_bitidx;
+
+	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
+	BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));
+	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
+
+	bitmap = get_pageblock_bitmap(page, pfn);
+	*bitidx = pfn_to_bitidx(page, pfn);
+	word_bitidx = *bitidx / BITS_PER_LONG;
+	*bitidx &= (BITS_PER_LONG - 1);
+	*bitmap_word = &bitmap[word_bitidx];
+}
+
+
 /**
- * get_pfnblock_flags_mask - Return the requested group of flags for the pageblock_nr_pages block of pages
+ * __get_pfnblock_flags_mask - Return the requested group of flags for
+ * a pageblock_nr_pages block of pages
  * @page: The page within the block of interest
  * @pfn: The target page frame number
  * @mask: mask of bits that the caller is interested in
  *
  * Return: pageblock_bits flags
  */
-unsigned long get_pfnblock_flags_mask(const struct page *page,
-					unsigned long pfn, unsigned long mask)
+static unsigned long __get_pfnblock_flags_mask(const struct page *page,
+					       unsigned long pfn,
+					       unsigned long mask)
 {
-	unsigned long *bitmap;
-	unsigned long bitidx, word_bitidx;
+	unsigned long *bitmap_word;
+	unsigned long bitidx;
 	unsigned long word;
 
-	bitmap = get_pageblock_bitmap(page, pfn);
-	bitidx = pfn_to_bitidx(page, pfn);
-	word_bitidx = bitidx / BITS_PER_LONG;
-	bitidx &= (BITS_PER_LONG-1);
+	get_pfnblock_bitmap_bitidx(page, pfn, &bitmap_word, &bitidx);
 	/*
-	 * This races, without locks, with set_pfnblock_flags_mask(). Ensure
+	 * This races, without locks, with set_pfnblock_migratetype(). Ensure
 	 * a consistent read of the memory array, so that results, even though
 	 * racy, are not corrupted.
 	 */
-	word = READ_ONCE(bitmap[word_bitidx]);
+	word = READ_ONCE(*bitmap_word);
 	return (word >> bitidx) & mask;
 }
 
-static __always_inline int get_pfnblock_migratetype(const struct page *page,
-					unsigned long pfn)
+/**
+ * get_pfnblock_bit - Check if a standalone bit of a pageblock is set
+ * @page: The page within the block of interest
+ * @pfn: The target page frame number
+ * @pb_bit: pageblock bit to check
+ *
+ * Return: true if the bit is set, otherwise false
+ */
+bool get_pfnblock_bit(const struct page *page, unsigned long pfn,
+		      enum pageblock_bits pb_bit)
 {
-	return get_pfnblock_flags_mask(page, pfn, MIGRATETYPE_MASK);
+	unsigned long *bitmap_word;
+	unsigned long bitidx;
+
+	if (WARN_ON_ONCE(!is_standalone_pb_bit(pb_bit)))
+		return false;
+
+	get_pfnblock_bitmap_bitidx(page, pfn, &bitmap_word, &bitidx);
+
+	return test_bit(bitidx + pb_bit, bitmap_word);
 }
 
 /**
- * set_pfnblock_flags_mask - Set the requested group of flags for a pageblock_nr_pages block of pages
+ * get_pfnblock_migratetype - Return the migratetype of a pageblock
+ * @page: The page within the block of interest
+ * @pfn: The target page frame number
+ *
+ * Return: The migratetype of the pageblock
+ *
+ * Use get_pfnblock_migratetype() if caller already has both @page and @pfn
+ * to save a call to page_to_pfn().
+ */
+__always_inline enum migratetype
+get_pfnblock_migratetype(const struct page *page, unsigned long pfn)
+{
+	return __get_pfnblock_flags_mask(page, pfn, MIGRATETYPE_MASK);
+}
+
+/**
+ * __set_pfnblock_flags_mask - Set the requested group of flags for
+ * a pageblock_nr_pages block of pages
  * @page: The page within the block of interest
- * @flags: The flags to set
  * @pfn: The target page frame number
+ * @flags: The flags to set
  * @mask: mask of bits that the caller is interested in
  */
-void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
-					unsigned long pfn,
-					unsigned long mask)
+static void __set_pfnblock_flags_mask(struct page *page, unsigned long pfn,
+				      unsigned long flags, unsigned long mask)
 {
-	unsigned long *bitmap;
-	unsigned long bitidx, word_bitidx;
+	unsigned long *bitmap_word;
+	unsigned long bitidx;
 	unsigned long word;
 
-	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
-	BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));
-
-	bitmap = get_pageblock_bitmap(page, pfn);
-	bitidx = pfn_to_bitidx(page, pfn);
-	word_bitidx = bitidx / BITS_PER_LONG;
-	bitidx &= (BITS_PER_LONG-1);
-
-	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
+	get_pfnblock_bitmap_bitidx(page, pfn, &bitmap_word, &bitidx);
 
 	mask <<= bitidx;
 	flags <<= bitidx;
 
-	word = READ_ONCE(bitmap[word_bitidx]);
+	word = READ_ONCE(*bitmap_word);
 	do {
-	} while (!try_cmpxchg(&bitmap[word_bitidx], &word, (word & ~mask) | flags));
+	} while (!try_cmpxchg(bitmap_word, &word, (word & ~mask) | flags));
+}
+
+/**
+ * set_pfnblock_bit - Set a standalone bit of a pageblock
+ * @page: The page within the block of interest
+ * @pfn: The target page frame number
+ * @pb_bit: pageblock bit to set
+ */
+void set_pfnblock_bit(const struct page *page, unsigned long pfn,
+		      enum pageblock_bits pb_bit)
+{
+	unsigned long *bitmap_word;
+	unsigned long bitidx;
+
+	if (WARN_ON_ONCE(!is_standalone_pb_bit(pb_bit)))
+		return;
+
+	get_pfnblock_bitmap_bitidx(page, pfn, &bitmap_word, &bitidx);
+
+	set_bit(bitidx + pb_bit, bitmap_word);
 }
 
-void set_pageblock_migratetype(struct page *page, int migratetype)
+/**
+ * clear_pfnblock_bit - Clear a standalone bit of a pageblock
+ * @page: The page within the block of interest
+ * @pfn: The target page frame number
+ * @pb_bit: pageblock bit to clear
+ */
+void clear_pfnblock_bit(const struct page *page, unsigned long pfn,
+			enum pageblock_bits pb_bit)
+{
+	unsigned long *bitmap_word;
+	unsigned long bitidx;
+
+	if (WARN_ON_ONCE(!is_standalone_pb_bit(pb_bit)))
+		return;
+
+	get_pfnblock_bitmap_bitidx(page, pfn, &bitmap_word, &bitidx);
+
+	clear_bit(bitidx + pb_bit, bitmap_word);
+}
+
+/**
+ * set_pageblock_migratetype - Set the migratetype of a pageblock
+ * @page: The page within the block of interest
+ * @migratetype: migratetype to set
+ */
+__always_inline void set_pageblock_migratetype(struct page *page,
+					       enum migratetype migratetype)
 {
 	if (unlikely(page_group_by_mobility_disabled &&
 		     migratetype < MIGRATE_PCPTYPES))
 		migratetype = MIGRATE_UNMOVABLE;
 
-	set_pfnblock_flags_mask(page, (unsigned long)migratetype,
-				page_to_pfn(page), MIGRATETYPE_MASK);
+	__set_pfnblock_flags_mask(page, page_to_pfn(page),
+				  (unsigned long)migratetype, MIGRATETYPE_MASK);
 }
 
 #ifdef CONFIG_DEBUG_VM
@@ -667,7 +760,7 @@ static inline void __add_to_free_list(struct page *page, struct zone *zone,
 	int nr_pages = 1 << order;
 
 	VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype,
-		     "page type is %lu, passed migratetype is %d (nr=%d)\n",
+		     "page type is %d, passed migratetype is %d (nr=%d)\n",
 		     get_pageblock_migratetype(page), migratetype, nr_pages);
 
 	if (tail)
@@ -693,7 +786,7 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
 
 	/* Free page moving can fail, so it happens before the type update */
 	VM_WARN_ONCE(get_pageblock_migratetype(page) != old_mt,
-		     "page type is %lu, passed migratetype is %d (nr=%d)\n",
+		     "page type is %d, passed migratetype is %d (nr=%d)\n",
 		     get_pageblock_migratetype(page), old_mt, nr_pages);
 
 	list_move_tail(&page->buddy_list, &area->free_list[new_mt]);
@@ -715,7 +808,7 @@ static inline void __del_page_from_free_list(struct page *page, struct zone *zon
 	int nr_pages = 1 << order;
 
         VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype,
-		     "page type is %lu, passed migratetype is %d (nr=%d)\n",
+		     "page type is %d, passed migratetype is %d (nr=%d)\n",
 		     get_pageblock_migratetype(page), migratetype, nr_pages);
 
 	/* clear reported state and update reported page count */
@@ -3123,7 +3216,7 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
 
 /*
  * Do not instrument rmqueue() with KMSAN. This function may call
- * __msan_poison_alloca() through a call to set_pfnblock_flags_mask().
+ * __msan_poison_alloca() through a call to set_pfnblock_migratetype().
  * If __msan_poison_alloca() attempts to allocate pages for the stack depot, it
  * may call rmqueue() again, which will result in a deadlock.
  */