[PATCH RFC 12/19] mm: encode freetype flags in pageblock flags

[Brendan Jackman]

In preparation for implementing allocation from FREETYPE_UNMAPPED lists.

Since it works nicely with the existing allocator logic, and also offers
a simple way to amortize TLB flushing costs, __GFP_UNMAPPED will be
implemented by changing mappings at pageblock granularity. Therefore,
encode the mapping state in the pageblock flags.

Also add the necessary logic to record this from a freetype, and
reconstruct a freetype from the pageblock flags.

Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
---
 include/linux/pageblock-flags.h | 10 ++++++++++
 mm/page_alloc.c                 | 33 +++++++++++++++++++++++++--------
 2 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index 9a6c3ea17684d..b634280050071 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -11,6 +11,8 @@
 #ifndef PAGEBLOCK_FLAGS_H
 #define PAGEBLOCK_FLAGS_H
 
+#include <linux/freetype.h>
+#include <linux/log2.h>
 #include <linux/types.h>
 
 /* Bit indices that affect a whole block of pages */
@@ -18,6 +20,9 @@ enum pageblock_bits {
 	PB_migrate_0,
 	PB_migrate_1,
 	PB_migrate_2,
+	PB_freetype_flags,
+	PB_freetype_flags_end = PB_freetype_flags + NUM_FREETYPE_FLAGS - 1,
+
 	PB_compact_skip,/* If set the block is skipped by compaction */
 
 #ifdef CONFIG_MEMORY_ISOLATION
@@ -37,6 +42,7 @@ enum pageblock_bits {
 #define NR_PAGEBLOCK_BITS (roundup_pow_of_two(__NR_PAGEBLOCK_BITS))
 
 #define PAGEBLOCK_MIGRATETYPE_MASK (BIT(PB_migrate_0)|BIT(PB_migrate_1)|BIT(PB_migrate_2))
+#define PAGEBLOCK_FREETYPE_FLAGS_MASK (((1 << NUM_FREETYPE_FLAGS) - 1) << PB_freetype_flags)
 
 #ifdef CONFIG_MEMORY_ISOLATION
 #define PAGEBLOCK_ISO_MASK	BIT(PB_migrate_isolate)
@@ -44,6 +50,10 @@ enum pageblock_bits {
 #define PAGEBLOCK_ISO_MASK	0
 #endif
 
+#define PAGEBLOCK_FREETYPE_MASK (PAGEBLOCK_MIGRATETYPE_MASK | \
+				 PAGEBLOCK_ISO_MASK | \
+				 PAGEBLOCK_FREETYPE_FLAGS_MASK)
+
 #if defined(CONFIG_HUGETLB_PAGE)
 
 #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9635433c7d711..b79f81b64d9d7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -392,11 +392,8 @@ get_pfnblock_bitmap_bitidx(const struct page *page, unsigned long pfn,
 	unsigned long *bitmap;
 	unsigned long word_bitidx;
 
-#ifdef CONFIG_MEMORY_ISOLATION
-	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 8);
-#else
-	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
-#endif
+	/* NR_PAGEBLOCK_BITS must divide word size. */
+	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4 && NR_PAGEBLOCK_BITS != 8);
 	BUILD_BUG_ON(__MIGRATE_TYPE_END > PAGEBLOCK_MIGRATETYPE_MASK);
 	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
 
@@ -469,9 +466,20 @@ __always_inline freetype_t
 __get_pfnblock_freetype(const struct page *page, unsigned long pfn,
 			bool ignore_iso)
 {
-	int mt = get_pfnblock_migratetype(page, pfn);
+	unsigned long mask = PAGEBLOCK_FREETYPE_MASK;
+	enum migratetype migratetype;
+	unsigned int ft_flags;
+	unsigned long flags;
 
-	return migrate_to_freetype(mt, 0);
+	flags = __get_pfnblock_flags_mask(page, pfn, mask);
+	ft_flags = (flags & PAGEBLOCK_FREETYPE_FLAGS_MASK) >> PB_freetype_flags;
+
+	migratetype = flags & PAGEBLOCK_MIGRATETYPE_MASK;
+#ifdef CONFIG_MEMORY_ISOLATION
+	if (!ignore_iso && flags & BIT(PB_migrate_isolate))
+		migratetype = MIGRATE_ISOLATE;
+#endif
+	return migrate_to_freetype(migratetype, ft_flags);
 }
 
 /**
@@ -605,6 +613,15 @@ static void set_pageblock_migratetype(struct page *page,
 				  PAGEBLOCK_MIGRATETYPE_MASK | PAGEBLOCK_ISO_MASK);
 }
 
+static inline void set_pageblock_freetype_flags(struct page *page,
+						unsigned int ft_flags)
+{
+	unsigned int flags = ft_flags << PB_freetype_flags;
+
+	__set_pfnblock_flags_mask(page, page_to_pfn(page), flags,
+				  PAGEBLOCK_FREETYPE_FLAGS_MASK);
+}
+
 void __meminit init_pageblock_migratetype(struct page *page,
 					  enum migratetype migratetype,
 					  bool isolate)
@@ -628,7 +645,7 @@ void __meminit init_pageblock_migratetype(struct page *page,
 		flags |= BIT(PB_migrate_isolate);
 #endif
 	__set_pfnblock_flags_mask(page, page_to_pfn(page), flags,
-				  PAGEBLOCK_MIGRATETYPE_MASK | PAGEBLOCK_ISO_MASK);
+				  PAGEBLOCK_FREETYPE_MASK);
 }
 
 #ifdef CONFIG_DEBUG_VM

-- 
2.51.2