[RFC PATCH 4/5] mm/page_alloc: add fixed migratetype pageblock infrastructure

[js1304]

From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

Following patch will support permanent migratetype pageblock by
kernel boot parameter. For preparation, this patch adds infrastructure
for it. Once fixed, migratetype cannot be changed anymore until power off.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 include/linux/pageblock-flags.h |  3 ++-
 mm/page_alloc.c                 | 12 +++++++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index e942558..0cf2c1f 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -31,12 +31,13 @@ enum pageblock_bits {
 	PB_migrate_end = PB_migrate + 3 - 1,
 			/* 3 bits required for migrate types */
 	PB_migrate_skip,/* If set the block is skipped by compaction */
+	PB_migrate_fixed,
 
 	/*
 	 * Assume the bits will always align on a word. If this assumption
 	 * changes then get/set pageblock needs updating.
 	 */
-	NR_PAGEBLOCK_BITS
+	NR_PAGEBLOCK_BITS = 8,
 };
 
 #ifdef CONFIG_HUGETLB_PAGE
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a167754..6b60e26 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -427,7 +427,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
 	unsigned long bitidx, word_bitidx;
 	unsigned long old_word, word;
 
-	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
+	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 8);
 
 	bitmap = get_pageblock_bitmap(page, pfn);
 	bitidx = pfn_to_bitidx(page, pfn);
@@ -451,10 +451,17 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
 
 void set_pageblock_migratetype(struct page *page, int migratetype)
 {
+	int fixed;
+
 	if (unlikely(page_group_by_mobility_disabled &&
 		     migratetype < MIGRATE_PCPTYPES))
 		migratetype = MIGRATE_UNMOVABLE;
 
+	fixed = get_pageblock_flags_group(page,
+			PB_migrate_fixed, PB_migrate_fixed);
+	if (fixed)
+		return;
+
 	set_pageblock_flags_group(page, (unsigned long)migratetype,
 					PB_migrate, PB_migrate_end);
 }
@@ -2026,6 +2033,9 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
 	int mt;
 	unsigned long max_managed, flags;
 
+	/* FIXME: disable highatomic pageblock reservation for test */
+	return;
+
 	/*
 	 * Limit the number reserved to 1 pageblock or roughly 1% of a zone.
 	 * Check is race-prone but harmless.
-- 
1.9.1