1 files changed, 88 insertions, 0 deletions

diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
new file mode 100644
index 000000000000..93506a114034
--- /dev/null
+++ b/include/linux/page-flags-layout.h
@@ -0,0 +1,88 @@
+#ifndef PAGE_FLAGS_LAYOUT_H
+#define PAGE_FLAGS_LAYOUT_H
+
+#include <linux/numa.h>
+#include <generated/bounds.h>
+
+/*
+ * When a memory allocation must conform to specific limitations (such
+ * as being suitable for DMA) the caller will pass in hints to the
+ * allocator in the gfp_mask, in the zone modifier bits.  These bits
+ * are used to select a priority ordered list of memory zones which
+ * match the requested limits. See gfp_zone() in include/linux/gfp.h
+ */
+#if MAX_NR_ZONES < 2
+#define ZONES_SHIFT 0
+#elif MAX_NR_ZONES <= 2
+#define ZONES_SHIFT 1
+#elif MAX_NR_ZONES <= 4
+#define ZONES_SHIFT 2
+#else
+#error ZONES_SHIFT -- too many zones configured adjust calculation
+#endif
+
+#ifdef CONFIG_SPARSEMEM
+#include <asm/sparsemem.h>
+
+/* SECTION_SHIFT        #bits space required to store a section # */
+#define SECTIONS_SHIFT  (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
+
+#endif /* CONFIG_SPARSEMEM */
+
+/*
+ * page->flags layout:
+ *
+ * There are five possibilities for how page->flags get laid out.  The first
+ * pair is for the normal case without sparsemem. The second pair is for
+ * sparsemem when there is plenty of space for node and section information.
+ * The last is when there is insufficient space in page->flags and a separate
+ * lookup is necessary.
+ *
+ * No sparsemem or sparsemem vmemmap: |       NODE     | ZONE |          ... | FLAGS |
+ *         " plus space for last_nid: |       NODE     | ZONE | LAST_NID ... | FLAGS |
+ * classic sparse with space for node:| SECTION | NODE | ZONE |          ... | FLAGS |
+ *         " plus space for last_nid: | SECTION | NODE | ZONE | LAST_NID ... | FLAGS |
+ * classic sparse no space for node:  | SECTION |     ZONE    | ... | FLAGS |
+ */
+#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
+#define SECTIONS_WIDTH          SECTIONS_SHIFT
+#else
+#define SECTIONS_WIDTH          0
+#endif
+
+#define ZONES_WIDTH             ZONES_SHIFT
+
+#if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
+#define NODES_WIDTH             NODES_SHIFT
+#else
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+#error "Vmemmap: No space for nodes field in page flags"
+#endif
+#define NODES_WIDTH             0
+#endif
+
+#ifdef CONFIG_NUMA_BALANCING
+#define LAST_NID_SHIFT NODES_SHIFT
+#else
+#define LAST_NID_SHIFT 0
+#endif
+
+#if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_NID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
+#define LAST_NID_WIDTH LAST_NID_SHIFT
+#else
+#define LAST_NID_WIDTH 0
+#endif
+
+/*
+ * We are going to use the flags for the page to node mapping if its in
+ * there.  This includes the case where there is no node, so it is implicit.
+ */
+#if !(NODES_WIDTH > 0 || NODES_SHIFT == 0)
+#define NODE_NOT_IN_PAGE_FLAGS
+#endif
+
+#if defined(CONFIG_NUMA_BALANCING) && LAST_NID_WIDTH == 0
+#define LAST_NID_NOT_IN_PAGE_FLAGS
+#endif
+
+#endif /* _LINUX_PAGE_FLAGS_LAYOUT */