include/linux/page-flags-layout.h

   1 #ifndef PAGE_FLAGS_LAYOUT_H
   2 #define PAGE_FLAGS_LAYOUT_H
   3
   4 #include <linux/numa.h>
   5 #include <generated/bounds.h>
   6
   7 /*
   8  * When a memory allocation must conform to specific limitations (such
   9  * as being suitable for DMA) the caller will pass in hints to the
  10  * allocator in the gfp_mask, in the zone modifier bits.  These bits
  11  * are used to select a priority ordered list of memory zones which
  12  * match the requested limits. See gfp_zone() in include/linux/gfp.h
  13  */
  14 #if MAX_NR_ZONES < 2
  15 #define ZONES_SHIFT 0
  16 #elif MAX_NR_ZONES <= 2
  17 #define ZONES_SHIFT 1
  18 #elif MAX_NR_ZONES <= 4
  19 #define ZONES_SHIFT 2
  20 #else
  21 #error ZONES_SHIFT -- too many zones configured adjust calculation
  22 #endif
  23
  24 #ifdef CONFIG_SPARSEMEM
  25 #include <asm/sparsemem.h>
  26
  27 /* SECTION_SHIFT        #bits space required to store a section # */
  28 #define SECTIONS_SHIFT  (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
  29
  30 #endif /* CONFIG_SPARSEMEM */
  31
  32 /*
  33  * page->flags layout:
  34  *
  35  * There are five possibilities for how page->flags get laid out.  The first
  36  * pair is for the normal case without sparsemem. The second pair is for
  37  * sparsemem when there is plenty of space for node and section information.
  38  * The last is when there is insufficient space in page->flags and a separate
  39  * lookup is necessary.
  40  *
  41  * No sparsemem or sparsemem vmemmap: |       NODE     | ZONE |          ... | FLAGS |
  42  *         " plus space for last_nid: |       NODE     | ZONE | LAST_NID ... | FLAGS |
  43  * classic sparse with space for node:| SECTION | NODE | ZONE |          ... | FLAGS |
  44  *         " plus space for last_nid: | SECTION | NODE | ZONE | LAST_NID ... | FLAGS |
  45  * classic sparse no space for node:  | SECTION |     ZONE    | ... | FLAGS |
  46  */
  47 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
  48 #define SECTIONS_WIDTH          SECTIONS_SHIFT
  49 #else
  50 #define SECTIONS_WIDTH          0
  51 #endif
  52
  53 #define ZONES_WIDTH             ZONES_SHIFT
  54
  55 #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
  56 #define NODES_WIDTH             NODES_SHIFT
  57 #else
  58 #ifdef CONFIG_SPARSEMEM_VMEMMAP
  59 #error "Vmemmap: No space for nodes field in page flags"
  60 #endif
  61 #define NODES_WIDTH             0
  62 #endif
  63
  64 #ifdef CONFIG_NUMA_BALANCING
  65 #define LAST_NID_SHIFT NODES_SHIFT
  66 #else
  67 #define LAST_NID_SHIFT 0
  68 #endif
  69
  70 #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_NID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
  71 #define LAST_NID_WIDTH LAST_NID_SHIFT
  72 #else
  73 #define LAST_NID_WIDTH 0
  74 #endif
  75
  76 /*
  77  * We are going to use the flags for the page to node mapping if its in
  78  * there.  This includes the case where there is no node, so it is implicit.
  79  */
  80 #if !(NODES_WIDTH > 0 || NODES_SHIFT == 0)
  81 #define NODE_NOT_IN_PAGE_FLAGS
  82 #endif
  83
  84 #if defined(CONFIG_NUMA_BALANCING) && LAST_NID_WIDTH == 0
  85 #define LAST_NID_NOT_IN_PAGE_FLAGS
  86 #endif
  87
  88 #endif /* _LINUX_PAGE_FLAGS_LAYOUT */