src/include/utils/freepage.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * freepage.h
   4  *        Management of page-organized free memory.
   5  *
   6  * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  * src/include/utils/freepage.h
  10  *
  11  *-------------------------------------------------------------------------
  12  */
  13
  14 #ifndef FREEPAGE_H
  15 #define FREEPAGE_H
  16
  17 #include "storage/lwlock.h"
  18 #include "utils/relptr.h"
  19
  20 /* Forward declarations. */
  21 typedef struct FreePageSpanLeader FreePageSpanLeader;
  22 typedef struct FreePageBtree FreePageBtree;
  23 typedef struct FreePageManager FreePageManager;
  24
  25 /*
  26  * PostgreSQL normally uses 8kB pages for most things, but many common
  27  * architecture/operating system pairings use a 4kB page size for memory
  28  * allocation, so we do that here also.
  29  */
  30 #define FPM_PAGE_SIZE                   4096
  31
  32 /*
  33  * Each freelist except for the last contains only spans of one particular
  34  * size.  Everything larger goes on the last one.  In some sense this seems
  35  * like a waste since most allocations are in a few common sizes, but it
  36  * means that small allocations can simply pop the head of the relevant list
  37  * without needing to worry about whether the object we find there is of
  38  * precisely the correct size (because we know it must be).
  39  */
  40 #define FPM_NUM_FREELISTS               129
  41
  42 /* Define relative pointer types. */
  43 relptr_declare(FreePageBtree, RelptrFreePageBtree);
  44 relptr_declare(FreePageManager, RelptrFreePageManager);
  45 relptr_declare(FreePageSpanLeader, RelptrFreePageSpanLeader);
  46
  47 /* Everything we need in order to manage free pages (see freepage.c) */
  48 struct FreePageManager
  49 {
  50         RelptrFreePageManager self;
  51         RelptrFreePageBtree btree_root;
  52         RelptrFreePageSpanLeader btree_recycle;
  53         unsigned        btree_depth;
  54         unsigned        btree_recycle_count;
  55         Size            singleton_first_page;
  56         Size            singleton_npages;
  57         Size            contiguous_pages;
  58         bool            contiguous_pages_dirty;
  59         RelptrFreePageSpanLeader freelist[FPM_NUM_FREELISTS];
  60 #ifdef FPM_EXTRA_ASSERTS
  61         /* For debugging only, pages put minus pages gotten. */
  62         Size            free_pages;
  63 #endif
  64 };
  65
  66 /* Macros to convert between page numbers (expressed as Size) and pointers. */
  67 #define fpm_page_to_pointer(base, page) \
  68         (AssertVariableIsOfTypeMacro(page, Size), \
  69          (base) + FPM_PAGE_SIZE * (page))
  70 #define fpm_pointer_to_page(base, ptr)          \
  71         (((Size) (((char *) (ptr)) - (base))) / FPM_PAGE_SIZE)
  72
  73 /* Macro to convert an allocation size to a number of pages. */
  74 #define fpm_size_to_pages(sz) \
  75         (((sz) + FPM_PAGE_SIZE - 1) / FPM_PAGE_SIZE)
  76
  77 /* Macros to check alignment of absolute and relative pointers. */
  78 #define fpm_pointer_is_page_aligned(base, ptr)          \
  79         (((Size) (((char *) (ptr)) - (base))) % FPM_PAGE_SIZE == 0)
  80 #define fpm_relptr_is_page_aligned(base, relptr)                \
  81         ((relptr).relptr_off % FPM_PAGE_SIZE == 0)
  82
  83 /* Macro to find base address of the segment containing a FreePageManager. */
  84 #define fpm_segment_base(fpm)   \
  85         (((char *) fpm) - fpm->self.relptr_off)
  86
  87 /* Macro to access a FreePageManager's largest consecutive run of pages. */
  88 #define fpm_largest(fpm) \
  89         (fpm->contiguous_pages)
  90
  91 /* Functions to manipulate the free page map. */
  92 extern void FreePageManagerInitialize(FreePageManager *fpm, char *base);
  93 extern bool FreePageManagerGet(FreePageManager *fpm, Size npages,
  94                                                            Size *first_page);
  95 extern void FreePageManagerPut(FreePageManager *fpm, Size first_page,
  96                                                            Size npages);
  97 extern char *FreePageManagerDump(FreePageManager *fpm);
  98
  99 #endif                                                  /* FREEPAGE_H */