src/runtime/gencgc-internal.h

   1 /*
   2  * Generational Conservative Garbage Collector for SBCL x86
   3  *
   4  * inline functions that gc-common.c needs sight of
   5  */
   6
   7
   8 /*
   9  * This software is part of the SBCL system. See the README file for
  10  * more information.
  11  *
  12  * This software is derived from the CMU CL system, which was
  13  * written at Carnegie Mellon University and released into the
  14  * public domain. The software is in the public domain and is
  15  * provided with absolutely no warranty. See the COPYING and CREDITS
  16  * files for more information.
  17  */
  18
  19 #ifndef _GENCGC_INTERNAL_H_
  20 #define _GENCGC_INTERNAL_H_
  21
  22 #include <limits.h>
  23 #include "gc.h"
  24 #include "gencgc-alloc-region.h"
  25 #include "genesis/code.h"
  26
  27 void gc_free_heap(void);
  28 extern void *page_address(page_index_t);
  29 int gencgc_handle_wp_violation(void *);
  30 \f
  31
  32 #if N_WORD_BITS == 64
  33   // It's more economical to store scan_start_offset using 4 bytes than 8.
  34   // Doing so makes struct page fit in 8 bytes if bytes_used takes 2 bytes.
  35   //   scan_start_offset = 4
  36   //   bytes_used        = 2
  37   //   flags             = 1
  38   //   gen               = 1
  39   // If bytes_used takes 4 bytes, then the above is 10 bytes which is padded to
  40   // 12, which is still an improvement over the 16 that it would have been.
  41 # define CONDENSED_PAGE_TABLE
  42 #endif
  43
  44 #if GENCGC_CARD_BYTES > USHRT_MAX
  45 # if GENCGC_CARD_BYTES > UINT_MAX
  46 #   error "GENCGC_CARD_BYTES unexpectedly large."
  47 # else
  48     typedef unsigned int page_bytes_t;
  49 # endif
  50 #else
  51   typedef unsigned short page_bytes_t;
  52 #endif
  53
  54 /* Note that this structure is also used from Lisp-side in
  55  * src/code/room.lisp, and the Lisp-side structure layout is currently
  56  * not groveled from C code but hardcoded. Any changes to the
  57  * structure layout need to be also made there.
  58  *
  59  * FIXME: We should probably just define this structure in Lisp, and
  60  * output the C version in genesis. -- JES, 2006-12-30.
  61  */
  62 struct page {
  63     /* This is the offset from the first byte of some object in memory
  64      * prior to and no closer than the start of the page to the start
  65      * of the page.  Lower values here are better, 0 is ideal.  This
  66      * is useful for determining where to start when scanning forward
  67      * through a heap page (either for conservative root validation or
  68      * for scavenging).
  69      */
  70 #ifdef CONDENSED_PAGE_TABLE
  71     // The low bit of the offset indicates the scale factor:
  72     // 0 = double-lispwords, 1 = gc cards. Large objects are card-aligned,
  73     // and this representation allows for a 32TB contiguous block using 32K
  74     // card size. Larger allocations will have pages that can't directly
  75     // store the full offset. That has to be dealt with by the accessor.
  76     unsigned int scan_start_offset_;
  77 #else
  78     os_vm_size_t scan_start_offset_;
  79 #endif
  80
  81     /* the number of bytes of this page that are used. This may be less
  82      * than the actual bytes used for pages within the current
  83      * allocation regions. It should be 0 for all unallocated pages (not
  84      * hard to achieve).
  85      * When read, the low bit has to be masked off.
  86      */
  87     page_bytes_t bytes_used_;
  88
  89     unsigned char
  90         /* This is set when the page is write-protected. This should
  91          * always reflect the actual write_protect status of a page.
  92          * (If the page is written into, we catch the exception, make
  93          * the page writable, and clear this flag.) */
  94         write_protected :1,
  95         /* This flag is set when the above write_protected flag is
  96          * cleared by the SIGBUS handler (or SIGSEGV handler, for some
  97          * OSes). This is useful for re-scavenging pages that are
  98          * written during a GC. */
  99         write_protected_cleared :1,
 100         /*  000 free
 101          *  ?01 boxed data
 102          *  ?10 unboxed data
 103          *  ?11 code
 104          *  1?? open region
 105          *
 106          * Constants for this field are defined in gc-internal.h, the
 107          * xxx_PAGE_FLAG definitions.
 108          *
 109          * If the page is free the following slots are invalid, except
 110          * for the bytes_used which must be zero. */
 111         allocated :3,
 112         /* If this page should not be moved during a GC then this flag
 113          * is set. It's only valid during a GC for allocated pages. */
 114         dont_move :1,
 115         /* If this page is not a large object page and contains
 116          * any objects which are pinned */
 117         has_pin_map :1,
 118         /* If the page is part of a large object then this flag is
 119          * set. No other objects should be allocated to these pages.
 120          * This is only valid when the page is allocated. */
 121         large_object :1;
 122
 123     /* the generation that this page belongs to. This should be valid
 124      * for all pages that may have objects allocated, even current
 125      * allocation region pages - this allows the space of an object to
 126      * be easily determined. */
 127     generation_index_t gen;
 128 };
 129 extern struct page *page_table;
 130
 131 #ifndef CONDENSED_PAGE_TABLE
 132
 133 // 32-bit doesn't need magic to reduce the size of scan_start_offset.
 134 #define set_page_scan_start_offset(index,val) \
 135   page_table[index].scan_start_offset_ = val
 136 #define page_scan_start_offset(index) page_table[index].scan_start_offset_
 137
 138 #else
 139
 140 /// A "condensed" offset reduces page table size, which improves scan locality.
 141 /// As stored, the offset is scaled down either by card size or double-lispwords.
 142 /// If the offset is the maximum, then we must check if the page pointed to by
 143 /// that offset is actually the start of a region, and retry if not.
 144 /// For debugging the iterative algorithm it helps to use a max value
 145 /// that is less than UINT_MAX to get a pass/fail more quickly.
 146
 147 //#define SCAN_START_OFS_MAX 0x3fff
 148 #define SCAN_START_OFS_MAX UINT_MAX
 149
 150 #define page_scan_start_offset(index) \
 151   (page_table[index].scan_start_offset_ != SCAN_START_OFS_MAX \
 152     ? (os_vm_size_t)(page_table[index].scan_start_offset_ & ~1) \
 153        << ((page_table[index].scan_start_offset_ & 1)?(GENCGC_CARD_SHIFT-1):WORD_SHIFT) \
 154     : scan_start_offset_iterated(index))
 155
 156 static os_vm_size_t __attribute__((unused))
 157 scan_start_offset_iterated(page_index_t index)
 158 {
 159     // The low bit of the MAX is the 'scale' bit. The max pages we can look
 160     // backwards is therefore the max shifted right by 1 bit.
 161     page_index_t tot_offset_in_pages = 0;
 162     unsigned int offset;
 163     do {
 164         page_index_t lookback_page = index - tot_offset_in_pages;
 165         offset = page_table[lookback_page].scan_start_offset_;
 166         tot_offset_in_pages += offset >> 1;
 167     } while (offset == SCAN_START_OFS_MAX);
 168     return (os_vm_size_t)tot_offset_in_pages << GENCGC_CARD_SHIFT;
 169 }
 170
 171 #define set_page_scan_start_offset(index, ofs) \
 172   { unsigned int lsb_ = ((ofs) & (GENCGC_CARD_BYTES-1)) == 0; \
 173     os_vm_size_t scaled_ = ((ofs) >> (lsb_ ? GENCGC_CARD_SHIFT-1 : WORD_SHIFT)) | lsb_; \
 174     if (scaled_ > SCAN_START_OFS_MAX) gc_assert(lsb_ == 1); \
 175     page_table[index].scan_start_offset_ = \
 176         scaled_ > SCAN_START_OFS_MAX ? SCAN_START_OFS_MAX : scaled_; }
 177
 178 #endif
 179
 180 /// There is some additional cleverness that could potentially be had -
 181 /// the "need_to_zero" bit (a/k/a "page dirty") is obviously 1 if the page
 182 /// contains objects. Only for an empty page must we distinguish between pages
 183 /// not needing be zero-filled before next use and those which must be.
 184 /// Thus, masking off the dirty bit could be avoided by not storing it for
 185 /// any in-use page. But since that's not what we do - we set the bit to 1
 186 /// as soon as a page is used - we do have to mask off the bit.
 187 #define page_bytes_used(index) (page_table[index].bytes_used_ & ~1)
 188 #define page_need_to_zero(index) (page_table[index].bytes_used_ & 1)
 189 #define set_page_bytes_used(index,val) \
 190   page_table[index].bytes_used_ = (val) | page_need_to_zero(index)
 191 #define set_page_need_to_zero(index,val) \
 192   page_table[index].bytes_used_ = page_bytes_used(index) | val
 193
 194 /* values for the page.allocated field */
 195
 196 \f
 197 extern page_index_t page_table_pages;
 198
 199 \f
 200 /* forward declarations */
 201 #ifdef LISP_FEATURE_X86
 202 void sniff_code_object(struct code *code, os_vm_size_t displacement);
 203 void gencgc_apply_code_fixups(struct code *old_code, struct code *new_code);
 204 #endif
 205
 206 sword_t update_dynamic_space_free_pointer(void);
 207 void gc_alloc_update_page_tables(int page_type_flag, struct alloc_region *alloc_region);
 208 void gc_alloc_update_all_page_tables(int);
 209 void gc_set_region_empty(struct alloc_region *region);
 210
 211 /*
 212  * predicates
 213  */
 214
 215 /* Find the page index within the page_table for the given
 216  * address. Return -1 on failure. */
 217 static inline page_index_t
 218 find_page_index(void *addr)
 219 {
 220     if (addr >= (void*)DYNAMIC_SPACE_START) {
 221         page_index_t index = ((pointer_sized_uint_t)addr -
 222                               (pointer_sized_uint_t)DYNAMIC_SPACE_START) / GENCGC_CARD_BYTES;
 223         if (index < page_table_pages)
 224             return (index);
 225     }
 226     return (-1);
 227 }
 228
 229 static const int n_dwords_in_card = GENCGC_CARD_BYTES / N_WORD_BYTES / 2;
 230 extern uword_t *page_table_pinned_dwords;
 231
 232 static inline boolean pinned_p(lispobj obj, page_index_t page)
 233 {
 234     if (!page_table[page].has_pin_map) return 0;
 235     int dword_num = (obj & (GENCGC_CARD_BYTES-1)) >> (1+WORD_SHIFT);
 236     uword_t *bits = &page_table_pinned_dwords[page * (n_dwords_in_card/N_WORD_BITS)];
 237     return (bits[dword_num / N_WORD_BITS] >> (dword_num % N_WORD_BITS)) & 1;
 238 }
 239
 240 // Return true only if 'obj' must be *physically* transported to survive gc.
 241 // Return false if obj is in the immobile space regardless of its generation.
 242 // Pretend pinned objects are not in oldspace so that they don't get moved.
 243 // Any lowtag bits on 'obj' are ignored.
 244 static boolean __attribute__((unused))
 245 from_space_p(lispobj obj)
 246 {
 247     page_index_t page_index = find_page_index((void*)obj);
 248     return page_index >= 0
 249         && page_table[page_index].gen == from_space
 250         && !pinned_p(obj, page_index);
 251 }
 252 static inline boolean
 253 new_space_p(lispobj obj)
 254 {
 255     page_index_t page_index = find_page_index((void*)obj);
 256     return page_index >= 0 && page_table[page_index].gen == new_space;
 257 }
 258
 259 extern page_index_t last_free_page;
 260 extern boolean gencgc_partial_pickup;
 261
 262 #endif