1 /* "Bag-of-pages" garbage collector for the GNU compiler.
2 Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
4 This file is part of GNU CC.
6 GNU CC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GNU CC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU CC; see the file COPYING. If not, write to
18 the Free Software Foundation, 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
32 #ifdef HAVE_MMAP_ANYWHERE
40 #if !defined (MAP_ANONYMOUS) && defined (MAP_ANON)
41 #define MAP_ANONYMOUS MAP_ANON
46 This garbage-collecting allocator allocates objects on one of a set
47 of pages. Each page can allocate objects of a single size only;
48 available sizes are powers of two starting at four bytes. The size
49 of an allocation request is rounded up to the next power of two
50 (`order'), and satisfied from the appropriate page.
52 Each page is recorded in a page-entry, which also maintains an
53 in-use bitmap of object positions on the page. This allows the
54 allocation state of a particular object to be flipped without
55 touching the page itself.
57 Each page-entry also has a context depth, which is used to track
58 pushing and popping of allocation contexts. Only objects allocated
59 in the current (highest-numbered) context may be collected.
61 Page entries are arranged in an array of singly-linked lists. The
62 array is indexed by the allocation size, in bits, of the pages on
63 it; i.e. all pages on a list allocate objects of the same size.
64 Pages are ordered on the list such that all non-full pages precede
65 all full pages, with non-full pages arranged in order of decreasing
68 Empty pages (of all orders) are kept on a single page cache list,
69 and are considered first when new pages are required; they are
70 deallocated at the start of the next collection if they haven't
71 been recycled by then. */
74 /* Define GGC_POISON to poison memory marked unused by the collector. */
77 /* Define GGC_ALWAYS_COLLECT to perform collection every time
78 ggc_collect is invoked. Otherwise, collection is performed only
79 when a significant amount of memory has been allocated since the
81 #undef GGC_ALWAYS_COLLECT
83 #ifdef ENABLE_GC_CHECKING
86 #ifdef ENABLE_GC_ALWAYS_COLLECT
87 #define GGC_ALWAYS_COLLECT
90 /* Define GGC_DEBUG_LEVEL to print debugging information.
91 0: No debugging output.
92 1: GC statistics only.
93 2: Page-entry allocations/deallocations as well.
94 3: Object allocations as well.
95 4: Object marks as well. */
96 #define GGC_DEBUG_LEVEL (0)
98 #ifndef HOST_BITS_PER_PTR
99 #define HOST_BITS_PER_PTR HOST_BITS_PER_LONG
103 /* A two-level tree is used to look up the page-entry for a given
104 pointer. Two chunks of the pointer's bits are extracted to index
105 the first and second levels of the tree, as follows:
109 msb +----------------+----+------+------+ lsb
115 The bottommost HOST_PAGE_SIZE_BITS are ignored, since page-entry
116 pages are aligned on system page boundaries. The next most
117 significant PAGE_L2_BITS and PAGE_L1_BITS are the second and first
118 index values in the lookup table, respectively.
120 For 32-bit architectures and the settings below, there are no
121 leftover bits. For architectures with wider pointers, the lookup
122 tree points to a list of pages, which must be scanned to find the
125 #define PAGE_L1_BITS (8)
126 #define PAGE_L2_BITS (32 - PAGE_L1_BITS - G.lg_pagesize)
127 #define PAGE_L1_SIZE ((size_t) 1 << PAGE_L1_BITS)
128 #define PAGE_L2_SIZE ((size_t) 1 << PAGE_L2_BITS)
130 #define LOOKUP_L1(p) \
131 (((size_t) (p) >> (32 - PAGE_L1_BITS)) & ((1 << PAGE_L1_BITS) - 1))
133 #define LOOKUP_L2(p) \
134 (((size_t) (p) >> G.lg_pagesize) & ((1 << PAGE_L2_BITS) - 1))
136 /* The number of objects per allocation page, for objects on a page of
137 the indicated ORDER. */
138 #define OBJECTS_PER_PAGE(ORDER) objects_per_page_table[ORDER]
140 /* The size of an object on a page of the indicated ORDER. */
141 #define OBJECT_SIZE(ORDER) object_size_table[ORDER]
143 /* The number of extra orders, not corresponding to power-of-two sized
146 #define NUM_EXTRA_ORDERS \
147 (sizeof (extra_order_size_table) / sizeof (extra_order_size_table[0]))
149 /* The Ith entry is the maximum size of an object to be stored in the
150 Ith extra order. Adding a new entry to this array is the *only*
151 thing you need to do to add a new special allocation size. */
153 static const size_t extra_order_size_table[] = {
154 sizeof (struct tree_decl),
155 sizeof (struct tree_list)
158 /* The total number of orders. */
160 #define NUM_ORDERS (HOST_BITS_PER_PTR + NUM_EXTRA_ORDERS)
162 /* The Ith entry is the number of objects on a page or order I. */
164 static unsigned objects_per_page_table[NUM_ORDERS];
166 /* The Ith entry is the size of an object on a page of order I. */
168 static size_t object_size_table[NUM_ORDERS];
170 /* A page_entry records the status of an allocation page. This
171 structure is dynamically sized to fit the bitmap in_use_p. */
172 typedef struct page_entry
174 /* The next page-entry with objects of the same size, or NULL if
175 this is the last page-entry. */
176 struct page_entry *next;
178 /* The number of bytes allocated. (This will always be a multiple
179 of the host system page size.) */
182 /* The address at which the memory is allocated. */
185 /* Saved in-use bit vector for pages that aren't in the topmost
186 context during collection. */
187 unsigned long *save_in_use_p;
189 /* Context depth of this page. */
190 unsigned short context_depth;
192 /* The number of free objects remaining on this page. */
193 unsigned short num_free_objects;
195 /* A likely candidate for the bit position of a free object for the
196 next allocation from this page. */
197 unsigned short next_bit_hint;
199 /* The lg of size of objects allocated from this page. */
202 /* A bit vector indicating whether or not objects are in use. The
203 Nth bit is one if the Nth object on this page is allocated. This
204 array is dynamically sized. */
205 unsigned long in_use_p[1];
209 #if HOST_BITS_PER_PTR <= 32
211 /* On 32-bit hosts, we use a two level page table, as pictured above. */
212 typedef page_entry **page_table[PAGE_L1_SIZE];
216 /* On 64-bit hosts, we use the same two level page tables plus a linked
217 list that disambiguates the top 32-bits. There will almost always be
218 exactly one entry in the list. */
219 typedef struct page_table_chain
221 struct page_table_chain *next;
223 page_entry **table[PAGE_L1_SIZE];
228 /* The rest of the global variables. */
229 static struct globals
231 /* The Nth element in this array is a page with objects of size 2^N.
232 If there are any pages with free objects, they will be at the
233 head of the list. NULL if there are no page-entries for this
235 page_entry *pages[NUM_ORDERS];
237 /* The Nth element in this array is the last page with objects of
238 size 2^N. NULL if there are no page-entries for this object
240 page_entry *page_tails[NUM_ORDERS];
242 /* Lookup table for associating allocation pages with object addresses. */
245 /* The system's page size. */
249 /* Bytes currently allocated. */
252 /* Bytes currently allocated at the end of the last collection. */
253 size_t allocated_last_gc;
255 /* Total amount of memory mapped. */
258 /* The current depth in the context stack. */
259 unsigned short context_depth;
261 /* A file descriptor open to /dev/zero for reading. */
262 #if defined (HAVE_MMAP_ANYWHERE) && !defined(MAP_ANONYMOUS)
266 /* A cache of free system pages. */
267 page_entry *free_pages;
269 /* The file descriptor for debugging output. */
273 /* The size in bytes required to maintain a bitmap for the objects
275 #define BITMAP_SIZE(Num_objects) \
276 (CEIL ((Num_objects), HOST_BITS_PER_LONG) * sizeof(long))
278 /* Skip garbage collection if the current allocation is not at least
279 this factor times the allocation at the end of the last collection.
280 In other words, total allocation must expand by (this factor minus
281 one) before collection is performed. */
282 #define GGC_MIN_EXPAND_FOR_GC (1.3)
284 /* Bound `allocated_last_gc' to 4MB, to prevent the memory expansion
285 test from triggering too often when the heap is small. */
286 #define GGC_MIN_LAST_ALLOCATED (4 * 1024 * 1024)
288 /* Allocate pages in chunks of this size, to throttle calls to mmap.
289 The first page is used, the rest go onto the free list. */
290 #define GGC_QUIRE_SIZE 16
293 static int ggc_allocated_p PARAMS ((const void *));
294 static page_entry *lookup_page_table_entry PARAMS ((const void *));
295 static void set_page_table_entry PARAMS ((void *, page_entry *));
296 static char *alloc_anon PARAMS ((char *, size_t));
297 static struct page_entry * alloc_page PARAMS ((unsigned));
298 static void free_page PARAMS ((struct page_entry *));
299 static void release_pages PARAMS ((void));
300 static void clear_marks PARAMS ((void));
301 static void sweep_pages PARAMS ((void));
302 static void ggc_recalculate_in_use_p PARAMS ((page_entry *));
305 static void poison_pages PARAMS ((void));
308 void debug_print_page_list PARAMS ((int));
310 /* Returns non-zero if P was allocated in GC'able memory. */
319 #if HOST_BITS_PER_PTR <= 32
322 page_table table = G.lookup;
323 size_t high_bits = (size_t) p & ~ (size_t) 0xffffffff;
328 if (table->high_bits == high_bits)
332 base = &table->table[0];
335 /* Extract the level 1 and 2 indicies. */
339 return base[L1] && base[L1][L2];
342 /* Traverse the page table and find the entry for a page.
343 Die (probably) if the object wasn't allocated via GC. */
345 static inline page_entry *
346 lookup_page_table_entry(p)
352 #if HOST_BITS_PER_PTR <= 32
355 page_table table = G.lookup;
356 size_t high_bits = (size_t) p & ~ (size_t) 0xffffffff;
357 while (table->high_bits != high_bits)
359 base = &table->table[0];
362 /* Extract the level 1 and 2 indicies. */
369 /* Set the page table entry for a page. */
372 set_page_table_entry(p, entry)
379 #if HOST_BITS_PER_PTR <= 32
383 size_t high_bits = (size_t) p & ~ (size_t) 0xffffffff;
384 for (table = G.lookup; table; table = table->next)
385 if (table->high_bits == high_bits)
388 /* Not found -- allocate a new table. */
389 table = (page_table) xcalloc (1, sizeof(*table));
390 table->next = G.lookup;
391 table->high_bits = high_bits;
394 base = &table->table[0];
397 /* Extract the level 1 and 2 indicies. */
401 if (base[L1] == NULL)
402 base[L1] = (page_entry **) xcalloc (PAGE_L2_SIZE, sizeof (page_entry *));
404 base[L1][L2] = entry;
407 /* Prints the page-entry for object size ORDER, for debugging. */
410 debug_print_page_list (order)
414 printf ("Head=%p, Tail=%p:\n", (PTR) G.pages[order],
415 (PTR) G.page_tails[order]);
419 printf ("%p(%1d|%3d) -> ", (PTR) p, p->context_depth,
420 p->num_free_objects);
427 /* Allocate SIZE bytes of anonymous memory, preferably near PREF,
431 alloc_anon (pref, size)
432 char *pref ATTRIBUTE_UNUSED;
437 #ifdef HAVE_MMAP_ANYWHERE
439 page = (char *) mmap (pref, size, PROT_READ | PROT_WRITE,
440 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
442 page = (char *) mmap (pref, size, PROT_READ | PROT_WRITE,
443 MAP_PRIVATE, G.dev_zero_fd, 0);
445 if (page == (char *) MAP_FAILED)
447 fputs ("Virtual memory exhausted!\n", stderr);
452 page = (char *) valloc (size);
455 fputs ("Virtual memory exhausted!\n", stderr);
458 #endif /* HAVE_VALLOC */
459 #endif /* HAVE_MMAP_ANYWHERE */
461 /* Remember that we allocated this memory. */
462 G.bytes_mapped += size;
467 /* Allocate a new page for allocating objects of size 2^ORDER,
468 and return an entry for it. The entry is not added to the
469 appropriate page_table list. */
471 static inline struct page_entry *
475 struct page_entry *entry, *p, **pp;
479 size_t page_entry_size;
482 num_objects = OBJECTS_PER_PAGE (order);
483 bitmap_size = BITMAP_SIZE (num_objects + 1);
484 page_entry_size = sizeof (page_entry) - sizeof (long) + bitmap_size;
485 entry_size = num_objects * OBJECT_SIZE (order);
490 /* Check the list of free pages for one we can use. */
491 for (pp = &G.free_pages, p = *pp; p ; pp = &p->next, p = *pp)
492 if (p->bytes == entry_size)
497 /* Recycle the allocated memory from this page ... */
500 /* ... and, if possible, the page entry itself. */
501 if (p->order == order)
504 memset (entry, 0, page_entry_size);
509 #ifdef HAVE_MMAP_ANYWHERE
510 else if (entry_size == G.pagesize)
512 /* We want just one page. Allocate a bunch of them and put the
513 extras on the freelist. (Can only do this optimization with
514 mmap for backing store.) */
515 struct page_entry *e, *f = G.free_pages;
518 page = alloc_anon (NULL, entry_size * GGC_QUIRE_SIZE);
519 /* This loop counts down so that the chain will be in ascending
521 for (i = GGC_QUIRE_SIZE - 1; i >= 1; i--)
523 e = (struct page_entry *) xcalloc (1, sizeof (struct page_entry));
524 e->bytes = entry_size;
525 e->page = page + i*entry_size;
533 page = alloc_anon (NULL, entry_size);
536 entry = (struct page_entry *) xcalloc (1, page_entry_size);
538 entry->bytes = entry_size;
540 entry->context_depth = G.context_depth;
541 entry->order = order;
542 entry->num_free_objects = num_objects;
543 entry->next_bit_hint = 1;
545 /* Set the one-past-the-end in-use bit. This acts as a sentry as we
546 increment the hint. */
547 entry->in_use_p[num_objects / HOST_BITS_PER_LONG]
548 = (unsigned long) 1 << (num_objects % HOST_BITS_PER_LONG);
550 set_page_table_entry (page, entry);
552 if (GGC_DEBUG_LEVEL >= 2)
553 fprintf (G.debug_file,
554 "Allocating page at %p, object size=%d, data %p-%p\n",
555 (PTR) entry, OBJECT_SIZE (order), page, page + entry_size - 1);
560 /* For a page that is no longer needed, put it on the free page list. */
566 if (GGC_DEBUG_LEVEL >= 2)
567 fprintf (G.debug_file,
568 "Deallocating page at %p, data %p-%p\n", (PTR) entry,
569 entry->page, entry->page + entry->bytes - 1);
571 set_page_table_entry (entry->page, NULL);
573 entry->next = G.free_pages;
574 G.free_pages = entry;
577 /* Release the free page cache to the system. */
582 page_entry *p, *next;
584 #ifdef HAVE_MMAP_ANYWHERE
588 /* Gather up adjacent pages so they are unmapped together. */
599 while (p && p->page == start + len)
608 G.bytes_mapped -= len;
613 for (p = G.free_pages; p; p = next)
617 G.bytes_mapped -= p->bytes;
620 #endif /* HAVE_VALLOC */
621 #endif /* HAVE_MMAP_ANYWHERE */
626 /* This table provides a fast way to determine ceil(log_2(size)) for
627 allocation requests. The minimum allocation size is four bytes. */
629 static unsigned char size_lookup[257] =
631 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4,
632 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
633 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
634 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
635 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
636 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
637 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
638 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
639 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
640 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
641 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
642 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
643 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
644 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
645 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
646 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
650 /* Allocate a chunk of memory of SIZE bytes. If ZERO is non-zero, the
651 memory is zeroed; otherwise, its contents are undefined. */
657 unsigned order, word, bit, object_offset;
658 struct page_entry *entry;
662 order = size_lookup[size];
666 while (size > OBJECT_SIZE (order))
670 /* If there are non-full pages for this size allocation, they are at
671 the head of the list. */
672 entry = G.pages[order];
674 /* If there is no page for this object size, or all pages in this
675 context are full, allocate a new page. */
676 if (entry == NULL || entry->num_free_objects == 0)
678 struct page_entry *new_entry;
679 new_entry = alloc_page (order);
681 /* If this is the only entry, it's also the tail. */
683 G.page_tails[order] = new_entry;
685 /* Put new pages at the head of the page list. */
686 new_entry->next = entry;
688 G.pages[order] = new_entry;
690 /* For a new page, we know the word and bit positions (in the
691 in_use bitmap) of the first available object -- they're zero. */
692 new_entry->next_bit_hint = 1;
699 /* First try to use the hint left from the previous allocation
700 to locate a clear bit in the in-use bitmap. We've made sure
701 that the one-past-the-end bit is always set, so if the hint
702 has run over, this test will fail. */
703 unsigned hint = entry->next_bit_hint;
704 word = hint / HOST_BITS_PER_LONG;
705 bit = hint % HOST_BITS_PER_LONG;
707 /* If the hint didn't work, scan the bitmap from the beginning. */
708 if ((entry->in_use_p[word] >> bit) & 1)
711 while (~entry->in_use_p[word] == 0)
713 while ((entry->in_use_p[word] >> bit) & 1)
715 hint = word * HOST_BITS_PER_LONG + bit;
718 /* Next time, try the next bit. */
719 entry->next_bit_hint = hint + 1;
721 object_offset = hint * OBJECT_SIZE (order);
724 /* Set the in-use bit. */
725 entry->in_use_p[word] |= ((unsigned long) 1 << bit);
727 /* Keep a running total of the number of free objects. If this page
728 fills up, we may have to move it to the end of the list if the
729 next page isn't full. If the next page is full, all subsequent
730 pages are full, so there's no need to move it. */
731 if (--entry->num_free_objects == 0
732 && entry->next != NULL
733 && entry->next->num_free_objects > 0)
735 G.pages[order] = entry->next;
737 G.page_tails[order]->next = entry;
738 G.page_tails[order] = entry;
741 /* Calculate the object's address. */
742 result = entry->page + object_offset;
745 /* `Poison' the entire allocated object, including any padding at
747 memset (result, 0xaf, OBJECT_SIZE (order));
750 /* Keep track of how many bytes are being allocated. This
751 information is used in deciding when to collect. */
752 G.allocated += OBJECT_SIZE (order);
754 if (GGC_DEBUG_LEVEL >= 3)
755 fprintf (G.debug_file,
756 "Allocating object, requested size=%d, actual=%d at %p on %p\n",
757 (int) size, OBJECT_SIZE (order), result, (PTR) entry);
762 /* If P is not marked, marks it and return false. Otherwise return true.
763 P must have been allocated by the GC allocator; it mustn't point to
764 static objects, stack variables, or memory allocated with malloc. */
774 /* Look up the page on which the object is alloced. If the object
775 wasn't allocated by the collector, we'll probably die. */
776 entry = lookup_page_table_entry (p);
777 #ifdef ENABLE_CHECKING
782 /* Calculate the index of the object on the page; this is its bit
783 position in the in_use_p bitmap. */
784 bit = (((const char *) p) - entry->page) / OBJECT_SIZE (entry->order);
785 word = bit / HOST_BITS_PER_LONG;
786 mask = (unsigned long) 1 << (bit % HOST_BITS_PER_LONG);
788 /* If the bit was previously set, skip it. */
789 if (entry->in_use_p[word] & mask)
792 /* Otherwise set it, and decrement the free object count. */
793 entry->in_use_p[word] |= mask;
794 entry->num_free_objects -= 1;
796 if (GGC_DEBUG_LEVEL >= 4)
797 fprintf (G.debug_file, "Marking %p\n", p);
802 /* Mark P, but check first that it was allocated by the collector. */
805 ggc_mark_if_gcable (p)
808 if (p && ggc_allocated_p (p))
812 /* Return the size of the gc-able object P. */
818 page_entry *pe = lookup_page_table_entry (p);
819 return OBJECT_SIZE (pe->order);
822 /* Initialize the ggc-mmap allocator. */
829 G.pagesize = getpagesize();
830 G.lg_pagesize = exact_log2 (G.pagesize);
832 #if defined (HAVE_MMAP_ANYWHERE) && !defined(MAP_ANONYMOUS)
833 G.dev_zero_fd = open ("/dev/zero", O_RDONLY);
834 if (G.dev_zero_fd == -1)
839 G.debug_file = fopen ("ggc-mmap.debug", "w");
841 G.debug_file = stdout;
844 G.allocated_last_gc = GGC_MIN_LAST_ALLOCATED;
846 #ifdef HAVE_MMAP_ANYWHERE
847 /* StunOS has an amazing off-by-one error for the first mmap allocation
848 after fiddling with RLIMIT_STACK. The result, as hard as it is to
849 believe, is an unaligned page allocation, which would cause us to
850 hork badly if we tried to use it. */
852 char *p = alloc_anon (NULL, G.pagesize);
853 if ((size_t)p & (G.pagesize - 1))
855 /* How losing. Discard this one and try another. If we still
856 can't get something useful, give up. */
858 p = alloc_anon (NULL, G.pagesize);
859 if ((size_t)p & (G.pagesize - 1))
862 munmap (p, G.pagesize);
866 /* Initialize the object size table. */
867 for (order = 0; order < HOST_BITS_PER_PTR; ++order)
868 object_size_table[order] = (size_t) 1 << order;
869 for (order = HOST_BITS_PER_PTR; order < NUM_ORDERS; ++order)
870 object_size_table[order] =
871 extra_order_size_table[order - HOST_BITS_PER_PTR];
873 /* Initialize the objects-per-page table. */
874 for (order = 0; order < NUM_ORDERS; ++order)
876 objects_per_page_table[order] = G.pagesize / OBJECT_SIZE (order);
877 if (objects_per_page_table[order] == 0)
878 objects_per_page_table[order] = 1;
881 /* Reset the size_lookup array to put appropriately sized objects in
882 the special orders. All objects bigger than the previous power
883 of two, but no greater than the special size, should go in the
885 for (order = HOST_BITS_PER_PTR; order < NUM_ORDERS; ++order)
890 o = size_lookup[OBJECT_SIZE (order)];
891 for (i = OBJECT_SIZE (order); size_lookup [i] == o; --i)
892 size_lookup[i] = order;
896 /* Increment the `GC context'. Objects allocated in an outer context
897 are never freed, eliminating the need to register their roots. */
905 if (G.context_depth == 0)
909 /* Merge the SAVE_IN_USE_P and IN_USE_P arrays in P so that IN_USE_P
910 reflects reality. Recalculate NUM_FREE_OBJECTS as well. */
913 ggc_recalculate_in_use_p (p)
919 /* Because the past-the-end bit in in_use_p is always set, we
920 pretend there is one additional object. */
921 num_objects = OBJECTS_PER_PAGE (p->order) + 1;
923 /* Reset the free object count. */
924 p->num_free_objects = num_objects;
926 /* Combine the IN_USE_P and SAVE_IN_USE_P arrays. */
928 i < CEIL (BITMAP_SIZE (num_objects),
929 sizeof (*p->in_use_p));
934 /* Something is in use if it is marked, or if it was in use in a
935 context further down the context stack. */
936 p->in_use_p[i] |= p->save_in_use_p[i];
938 /* Decrement the free object count for every object allocated. */
939 for (j = p->in_use_p[i]; j; j >>= 1)
940 p->num_free_objects -= (j & 1);
943 if (p->num_free_objects >= num_objects)
947 /* Decrement the `GC context'. All objects allocated since the
948 previous ggc_push_context are migrated to the outer context. */
953 unsigned order, depth;
955 depth = --G.context_depth;
957 /* Any remaining pages in the popped context are lowered to the new
958 current context; i.e. objects allocated in the popped context and
959 left over are imported into the previous context. */
960 for (order = 2; order < NUM_ORDERS; order++)
964 for (p = G.pages[order]; p != NULL; p = p->next)
966 if (p->context_depth > depth)
967 p->context_depth = depth;
969 /* If this page is now in the topmost context, and we'd
970 saved its allocation state, restore it. */
971 else if (p->context_depth == depth && p->save_in_use_p)
973 ggc_recalculate_in_use_p (p);
974 free (p->save_in_use_p);
975 p->save_in_use_p = 0;
981 /* Unmark all objects. */
988 for (order = 2; order < NUM_ORDERS; order++)
990 size_t num_objects = OBJECTS_PER_PAGE (order);
991 size_t bitmap_size = BITMAP_SIZE (num_objects + 1);
994 for (p = G.pages[order]; p != NULL; p = p->next)
996 #ifdef ENABLE_CHECKING
997 /* The data should be page-aligned. */
998 if ((size_t) p->page & (G.pagesize - 1))
1002 /* Pages that aren't in the topmost context are not collected;
1003 nevertheless, we need their in-use bit vectors to store GC
1004 marks. So, back them up first. */
1005 if (p->context_depth < G.context_depth)
1007 if (! p->save_in_use_p)
1008 p->save_in_use_p = xmalloc (bitmap_size);
1009 memcpy (p->save_in_use_p, p->in_use_p, bitmap_size);
1012 /* Reset reset the number of free objects and clear the
1013 in-use bits. These will be adjusted by mark_obj. */
1014 p->num_free_objects = num_objects;
1015 memset (p->in_use_p, 0, bitmap_size);
1017 /* Make sure the one-past-the-end bit is always set. */
1018 p->in_use_p[num_objects / HOST_BITS_PER_LONG]
1019 = ((unsigned long) 1 << (num_objects % HOST_BITS_PER_LONG));
1024 /* Free all empty pages. Partially empty pages need no attention
1025 because the `mark' bit doubles as an `unused' bit. */
1032 for (order = 2; order < NUM_ORDERS; order++)
1034 /* The last page-entry to consider, regardless of entries
1035 placed at the end of the list. */
1036 page_entry * const last = G.page_tails[order];
1038 size_t num_objects = OBJECTS_PER_PAGE (order);
1039 size_t live_objects;
1040 page_entry *p, *previous;
1050 page_entry *next = p->next;
1052 /* Loop until all entries have been examined. */
1055 /* Add all live objects on this page to the count of
1056 allocated memory. */
1057 live_objects = num_objects - p->num_free_objects;
1059 G.allocated += OBJECT_SIZE (order) * live_objects;
1061 /* Only objects on pages in the topmost context should get
1063 if (p->context_depth < G.context_depth)
1066 /* Remove the page if it's empty. */
1067 else if (live_objects == 0)
1070 G.pages[order] = next;
1072 previous->next = next;
1074 /* Are we removing the last element? */
1075 if (p == G.page_tails[order])
1076 G.page_tails[order] = previous;
1081 /* If the page is full, move it to the end. */
1082 else if (p->num_free_objects == 0)
1084 /* Don't move it if it's already at the end. */
1085 if (p != G.page_tails[order])
1087 /* Move p to the end of the list. */
1089 G.page_tails[order]->next = p;
1091 /* Update the tail pointer... */
1092 G.page_tails[order] = p;
1094 /* ... and the head pointer, if necessary. */
1096 G.pages[order] = next;
1098 previous->next = next;
1103 /* If we've fallen through to here, it's a page in the
1104 topmost context that is neither full nor empty. Such a
1105 page must precede pages at lesser context depth in the
1106 list, so move it to the head. */
1107 else if (p != G.pages[order])
1109 previous->next = p->next;
1110 p->next = G.pages[order];
1112 /* Are we moving the last element? */
1113 if (G.page_tails[order] == p)
1114 G.page_tails[order] = previous;
1123 /* Now, restore the in_use_p vectors for any pages from contexts
1124 other than the current one. */
1125 for (p = G.pages[order]; p; p = p->next)
1126 if (p->context_depth != G.context_depth)
1127 ggc_recalculate_in_use_p (p);
1132 /* Clobber all free objects. */
1139 for (order = 2; order < NUM_ORDERS; order++)
1141 size_t num_objects = OBJECTS_PER_PAGE (order);
1142 size_t size = OBJECT_SIZE (order);
1145 for (p = G.pages[order]; p != NULL; p = p->next)
1149 if (p->context_depth != G.context_depth)
1150 /* Since we don't do any collection for pages in pushed
1151 contexts, there's no need to do any poisoning. And
1152 besides, the IN_USE_P array isn't valid until we pop
1156 for (i = 0; i < num_objects; i++)
1159 word = i / HOST_BITS_PER_LONG;
1160 bit = i % HOST_BITS_PER_LONG;
1161 if (((p->in_use_p[word] >> bit) & 1) == 0)
1162 memset (p->page + i * size, 0xa5, size);
1169 /* Top level mark-and-sweep routine. */
1174 /* Avoid frequent unnecessary work by skipping collection if the
1175 total allocations haven't expanded much since the last
1177 #ifndef GGC_ALWAYS_COLLECT
1178 if (G.allocated < GGC_MIN_EXPAND_FOR_GC * G.allocated_last_gc)
1182 timevar_push (TV_GC);
1184 fprintf (stderr, " {GC %luk -> ", (unsigned long) G.allocated / 1024);
1186 /* Zero the total allocated bytes. This will be recalculated in the
1190 /* Release the pages we freed the last time we collected, but didn't
1191 reuse in the interim. */
1203 G.allocated_last_gc = G.allocated;
1204 if (G.allocated_last_gc < GGC_MIN_LAST_ALLOCATED)
1205 G.allocated_last_gc = GGC_MIN_LAST_ALLOCATED;
1207 timevar_pop (TV_GC);
1210 fprintf (stderr, "%luk}", (unsigned long) G.allocated / 1024);
1213 /* Print allocation statistics. */
1214 #define SCALE(x) ((unsigned long) ((x) < 1024*10 \
1216 : ((x) < 1024*1024*10 \
1218 : (x) / (1024*1024))))
1219 #define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
1222 ggc_print_statistics ()
1224 struct ggc_statistics stats;
1226 size_t total_overhead = 0;
1228 /* Clear the statistics. */
1229 memset (&stats, 0, sizeof (stats));
1231 /* Make sure collection will really occur. */
1232 G.allocated_last_gc = 0;
1234 /* Collect and print the statistics common across collectors. */
1235 ggc_print_common_statistics (stderr, &stats);
1237 /* Release free pages so that we will not count the bytes allocated
1238 there as part of the total allocated memory. */
1241 /* Collect some information about the various sizes of
1243 fprintf (stderr, "\n%-5s %10s %10s %10s\n",
1244 "Log", "Allocated", "Used", "Overhead");
1245 for (i = 0; i < NUM_ORDERS; ++i)
1252 /* Skip empty entries. */
1256 overhead = allocated = in_use = 0;
1258 /* Figure out the total number of bytes allocated for objects of
1259 this size, and how many of them are actually in use. Also figure
1260 out how much memory the page table is using. */
1261 for (p = G.pages[i]; p; p = p->next)
1263 allocated += p->bytes;
1265 (OBJECTS_PER_PAGE (i) - p->num_free_objects) * OBJECT_SIZE (i);
1267 overhead += (sizeof (page_entry) - sizeof (long)
1268 + BITMAP_SIZE (OBJECTS_PER_PAGE (i) + 1));
1270 fprintf (stderr, "%-5d %10ld%c %10ld%c %10ld%c\n", i,
1271 SCALE (allocated), LABEL (allocated),
1272 SCALE (in_use), LABEL (in_use),
1273 SCALE (overhead), LABEL (overhead));
1274 total_overhead += overhead;
1276 fprintf (stderr, "%-5s %10ld%c %10ld%c %10ld%c\n", "Total",
1277 SCALE (G.bytes_mapped), LABEL (G.bytes_mapped),
1278 SCALE (G.allocated), LABEL(G.allocated),
1279 SCALE (total_overhead), LABEL (total_overhead));