1 /* "Bag-of-pages" garbage collector for the GNU compiler.
2 Copyright (C) 1999, 2000 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
102 /* The "" allocated string. */
105 /* A two-level tree is used to look up the page-entry for a given
106 pointer. Two chunks of the pointer's bits are extracted to index
107 the first and second levels of the tree, as follows:
111 msb +----------------+----+------+------+ lsb
117 The bottommost HOST_PAGE_SIZE_BITS are ignored, since page-entry
118 pages are aligned on system page boundaries. The next most
119 significant PAGE_L2_BITS and PAGE_L1_BITS are the second and first
120 index values in the lookup table, respectively.
122 For 32-bit architectures and the settings below, there are no
123 leftover bits. For architectures with wider pointers, the lookup
124 tree points to a list of pages, which must be scanned to find the
127 #define PAGE_L1_BITS (8)
128 #define PAGE_L2_BITS (32 - PAGE_L1_BITS - G.lg_pagesize)
129 #define PAGE_L1_SIZE ((size_t) 1 << PAGE_L1_BITS)
130 #define PAGE_L2_SIZE ((size_t) 1 << PAGE_L2_BITS)
132 #define LOOKUP_L1(p) \
133 (((size_t) (p) >> (32 - PAGE_L1_BITS)) & ((1 << PAGE_L1_BITS) - 1))
135 #define LOOKUP_L2(p) \
136 (((size_t) (p) >> G.lg_pagesize) & ((1 << PAGE_L2_BITS) - 1))
139 /* A page_entry records the status of an allocation page. This
140 structure is dynamically sized to fit the bitmap in_use_p. */
141 typedef struct page_entry
143 /* The next page-entry with objects of the same size, or NULL if
144 this is the last page-entry. */
145 struct page_entry
*next
;
147 /* The number of bytes allocated. (This will always be a multiple
148 of the host system page size.) */
151 /* The address at which the memory is allocated. */
154 /* Saved in-use bit vector for pages that aren't in the topmost
155 context during collection. */
156 unsigned long *save_in_use_p
;
158 /* Context depth of this page. */
159 unsigned short context_depth
;
161 /* The number of free objects remaining on this page. */
162 unsigned short num_free_objects
;
164 /* A likely candidate for the bit position of a free object for the
165 next allocation from this page. */
166 unsigned short next_bit_hint
;
168 /* The lg of size of objects allocated from this page. */
171 /* A bit vector indicating whether or not objects are in use. The
172 Nth bit is one if the Nth object on this page is allocated. This
173 array is dynamically sized. */
174 unsigned long in_use_p
[1];
178 #if HOST_BITS_PER_PTR <= 32
180 /* On 32-bit hosts, we use a two level page table, as pictured above. */
181 typedef page_entry
**page_table
[PAGE_L1_SIZE
];
185 /* On 64-bit hosts, we use the same two level page tables plus a linked
186 list that disambiguates the top 32-bits. There will almost always be
187 exactly one entry in the list. */
188 typedef struct page_table_chain
190 struct page_table_chain
*next
;
192 page_entry
**table
[PAGE_L1_SIZE
];
197 /* The rest of the global variables. */
198 static struct globals
200 /* The Nth element in this array is a page with objects of size 2^N.
201 If there are any pages with free objects, they will be at the
202 head of the list. NULL if there are no page-entries for this
204 page_entry
*pages
[HOST_BITS_PER_PTR
];
206 /* The Nth element in this array is the last page with objects of
207 size 2^N. NULL if there are no page-entries for this object
209 page_entry
*page_tails
[HOST_BITS_PER_PTR
];
211 /* Lookup table for associating allocation pages with object addresses. */
214 /* The system's page size. */
218 /* Bytes currently allocated. */
221 /* Bytes currently allocated at the end of the last collection. */
222 size_t allocated_last_gc
;
224 /* Total amount of memory mapped. */
227 /* The current depth in the context stack. */
228 unsigned short context_depth
;
230 /* A file descriptor open to /dev/zero for reading. */
231 #if defined (HAVE_MMAP_ANYWHERE) && !defined(MAP_ANONYMOUS)
235 /* A cache of free system pages. */
236 page_entry
*free_pages
;
238 /* The file descriptor for debugging output. */
243 /* Compute DIVIDEND / DIVISOR, rounded up. */
244 #define DIV_ROUND_UP(Dividend, Divisor) \
245 (((Dividend) + (Divisor) - 1) / (Divisor))
247 /* The number of objects per allocation page, for objects of size
249 #define OBJECTS_PER_PAGE(Order) \
250 ((Order) >= G.lg_pagesize ? 1 : G.pagesize / ((size_t)1 << (Order)))
252 /* The size in bytes required to maintain a bitmap for the objects
254 #define BITMAP_SIZE(Num_objects) \
255 (DIV_ROUND_UP ((Num_objects), HOST_BITS_PER_LONG) * sizeof(long))
257 /* Skip garbage collection if the current allocation is not at least
258 this factor times the allocation at the end of the last collection.
259 In other words, total allocation must expand by (this factor minus
260 one) before collection is performed. */
261 #define GGC_MIN_EXPAND_FOR_GC (1.3)
263 /* Bound `allocated_last_gc' to 4MB, to prevent the memory expansion
264 test from triggering too often when the heap is small. */
265 #define GGC_MIN_LAST_ALLOCATED (4 * 1024 * 1024)
268 static int ggc_allocated_p
PARAMS ((const void *));
269 static page_entry
*lookup_page_table_entry
PARAMS ((const void *));
270 static void set_page_table_entry
PARAMS ((void *, page_entry
*));
271 static char *alloc_anon
PARAMS ((char *, size_t));
272 static struct page_entry
* alloc_page
PARAMS ((unsigned));
273 static void free_page
PARAMS ((struct page_entry
*));
274 static void release_pages
PARAMS ((void));
275 static void clear_marks
PARAMS ((void));
276 static void sweep_pages
PARAMS ((void));
277 static void ggc_recalculate_in_use_p
PARAMS ((page_entry
*));
280 static void poison_pages
PARAMS ((void));
283 void debug_print_page_list
PARAMS ((int));
285 /* Returns non-zero if P was allocated in GC'able memory. */
294 #if HOST_BITS_PER_PTR <= 32
297 page_table table
= G
.lookup
;
298 size_t high_bits
= (size_t) p
& ~ (size_t) 0xffffffff;
303 if (table
->high_bits
== high_bits
)
307 base
= &table
->table
[0];
310 /* Extract the level 1 and 2 indicies. */
314 return base
[L1
] && base
[L1
][L2
];
317 /* Traverse the page table and find the entry for a page.
318 Die (probably) if the object wasn't allocated via GC. */
320 static inline page_entry
*
321 lookup_page_table_entry(p
)
327 #if HOST_BITS_PER_PTR <= 32
330 page_table table
= G
.lookup
;
331 size_t high_bits
= (size_t) p
& ~ (size_t) 0xffffffff;
332 while (table
->high_bits
!= high_bits
)
334 base
= &table
->table
[0];
337 /* Extract the level 1 and 2 indicies. */
344 /* Set the page table entry for a page. */
347 set_page_table_entry(p
, entry
)
354 #if HOST_BITS_PER_PTR <= 32
358 size_t high_bits
= (size_t) p
& ~ (size_t) 0xffffffff;
359 for (table
= G
.lookup
; table
; table
= table
->next
)
360 if (table
->high_bits
== high_bits
)
363 /* Not found -- allocate a new table. */
364 table
= (page_table
) xcalloc (1, sizeof(*table
));
365 table
->next
= G
.lookup
;
366 table
->high_bits
= high_bits
;
369 base
= &table
->table
[0];
372 /* Extract the level 1 and 2 indicies. */
376 if (base
[L1
] == NULL
)
377 base
[L1
] = (page_entry
**) xcalloc (PAGE_L2_SIZE
, sizeof (page_entry
*));
379 base
[L1
][L2
] = entry
;
382 /* Prints the page-entry for object size ORDER, for debugging. */
385 debug_print_page_list (order
)
389 printf ("Head=%p, Tail=%p:\n", G
.pages
[order
], G
.page_tails
[order
]);
393 printf ("%p(%1d|%3d) -> ", p
, p
->context_depth
, p
->num_free_objects
);
400 /* Allocate SIZE bytes of anonymous memory, preferably near PREF,
404 alloc_anon (pref
, size
)
405 char *pref ATTRIBUTE_UNUSED
;
410 #ifdef HAVE_MMAP_ANYWHERE
412 page
= (char *) mmap (pref
, size
, PROT_READ
| PROT_WRITE
,
413 MAP_PRIVATE
| MAP_ANONYMOUS
, -1, 0);
415 page
= (char *) mmap (pref
, size
, PROT_READ
| PROT_WRITE
,
416 MAP_PRIVATE
, G
.dev_zero_fd
, 0);
418 if (page
== (char *) MAP_FAILED
)
420 fputs ("Virtual memory exhausted!\n", stderr
);
425 page
= (char *) valloc (size
);
428 fputs ("Virtual memory exhausted!\n", stderr
);
431 #endif /* HAVE_VALLOC */
432 #endif /* HAVE_MMAP_ANYWHERE */
434 /* Remember that we allocated this memory. */
435 G
.bytes_mapped
+= size
;
440 /* Allocate a new page for allocating objects of size 2^ORDER,
441 and return an entry for it. The entry is not added to the
442 appropriate page_table list. */
444 static inline struct page_entry
*
448 struct page_entry
*entry
, *p
, **pp
;
452 size_t page_entry_size
;
455 num_objects
= OBJECTS_PER_PAGE (order
);
456 bitmap_size
= BITMAP_SIZE (num_objects
+ 1);
457 page_entry_size
= sizeof (page_entry
) - sizeof (long) + bitmap_size
;
458 entry_size
= num_objects
* (1 << order
);
463 /* Check the list of free pages for one we can use. */
464 for (pp
= &G
.free_pages
, p
= *pp
; p
; pp
= &p
->next
, p
= *pp
)
465 if (p
->bytes
== entry_size
)
470 /* Recycle the allocated memory from this page ... */
473 /* ... and, if possible, the page entry itself. */
474 if (p
->order
== order
)
477 memset (entry
, 0, page_entry_size
);
484 /* Actually allocate the memory. */
485 page
= alloc_anon (NULL
, entry_size
);
489 entry
= (struct page_entry
*) xcalloc (1, page_entry_size
);
491 entry
->bytes
= entry_size
;
493 entry
->context_depth
= G
.context_depth
;
494 entry
->order
= order
;
495 entry
->num_free_objects
= num_objects
;
496 entry
->next_bit_hint
= 1;
498 /* Set the one-past-the-end in-use bit. This acts as a sentry as we
499 increment the hint. */
500 entry
->in_use_p
[num_objects
/ HOST_BITS_PER_LONG
]
501 = (unsigned long) 1 << (num_objects
% HOST_BITS_PER_LONG
);
503 set_page_table_entry (page
, entry
);
505 if (GGC_DEBUG_LEVEL
>= 2)
506 fprintf (G
.debug_file
,
507 "Allocating page at %p, object size=%d, data %p-%p\n", entry
,
508 1 << order
, page
, page
+ entry_size
- 1);
513 /* For a page that is no longer needed, put it on the free page list. */
519 if (GGC_DEBUG_LEVEL
>= 2)
520 fprintf (G
.debug_file
,
521 "Deallocating page at %p, data %p-%p\n", entry
,
522 entry
->page
, entry
->page
+ entry
->bytes
- 1);
524 set_page_table_entry (entry
->page
, NULL
);
526 entry
->next
= G
.free_pages
;
527 G
.free_pages
= entry
;
530 /* Release the free page cache to the system. */
535 #ifdef HAVE_MMAP_ANYWHERE
536 page_entry
*p
, *next
;
553 /* Gather up adjacent pages so they are unmapped together. */
554 if (p
->page
== start
+ len
)
559 G
.bytes_mapped
-= len
;
568 G
.bytes_mapped
-= len
;
571 page_entry
*p
, *next
;
573 for (p
= G
.free_pages
; p
; p
= next
)
577 G
.bytes_mapped
-= p
->bytes
;
580 #endif /* HAVE_VALLOC */
581 #endif /* HAVE_MMAP_ANYWHERE */
586 /* This table provides a fast way to determine ceil(log_2(size)) for
587 allocation requests. The minimum allocation size is four bytes. */
589 static unsigned char const size_lookup
[257] =
591 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4,
592 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
593 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
594 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
595 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
596 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
597 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
598 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
599 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
600 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
601 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
602 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
603 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
604 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
605 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
606 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
610 /* Allocate a chunk of memory of SIZE bytes. If ZERO is non-zero, the
611 memory is zeroed; otherwise, its contents are undefined. */
614 ggc_alloc_obj (size
, zero
)
618 unsigned order
, word
, bit
, object_offset
;
619 struct page_entry
*entry
;
623 order
= size_lookup
[size
];
627 while (size
> ((size_t) 1 << order
))
631 /* If there are non-full pages for this size allocation, they are at
632 the head of the list. */
633 entry
= G
.pages
[order
];
635 /* If there is no page for this object size, or all pages in this
636 context are full, allocate a new page. */
637 if (entry
== NULL
|| entry
->num_free_objects
== 0)
639 struct page_entry
*new_entry
;
640 new_entry
= alloc_page (order
);
642 /* If this is the only entry, it's also the tail. */
644 G
.page_tails
[order
] = new_entry
;
646 /* Put new pages at the head of the page list. */
647 new_entry
->next
= entry
;
649 G
.pages
[order
] = new_entry
;
651 /* For a new page, we know the word and bit positions (in the
652 in_use bitmap) of the first available object -- they're zero. */
653 new_entry
->next_bit_hint
= 1;
660 /* First try to use the hint left from the previous allocation
661 to locate a clear bit in the in-use bitmap. We've made sure
662 that the one-past-the-end bit is always set, so if the hint
663 has run over, this test will fail. */
664 unsigned hint
= entry
->next_bit_hint
;
665 word
= hint
/ HOST_BITS_PER_LONG
;
666 bit
= hint
% HOST_BITS_PER_LONG
;
668 /* If the hint didn't work, scan the bitmap from the beginning. */
669 if ((entry
->in_use_p
[word
] >> bit
) & 1)
672 while (~entry
->in_use_p
[word
] == 0)
674 while ((entry
->in_use_p
[word
] >> bit
) & 1)
676 hint
= word
* HOST_BITS_PER_LONG
+ bit
;
679 /* Next time, try the next bit. */
680 entry
->next_bit_hint
= hint
+ 1;
682 object_offset
= hint
<< order
;
685 /* Set the in-use bit. */
686 entry
->in_use_p
[word
] |= ((unsigned long) 1 << bit
);
688 /* Keep a running total of the number of free objects. If this page
689 fills up, we may have to move it to the end of the list if the
690 next page isn't full. If the next page is full, all subsequent
691 pages are full, so there's no need to move it. */
692 if (--entry
->num_free_objects
== 0
693 && entry
->next
!= NULL
694 && entry
->next
->num_free_objects
> 0)
696 G
.pages
[order
] = entry
->next
;
698 G
.page_tails
[order
]->next
= entry
;
699 G
.page_tails
[order
] = entry
;
702 /* Calculate the object's address. */
703 result
= entry
->page
+ object_offset
;
706 /* `Poison' the entire allocated object before zeroing the requested area,
707 so that bytes beyond the end, if any, will not necessarily be zero. */
708 memset (result
, 0xaf, 1 << order
);
712 memset (result
, 0, size
);
714 /* Keep track of how many bytes are being allocated. This
715 information is used in deciding when to collect. */
716 G
.allocated
+= (size_t) 1 << order
;
718 if (GGC_DEBUG_LEVEL
>= 3)
719 fprintf (G
.debug_file
,
720 "Allocating object, requested size=%d, actual=%d at %p on %p\n",
721 (int) size
, 1 << order
, result
, entry
);
726 /* If P is not marked, marks it and return false. Otherwise return true.
727 P must have been allocated by the GC allocator; it mustn't point to
728 static objects, stack variables, or memory allocated with malloc. */
738 /* Look up the page on which the object is alloced. If the object
739 wasn't allocated by the collector, we'll probably die. */
740 entry
= lookup_page_table_entry (p
);
741 #ifdef ENABLE_CHECKING
746 /* Calculate the index of the object on the page; this is its bit
747 position in the in_use_p bitmap. */
748 bit
= (((const char *) p
) - entry
->page
) >> entry
->order
;
749 word
= bit
/ HOST_BITS_PER_LONG
;
750 mask
= (unsigned long) 1 << (bit
% HOST_BITS_PER_LONG
);
752 /* If the bit was previously set, skip it. */
753 if (entry
->in_use_p
[word
] & mask
)
756 /* Otherwise set it, and decrement the free object count. */
757 entry
->in_use_p
[word
] |= mask
;
758 entry
->num_free_objects
-= 1;
760 G
.allocated
+= (size_t) 1 << entry
->order
;
762 if (GGC_DEBUG_LEVEL
>= 4)
763 fprintf (G
.debug_file
, "Marking %p\n", p
);
768 /* Mark P, but check first that it was allocated by the collector. */
771 ggc_mark_if_gcable (p
)
774 if (p
&& ggc_allocated_p (p
))
778 /* Return the size of the gc-able object P. */
784 page_entry
*pe
= lookup_page_table_entry (p
);
785 return 1 << pe
->order
;
788 /* Initialize the ggc-mmap allocator. */
793 G
.pagesize
= getpagesize();
794 G
.lg_pagesize
= exact_log2 (G
.pagesize
);
796 #if defined (HAVE_MMAP_ANYWHERE) && !defined(MAP_ANONYMOUS)
797 G
.dev_zero_fd
= open ("/dev/zero", O_RDONLY
);
798 if (G
.dev_zero_fd
== -1)
803 G
.debug_file
= fopen ("ggc-mmap.debug", "w");
805 G
.debug_file
= stdout
;
808 G
.allocated_last_gc
= GGC_MIN_LAST_ALLOCATED
;
810 #ifdef HAVE_MMAP_ANYWHERE
811 /* StunOS has an amazing off-by-one error for the first mmap allocation
812 after fiddling with RLIMIT_STACK. The result, as hard as it is to
813 believe, is an unaligned page allocation, which would cause us to
814 hork badly if we tried to use it. */
816 char *p
= alloc_anon (NULL
, G
.pagesize
);
817 if ((size_t)p
& (G
.pagesize
- 1))
819 /* How losing. Discard this one and try another. If we still
820 can't get something useful, give up. */
822 p
= alloc_anon (NULL
, G
.pagesize
);
823 if ((size_t)p
& (G
.pagesize
- 1))
826 munmap (p
, G
.pagesize
);
830 empty_string
= ggc_alloc_string ("", 0);
831 ggc_add_string_root (&empty_string
, 1);
834 /* Increment the `GC context'. Objects allocated in an outer context
835 are never freed, eliminating the need to register their roots. */
843 if (G
.context_depth
== 0)
847 /* Merge the SAVE_IN_USE_P and IN_USE_P arrays in P so that IN_USE_P
848 reflects reality. Recalculate NUM_FREE_OBJECTS as well. */
851 ggc_recalculate_in_use_p (p
)
857 /* Because the past-the-end bit in in_use_p is always set, we
858 pretend there is one additional object. */
859 num_objects
= OBJECTS_PER_PAGE (p
->order
) + 1;
861 /* Reset the free object count. */
862 p
->num_free_objects
= num_objects
;
864 /* Combine the IN_USE_P and SAVE_IN_USE_P arrays. */
866 i
< DIV_ROUND_UP (BITMAP_SIZE (num_objects
),
867 sizeof (*p
->in_use_p
));
872 /* Something is in use if it is marked, or if it was in use in a
873 context further down the context stack. */
874 p
->in_use_p
[i
] |= p
->save_in_use_p
[i
];
876 /* Decrement the free object count for every object allocated. */
877 for (j
= p
->in_use_p
[i
]; j
; j
>>= 1)
878 p
->num_free_objects
-= (j
& 1);
881 if (p
->num_free_objects
>= num_objects
)
885 /* Decrement the `GC context'. All objects allocated since the
886 previous ggc_push_context are migrated to the outer context. */
891 unsigned order
, depth
;
893 depth
= --G
.context_depth
;
895 /* Any remaining pages in the popped context are lowered to the new
896 current context; i.e. objects allocated in the popped context and
897 left over are imported into the previous context. */
898 for (order
= 2; order
< HOST_BITS_PER_PTR
; order
++)
902 for (p
= G
.pages
[order
]; p
!= NULL
; p
= p
->next
)
904 if (p
->context_depth
> depth
)
905 p
->context_depth
= depth
;
907 /* If this page is now in the topmost context, and we'd
908 saved its allocation state, restore it. */
909 else if (p
->context_depth
== depth
&& p
->save_in_use_p
)
911 ggc_recalculate_in_use_p (p
);
912 free (p
->save_in_use_p
);
913 p
->save_in_use_p
= 0;
919 /* Unmark all objects. */
926 for (order
= 2; order
< HOST_BITS_PER_PTR
; order
++)
928 size_t num_objects
= OBJECTS_PER_PAGE (order
);
929 size_t bitmap_size
= BITMAP_SIZE (num_objects
+ 1);
932 for (p
= G
.pages
[order
]; p
!= NULL
; p
= p
->next
)
934 #ifdef ENABLE_CHECKING
935 /* The data should be page-aligned. */
936 if ((size_t) p
->page
& (G
.pagesize
- 1))
940 /* Pages that aren't in the topmost context are not collected;
941 nevertheless, we need their in-use bit vectors to store GC
942 marks. So, back them up first. */
943 if (p
->context_depth
< G
.context_depth
)
945 if (! p
->save_in_use_p
)
946 p
->save_in_use_p
= xmalloc (bitmap_size
);
947 memcpy (p
->save_in_use_p
, p
->in_use_p
, bitmap_size
);
950 /* Reset reset the number of free objects and clear the
951 in-use bits. These will be adjusted by mark_obj. */
952 p
->num_free_objects
= num_objects
;
953 memset (p
->in_use_p
, 0, bitmap_size
);
955 /* Make sure the one-past-the-end bit is always set. */
956 p
->in_use_p
[num_objects
/ HOST_BITS_PER_LONG
]
957 = ((unsigned long) 1 << (num_objects
% HOST_BITS_PER_LONG
));
962 /* Free all empty pages. Partially empty pages need no attention
963 because the `mark' bit doubles as an `unused' bit. */
970 for (order
= 2; order
< HOST_BITS_PER_PTR
; order
++)
972 /* The last page-entry to consider, regardless of entries
973 placed at the end of the list. */
974 page_entry
* const last
= G
.page_tails
[order
];
976 size_t num_objects
= OBJECTS_PER_PAGE (order
);
977 page_entry
*p
, *previous
;
987 page_entry
*next
= p
->next
;
989 /* Loop until all entries have been examined. */
992 /* Only objects on pages in the topmost context should get
994 if (p
->context_depth
< G
.context_depth
)
997 /* Remove the page if it's empty. */
998 else if (p
->num_free_objects
== num_objects
)
1001 G
.pages
[order
] = next
;
1003 previous
->next
= next
;
1005 /* Are we removing the last element? */
1006 if (p
== G
.page_tails
[order
])
1007 G
.page_tails
[order
] = previous
;
1012 /* If the page is full, move it to the end. */
1013 else if (p
->num_free_objects
== 0)
1015 /* Don't move it if it's already at the end. */
1016 if (p
!= G
.page_tails
[order
])
1018 /* Move p to the end of the list. */
1020 G
.page_tails
[order
]->next
= p
;
1022 /* Update the tail pointer... */
1023 G
.page_tails
[order
] = p
;
1025 /* ... and the head pointer, if necessary. */
1027 G
.pages
[order
] = next
;
1029 previous
->next
= next
;
1034 /* If we've fallen through to here, it's a page in the
1035 topmost context that is neither full nor empty. Such a
1036 page must precede pages at lesser context depth in the
1037 list, so move it to the head. */
1038 else if (p
!= G
.pages
[order
])
1040 previous
->next
= p
->next
;
1041 p
->next
= G
.pages
[order
];
1043 /* Are we moving the last element? */
1044 if (G
.page_tails
[order
] == p
)
1045 G
.page_tails
[order
] = previous
;
1054 /* Now, restore the in_use_p vectors for any pages from contexts
1055 other than the current one. */
1056 for (p
= G
.pages
[order
]; p
; p
= p
->next
)
1057 if (p
->context_depth
!= G
.context_depth
)
1058 ggc_recalculate_in_use_p (p
);
1063 /* Clobber all free objects. */
1070 for (order
= 2; order
< HOST_BITS_PER_PTR
; order
++)
1072 size_t num_objects
= OBJECTS_PER_PAGE (order
);
1073 size_t size
= (size_t) 1 << order
;
1076 for (p
= G
.pages
[order
]; p
!= NULL
; p
= p
->next
)
1080 if (p
->context_depth
!= G
.context_depth
)
1081 /* Since we don't do any collection for pages in pushed
1082 contexts, there's no need to do any poisoning. And
1083 besides, the IN_USE_P array isn't valid until we pop
1087 for (i
= 0; i
< num_objects
; i
++)
1090 word
= i
/ HOST_BITS_PER_LONG
;
1091 bit
= i
% HOST_BITS_PER_LONG
;
1092 if (((p
->in_use_p
[word
] >> bit
) & 1) == 0)
1093 memset (p
->page
+ i
* size
, 0xa5, size
);
1100 /* Top level mark-and-sweep routine. */
1105 /* Avoid frequent unnecessary work by skipping collection if the
1106 total allocations haven't expanded much since the last
1108 #ifndef GGC_ALWAYS_COLLECT
1109 if (G
.allocated
< GGC_MIN_EXPAND_FOR_GC
* G
.allocated_last_gc
)
1113 timevar_push (TV_GC
);
1115 fprintf (stderr
, " {GC %luk -> ", (unsigned long) G
.allocated
/ 1024);
1117 /* Zero the total allocated bytes. We'll reaccumulate this while
1121 /* Release the pages we freed the last time we collected, but didn't
1122 reuse in the interim. */
1134 G
.allocated_last_gc
= G
.allocated
;
1135 if (G
.allocated_last_gc
< GGC_MIN_LAST_ALLOCATED
)
1136 G
.allocated_last_gc
= GGC_MIN_LAST_ALLOCATED
;
1138 timevar_pop (TV_GC
);
1141 fprintf (stderr
, "%luk}", (unsigned long) G
.allocated
/ 1024);
1144 /* Print allocation statistics. */
1147 ggc_page_print_statistics ()
1149 struct ggc_statistics stats
;
1152 /* Clear the statistics. */
1153 memset (&stats
, 0, sizeof (stats
));
1155 /* Make sure collection will really occur. */
1156 G
.allocated_last_gc
= 0;
1158 /* Collect and print the statistics common across collectors. */
1159 ggc_print_statistics (stderr
, &stats
);
1161 /* Release free pages so that we will not count the bytes allocated
1162 there as part of the total allocated memory. */
1165 /* Collect some information about the various sizes of
1167 fprintf (stderr
, "\n%-4s%-16s%-16s\n", "Log", "Allocated", "Used");
1168 for (i
= 0; i
< HOST_BITS_PER_PTR
; ++i
)
1174 /* Skip empty entries. */
1178 allocated
= in_use
= 0;
1180 /* Figure out the total number of bytes allocated for objects of
1181 this size, and how many of them are actually in use. */
1182 for (p
= G
.pages
[i
]; p
; p
= p
->next
)
1184 allocated
+= p
->bytes
;
1186 (OBJECTS_PER_PAGE (i
) - p
->num_free_objects
) * (1 << i
);
1188 fprintf (stderr
, "%-3d %-15lu %-15lu\n", i
,
1189 (unsigned long) allocated
, (unsigned long) in_use
);
1192 /* Print out some global information. */
1193 fprintf (stderr
, "\nTotal bytes marked: %lu\n",
1194 (unsigned long) G
.allocated
);
1195 fprintf (stderr
, "Total bytes mapped: %lu\n",
1196 (unsigned long) G
.bytes_mapped
);