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 GCC.
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 2, or (at your option) any later
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to the Free
18 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
32 /* Prefer MAP_ANON(YMOUS) to /dev/zero, since we don't need to keep a
33 file open. Prefer either to valloc. */
35 # undef HAVE_MMAP_DEV_ZERO
37 # include <sys/mman.h>
39 # define MAP_FAILED -1
41 # if !defined (MAP_ANONYMOUS) && defined (MAP_ANON)
42 # define MAP_ANONYMOUS MAP_ANON
48 #ifdef HAVE_MMAP_DEV_ZERO
50 # include <sys/mman.h>
52 # define MAP_FAILED -1
59 #define USING_MALLOC_PAGE_GROUPS
64 This garbage-collecting allocator allocates objects on one of a set
65 of pages. Each page can allocate objects of a single size only;
66 available sizes are powers of two starting at four bytes. The size
67 of an allocation request is rounded up to the next power of two
68 (`order'), and satisfied from the appropriate page.
70 Each page is recorded in a page-entry, which also maintains an
71 in-use bitmap of object positions on the page. This allows the
72 allocation state of a particular object to be flipped without
73 touching the page itself.
75 Each page-entry also has a context depth, which is used to track
76 pushing and popping of allocation contexts. Only objects allocated
77 in the current (highest-numbered) context may be collected.
79 Page entries are arranged in an array of singly-linked lists. The
80 array is indexed by the allocation size, in bits, of the pages on
81 it; i.e. all pages on a list allocate objects of the same size.
82 Pages are ordered on the list such that all non-full pages precede
83 all full pages, with non-full pages arranged in order of decreasing
86 Empty pages (of all orders) are kept on a single page cache list,
87 and are considered first when new pages are required; they are
88 deallocated at the start of the next collection if they haven't
89 been recycled by then. */
92 /* Define GGC_POISON to poison memory marked unused by the collector. */
95 /* Define GGC_ALWAYS_COLLECT to perform collection every time
96 ggc_collect is invoked. Otherwise, collection is performed only
97 when a significant amount of memory has been allocated since the
99 #undef GGC_ALWAYS_COLLECT
101 #ifdef ENABLE_GC_CHECKING
104 #ifdef ENABLE_GC_ALWAYS_COLLECT
105 #define GGC_ALWAYS_COLLECT
108 /* Define GGC_DEBUG_LEVEL to print debugging information.
109 0: No debugging output.
110 1: GC statistics only.
111 2: Page-entry allocations/deallocations as well.
112 3: Object allocations as well.
113 4: Object marks as well. */
114 #define GGC_DEBUG_LEVEL (0)
116 #ifndef HOST_BITS_PER_PTR
117 #define HOST_BITS_PER_PTR HOST_BITS_PER_LONG
121 /* A two-level tree is used to look up the page-entry for a given
122 pointer. Two chunks of the pointer's bits are extracted to index
123 the first and second levels of the tree, as follows:
127 msb +----------------+----+------+------+ lsb
133 The bottommost HOST_PAGE_SIZE_BITS are ignored, since page-entry
134 pages are aligned on system page boundaries. The next most
135 significant PAGE_L2_BITS and PAGE_L1_BITS are the second and first
136 index values in the lookup table, respectively.
138 For 32-bit architectures and the settings below, there are no
139 leftover bits. For architectures with wider pointers, the lookup
140 tree points to a list of pages, which must be scanned to find the
143 #define PAGE_L1_BITS (8)
144 #define PAGE_L2_BITS (32 - PAGE_L1_BITS - G.lg_pagesize)
145 #define PAGE_L1_SIZE ((size_t) 1 << PAGE_L1_BITS)
146 #define PAGE_L2_SIZE ((size_t) 1 << PAGE_L2_BITS)
148 #define LOOKUP_L1(p) \
149 (((size_t) (p) >> (32 - PAGE_L1_BITS)) & ((1 << PAGE_L1_BITS) - 1))
151 #define LOOKUP_L2(p) \
152 (((size_t) (p) >> G.lg_pagesize) & ((1 << PAGE_L2_BITS) - 1))
154 /* The number of objects per allocation page, for objects on a page of
155 the indicated ORDER. */
156 #define OBJECTS_PER_PAGE(ORDER) objects_per_page_table[ORDER]
158 /* The size of an object on a page of the indicated ORDER. */
159 #define OBJECT_SIZE(ORDER) object_size_table[ORDER]
161 /* The number of extra orders, not corresponding to power-of-two sized
164 #define NUM_EXTRA_ORDERS \
165 (sizeof (extra_order_size_table) / sizeof (extra_order_size_table[0]))
167 /* The Ith entry is the maximum size of an object to be stored in the
168 Ith extra order. Adding a new entry to this array is the *only*
169 thing you need to do to add a new special allocation size. */
171 static const size_t extra_order_size_table
[] = {
172 sizeof (struct tree_decl
),
173 sizeof (struct tree_list
)
176 /* The total number of orders. */
178 #define NUM_ORDERS (HOST_BITS_PER_PTR + NUM_EXTRA_ORDERS)
180 /* We use this structure to determine the alignment required for
181 allocations. For power-of-two sized allocations, that's not a
182 problem, but it does matter for odd-sized allocations. */
184 struct max_alignment
{
188 #ifdef HAVE_LONG_DOUBLE
196 /* The biggest alignment required. */
198 #define MAX_ALIGNMENT (offsetof (struct max_alignment, u))
200 /* The Ith entry is the number of objects on a page or order I. */
202 static unsigned objects_per_page_table
[NUM_ORDERS
];
204 /* The Ith entry is the size of an object on a page of order I. */
206 static size_t object_size_table
[NUM_ORDERS
];
208 /* A page_entry records the status of an allocation page. This
209 structure is dynamically sized to fit the bitmap in_use_p. */
210 typedef struct page_entry
212 /* The next page-entry with objects of the same size, or NULL if
213 this is the last page-entry. */
214 struct page_entry
*next
;
216 /* The number of bytes allocated. (This will always be a multiple
217 of the host system page size.) */
220 /* The address at which the memory is allocated. */
223 #ifdef USING_MALLOC_PAGE_GROUPS
224 /* Back pointer to the page group this page came from. */
225 struct page_group
*group
;
228 /* Saved in-use bit vector for pages that aren't in the topmost
229 context during collection. */
230 unsigned long *save_in_use_p
;
232 /* Context depth of this page. */
233 unsigned short context_depth
;
235 /* The number of free objects remaining on this page. */
236 unsigned short num_free_objects
;
238 /* A likely candidate for the bit position of a free object for the
239 next allocation from this page. */
240 unsigned short next_bit_hint
;
242 /* The lg of size of objects allocated from this page. */
245 /* A bit vector indicating whether or not objects are in use. The
246 Nth bit is one if the Nth object on this page is allocated. This
247 array is dynamically sized. */
248 unsigned long in_use_p
[1];
251 #ifdef USING_MALLOC_PAGE_GROUPS
252 /* A page_group describes a large allocation from malloc, from which
253 we parcel out aligned pages. */
254 typedef struct page_group
256 /* A linked list of all extant page groups. */
257 struct page_group
*next
;
259 /* The address we received from malloc. */
262 /* The size of the block. */
265 /* A bitmask of pages in use. */
270 #if HOST_BITS_PER_PTR <= 32
272 /* On 32-bit hosts, we use a two level page table, as pictured above. */
273 typedef page_entry
**page_table
[PAGE_L1_SIZE
];
277 /* On 64-bit hosts, we use the same two level page tables plus a linked
278 list that disambiguates the top 32-bits. There will almost always be
279 exactly one entry in the list. */
280 typedef struct page_table_chain
282 struct page_table_chain
*next
;
284 page_entry
**table
[PAGE_L1_SIZE
];
289 /* The rest of the global variables. */
290 static struct globals
292 /* The Nth element in this array is a page with objects of size 2^N.
293 If there are any pages with free objects, they will be at the
294 head of the list. NULL if there are no page-entries for this
296 page_entry
*pages
[NUM_ORDERS
];
298 /* The Nth element in this array is the last page with objects of
299 size 2^N. NULL if there are no page-entries for this object
301 page_entry
*page_tails
[NUM_ORDERS
];
303 /* Lookup table for associating allocation pages with object addresses. */
306 /* The system's page size. */
310 /* Bytes currently allocated. */
313 /* Bytes currently allocated at the end of the last collection. */
314 size_t allocated_last_gc
;
316 /* Total amount of memory mapped. */
319 /* The current depth in the context stack. */
320 unsigned short context_depth
;
322 /* A file descriptor open to /dev/zero for reading. */
323 #if defined (HAVE_MMAP_DEV_ZERO)
327 /* A cache of free system pages. */
328 page_entry
*free_pages
;
330 #ifdef USING_MALLOC_PAGE_GROUPS
331 page_group
*page_groups
;
334 /* The file descriptor for debugging output. */
338 /* The size in bytes required to maintain a bitmap for the objects
340 #define BITMAP_SIZE(Num_objects) \
341 (CEIL ((Num_objects), HOST_BITS_PER_LONG) * sizeof(long))
343 /* Skip garbage collection if the current allocation is not at least
344 this factor times the allocation at the end of the last collection.
345 In other words, total allocation must expand by (this factor minus
346 one) before collection is performed. */
347 #define GGC_MIN_EXPAND_FOR_GC (1.3)
349 /* Bound `allocated_last_gc' to 4MB, to prevent the memory expansion
350 test from triggering too often when the heap is small. */
351 #define GGC_MIN_LAST_ALLOCATED (4 * 1024 * 1024)
353 /* Allocate pages in chunks of this size, to throttle calls to memory
354 allocation routines. The first page is used, the rest go onto the
355 free list. This cannot be larger than HOST_BITS_PER_INT for the
356 in_use bitmask for page_group. */
357 #define GGC_QUIRE_SIZE 16
359 static int ggc_allocated_p
PARAMS ((const void *));
360 static page_entry
*lookup_page_table_entry
PARAMS ((const void *));
361 static void set_page_table_entry
PARAMS ((void *, page_entry
*));
363 static char *alloc_anon
PARAMS ((char *, size_t));
365 #ifdef USING_MALLOC_PAGE_GROUPS
366 static size_t page_group_index
PARAMS ((char *, char *));
367 static void set_page_group_in_use
PARAMS ((page_group
*, char *));
368 static void clear_page_group_in_use
PARAMS ((page_group
*, char *));
370 static struct page_entry
* alloc_page
PARAMS ((unsigned));
371 static void free_page
PARAMS ((struct page_entry
*));
372 static void release_pages
PARAMS ((void));
373 static void clear_marks
PARAMS ((void));
374 static void sweep_pages
PARAMS ((void));
375 static void ggc_recalculate_in_use_p
PARAMS ((page_entry
*));
378 static void poison_pages
PARAMS ((void));
381 void debug_print_page_list
PARAMS ((int));
383 /* Returns non-zero if P was allocated in GC'able memory. */
392 #if HOST_BITS_PER_PTR <= 32
395 page_table table
= G
.lookup
;
396 size_t high_bits
= (size_t) p
& ~ (size_t) 0xffffffff;
401 if (table
->high_bits
== high_bits
)
405 base
= &table
->table
[0];
408 /* Extract the level 1 and 2 indices. */
412 return base
[L1
] && base
[L1
][L2
];
415 /* Traverse the page table and find the entry for a page.
416 Die (probably) if the object wasn't allocated via GC. */
418 static inline page_entry
*
419 lookup_page_table_entry(p
)
425 #if HOST_BITS_PER_PTR <= 32
428 page_table table
= G
.lookup
;
429 size_t high_bits
= (size_t) p
& ~ (size_t) 0xffffffff;
430 while (table
->high_bits
!= high_bits
)
432 base
= &table
->table
[0];
435 /* Extract the level 1 and 2 indices. */
442 /* Set the page table entry for a page. */
445 set_page_table_entry(p
, entry
)
452 #if HOST_BITS_PER_PTR <= 32
456 size_t high_bits
= (size_t) p
& ~ (size_t) 0xffffffff;
457 for (table
= G
.lookup
; table
; table
= table
->next
)
458 if (table
->high_bits
== high_bits
)
461 /* Not found -- allocate a new table. */
462 table
= (page_table
) xcalloc (1, sizeof(*table
));
463 table
->next
= G
.lookup
;
464 table
->high_bits
= high_bits
;
467 base
= &table
->table
[0];
470 /* Extract the level 1 and 2 indices. */
474 if (base
[L1
] == NULL
)
475 base
[L1
] = (page_entry
**) xcalloc (PAGE_L2_SIZE
, sizeof (page_entry
*));
477 base
[L1
][L2
] = entry
;
480 /* Prints the page-entry for object size ORDER, for debugging. */
483 debug_print_page_list (order
)
487 printf ("Head=%p, Tail=%p:\n", (PTR
) G
.pages
[order
],
488 (PTR
) G
.page_tails
[order
]);
492 printf ("%p(%1d|%3d) -> ", (PTR
) p
, p
->context_depth
,
493 p
->num_free_objects
);
501 /* Allocate SIZE bytes of anonymous memory, preferably near PREF,
502 (if non-null). The ifdef structure here is intended to cause a
503 compile error unless exactly one of the HAVE_* is defined. */
506 alloc_anon (pref
, size
)
507 char *pref ATTRIBUTE_UNUSED
;
510 #ifdef HAVE_MMAP_ANON
511 char *page
= (char *) mmap (pref
, size
, PROT_READ
| PROT_WRITE
,
512 MAP_PRIVATE
| MAP_ANONYMOUS
, -1, 0);
514 #ifdef HAVE_MMAP_DEV_ZERO
515 char *page
= (char *) mmap (pref
, size
, PROT_READ
| PROT_WRITE
,
516 MAP_PRIVATE
, G
.dev_zero_fd
, 0);
519 if (page
== (char *) MAP_FAILED
)
521 perror ("Virtual memory exhausted");
522 exit (FATAL_EXIT_CODE
);
525 /* Remember that we allocated this memory. */
526 G
.bytes_mapped
+= size
;
531 #ifdef USING_MALLOC_PAGE_GROUPS
532 /* Compute the index for this page into the page group. */
535 page_group_index (allocation
, page
)
536 char *allocation
, *page
;
538 return (size_t)(page
- allocation
) >> G
.lg_pagesize
;
541 /* Set and clear the in_use bit for this page in the page group. */
544 set_page_group_in_use (group
, page
)
548 group
->in_use
|= 1 << page_group_index (group
->allocation
, page
);
552 clear_page_group_in_use (group
, page
)
556 group
->in_use
&= ~(1 << page_group_index (group
->allocation
, page
));
560 /* Allocate a new page for allocating objects of size 2^ORDER,
561 and return an entry for it. The entry is not added to the
562 appropriate page_table list. */
564 static inline struct page_entry
*
568 struct page_entry
*entry
, *p
, **pp
;
572 size_t page_entry_size
;
574 #ifdef USING_MALLOC_PAGE_GROUPS
578 num_objects
= OBJECTS_PER_PAGE (order
);
579 bitmap_size
= BITMAP_SIZE (num_objects
+ 1);
580 page_entry_size
= sizeof (page_entry
) - sizeof (long) + bitmap_size
;
581 entry_size
= num_objects
* OBJECT_SIZE (order
);
582 if (entry_size
< G
.pagesize
)
583 entry_size
= G
.pagesize
;
588 /* Check the list of free pages for one we can use. */
589 for (pp
= &G
.free_pages
, p
= *pp
; p
; pp
= &p
->next
, p
= *pp
)
590 if (p
->bytes
== entry_size
)
595 /* Recycle the allocated memory from this page ... */
599 #ifdef USING_MALLOC_PAGE_GROUPS
603 /* ... and, if possible, the page entry itself. */
604 if (p
->order
== order
)
607 memset (entry
, 0, page_entry_size
);
613 else if (entry_size
== G
.pagesize
)
615 /* We want just one page. Allocate a bunch of them and put the
616 extras on the freelist. (Can only do this optimization with
617 mmap for backing store.) */
618 struct page_entry
*e
, *f
= G
.free_pages
;
621 page
= alloc_anon (NULL
, G
.pagesize
* GGC_QUIRE_SIZE
);
623 /* This loop counts down so that the chain will be in ascending
625 for (i
= GGC_QUIRE_SIZE
- 1; i
>= 1; i
--)
627 e
= (struct page_entry
*) xcalloc (1, page_entry_size
);
629 e
->bytes
= G
.pagesize
;
630 e
->page
= page
+ (i
<< G
.lg_pagesize
);
638 page
= alloc_anon (NULL
, entry_size
);
640 #ifdef USING_MALLOC_PAGE_GROUPS
643 /* Allocate a large block of memory and serve out the aligned
644 pages therein. This results in much less memory wastage
645 than the traditional implementation of valloc. */
647 char *allocation
, *a
, *enda
;
648 size_t alloc_size
, head_slop
, tail_slop
;
649 int multiple_pages
= (entry_size
== G
.pagesize
);
652 alloc_size
= GGC_QUIRE_SIZE
* G
.pagesize
;
654 alloc_size
= entry_size
+ G
.pagesize
- 1;
655 allocation
= xmalloc (alloc_size
);
657 page
= (char *)(((size_t) allocation
+ G
.pagesize
- 1) & -G
.pagesize
);
658 head_slop
= page
- allocation
;
660 tail_slop
= ((size_t) allocation
+ alloc_size
) & (G
.pagesize
- 1);
662 tail_slop
= alloc_size
- entry_size
- head_slop
;
663 enda
= allocation
+ alloc_size
- tail_slop
;
665 /* We allocated N pages, which are likely not aligned, leaving
666 us with N-1 usable pages. We plan to place the page_group
667 structure somewhere in the slop. */
668 if (head_slop
>= sizeof (page_group
))
669 group
= (page_group
*)page
- 1;
672 /* We magically got an aligned allocation. Too bad, we have
673 to waste a page anyway. */
677 tail_slop
+= G
.pagesize
;
679 if (tail_slop
< sizeof (page_group
))
681 group
= (page_group
*)enda
;
682 tail_slop
-= sizeof (page_group
);
685 /* Remember that we allocated this memory. */
686 group
->next
= G
.page_groups
;
687 group
->allocation
= allocation
;
688 group
->alloc_size
= alloc_size
;
690 G
.page_groups
= group
;
691 G
.bytes_mapped
+= alloc_size
;
693 /* If we allocated multiple pages, put the rest on the free list. */
696 struct page_entry
*e
, *f
= G
.free_pages
;
697 for (a
= enda
- G
.pagesize
; a
!= page
; a
-= G
.pagesize
)
699 e
= (struct page_entry
*) xcalloc (1, page_entry_size
);
701 e
->bytes
= G
.pagesize
;
713 entry
= (struct page_entry
*) xcalloc (1, page_entry_size
);
715 entry
->bytes
= entry_size
;
717 entry
->context_depth
= G
.context_depth
;
718 entry
->order
= order
;
719 entry
->num_free_objects
= num_objects
;
720 entry
->next_bit_hint
= 1;
722 #ifdef USING_MALLOC_PAGE_GROUPS
723 entry
->group
= group
;
724 set_page_group_in_use (group
, page
);
727 /* Set the one-past-the-end in-use bit. This acts as a sentry as we
728 increment the hint. */
729 entry
->in_use_p
[num_objects
/ HOST_BITS_PER_LONG
]
730 = (unsigned long) 1 << (num_objects
% HOST_BITS_PER_LONG
);
732 set_page_table_entry (page
, entry
);
734 if (GGC_DEBUG_LEVEL
>= 2)
735 fprintf (G
.debug_file
,
736 "Allocating page at %p, object size=%ld, data %p-%p\n",
737 (PTR
) entry
, (long) OBJECT_SIZE (order
), page
,
738 page
+ entry_size
- 1);
743 /* For a page that is no longer needed, put it on the free page list. */
749 if (GGC_DEBUG_LEVEL
>= 2)
750 fprintf (G
.debug_file
,
751 "Deallocating page at %p, data %p-%p\n", (PTR
) entry
,
752 entry
->page
, entry
->page
+ entry
->bytes
- 1);
754 set_page_table_entry (entry
->page
, NULL
);
756 #ifdef USING_MALLOC_PAGE_GROUPS
757 clear_page_group_in_use (entry
->group
, entry
->page
);
760 entry
->next
= G
.free_pages
;
761 G
.free_pages
= entry
;
764 /* Release the free page cache to the system. */
770 page_entry
*p
, *next
;
774 /* Gather up adjacent pages so they are unmapped together. */
785 while (p
&& p
->page
== start
+ len
)
794 G
.bytes_mapped
-= len
;
799 #ifdef USING_MALLOC_PAGE_GROUPS
803 /* Remove all pages from free page groups from the list. */
805 while ((p
= *pp
) != NULL
)
806 if (p
->group
->in_use
== 0)
814 /* Remove all free page groups, and release the storage. */
816 while ((g
= *gp
) != NULL
)
820 G
.bytes_mapped
-= g
->alloc_size
;
821 free (g
->allocation
);
828 /* This table provides a fast way to determine ceil(log_2(size)) for
829 allocation requests. The minimum allocation size is eight bytes. */
831 static unsigned char size_lookup
[257] =
833 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4,
834 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
835 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
836 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
837 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
838 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
839 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
840 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
841 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
842 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
843 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
844 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
845 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
846 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
847 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
848 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
852 /* Allocate a chunk of memory of SIZE bytes. If ZERO is non-zero, the
853 memory is zeroed; otherwise, its contents are undefined. */
859 unsigned order
, word
, bit
, object_offset
;
860 struct page_entry
*entry
;
864 order
= size_lookup
[size
];
868 while (size
> OBJECT_SIZE (order
))
872 /* If there are non-full pages for this size allocation, they are at
873 the head of the list. */
874 entry
= G
.pages
[order
];
876 /* If there is no page for this object size, or all pages in this
877 context are full, allocate a new page. */
878 if (entry
== NULL
|| entry
->num_free_objects
== 0)
880 struct page_entry
*new_entry
;
881 new_entry
= alloc_page (order
);
883 /* If this is the only entry, it's also the tail. */
885 G
.page_tails
[order
] = new_entry
;
887 /* Put new pages at the head of the page list. */
888 new_entry
->next
= entry
;
890 G
.pages
[order
] = new_entry
;
892 /* For a new page, we know the word and bit positions (in the
893 in_use bitmap) of the first available object -- they're zero. */
894 new_entry
->next_bit_hint
= 1;
901 /* First try to use the hint left from the previous allocation
902 to locate a clear bit in the in-use bitmap. We've made sure
903 that the one-past-the-end bit is always set, so if the hint
904 has run over, this test will fail. */
905 unsigned hint
= entry
->next_bit_hint
;
906 word
= hint
/ HOST_BITS_PER_LONG
;
907 bit
= hint
% HOST_BITS_PER_LONG
;
909 /* If the hint didn't work, scan the bitmap from the beginning. */
910 if ((entry
->in_use_p
[word
] >> bit
) & 1)
913 while (~entry
->in_use_p
[word
] == 0)
915 while ((entry
->in_use_p
[word
] >> bit
) & 1)
917 hint
= word
* HOST_BITS_PER_LONG
+ bit
;
920 /* Next time, try the next bit. */
921 entry
->next_bit_hint
= hint
+ 1;
923 object_offset
= hint
* OBJECT_SIZE (order
);
926 /* Set the in-use bit. */
927 entry
->in_use_p
[word
] |= ((unsigned long) 1 << bit
);
929 /* Keep a running total of the number of free objects. If this page
930 fills up, we may have to move it to the end of the list if the
931 next page isn't full. If the next page is full, all subsequent
932 pages are full, so there's no need to move it. */
933 if (--entry
->num_free_objects
== 0
934 && entry
->next
!= NULL
935 && entry
->next
->num_free_objects
> 0)
937 G
.pages
[order
] = entry
->next
;
939 G
.page_tails
[order
]->next
= entry
;
940 G
.page_tails
[order
] = entry
;
943 /* Calculate the object's address. */
944 result
= entry
->page
+ object_offset
;
947 /* `Poison' the entire allocated object, including any padding at
949 memset (result
, 0xaf, OBJECT_SIZE (order
));
952 /* Keep track of how many bytes are being allocated. This
953 information is used in deciding when to collect. */
954 G
.allocated
+= OBJECT_SIZE (order
);
956 if (GGC_DEBUG_LEVEL
>= 3)
957 fprintf (G
.debug_file
,
958 "Allocating object, requested size=%ld, actual=%ld at %p on %p\n",
959 (long) size
, (long) OBJECT_SIZE (order
), result
, (PTR
) entry
);
964 /* If P is not marked, marks it and return false. Otherwise return true.
965 P must have been allocated by the GC allocator; it mustn't point to
966 static objects, stack variables, or memory allocated with malloc. */
976 /* Look up the page on which the object is alloced. If the object
977 wasn't allocated by the collector, we'll probably die. */
978 entry
= lookup_page_table_entry (p
);
979 #ifdef ENABLE_CHECKING
984 /* Calculate the index of the object on the page; this is its bit
985 position in the in_use_p bitmap. */
986 bit
= (((const char *) p
) - entry
->page
) / OBJECT_SIZE (entry
->order
);
987 word
= bit
/ HOST_BITS_PER_LONG
;
988 mask
= (unsigned long) 1 << (bit
% HOST_BITS_PER_LONG
);
990 /* If the bit was previously set, skip it. */
991 if (entry
->in_use_p
[word
] & mask
)
994 /* Otherwise set it, and decrement the free object count. */
995 entry
->in_use_p
[word
] |= mask
;
996 entry
->num_free_objects
-= 1;
998 if (GGC_DEBUG_LEVEL
>= 4)
999 fprintf (G
.debug_file
, "Marking %p\n", p
);
1004 /* Return 1 if P has been marked, zero otherwise.
1005 P must have been allocated by the GC allocator; it mustn't point to
1006 static objects, stack variables, or memory allocated with malloc. */
1016 /* Look up the page on which the object is alloced. If the object
1017 wasn't allocated by the collector, we'll probably die. */
1018 entry
= lookup_page_table_entry (p
);
1019 #ifdef ENABLE_CHECKING
1024 /* Calculate the index of the object on the page; this is its bit
1025 position in the in_use_p bitmap. */
1026 bit
= (((const char *) p
) - entry
->page
) / OBJECT_SIZE (entry
->order
);
1027 word
= bit
/ HOST_BITS_PER_LONG
;
1028 mask
= (unsigned long) 1 << (bit
% HOST_BITS_PER_LONG
);
1030 return (entry
->in_use_p
[word
] & mask
) != 0;
1033 /* Return the size of the gc-able object P. */
1039 page_entry
*pe
= lookup_page_table_entry (p
);
1040 return OBJECT_SIZE (pe
->order
);
1043 /* Initialize the ggc-mmap allocator. */
1050 G
.pagesize
= getpagesize();
1051 G
.lg_pagesize
= exact_log2 (G
.pagesize
);
1053 #ifdef HAVE_MMAP_DEV_ZERO
1054 G
.dev_zero_fd
= open ("/dev/zero", O_RDONLY
);
1055 if (G
.dev_zero_fd
== -1)
1060 G
.debug_file
= fopen ("ggc-mmap.debug", "w");
1062 G
.debug_file
= stdout
;
1065 G
.allocated_last_gc
= GGC_MIN_LAST_ALLOCATED
;
1068 /* StunOS has an amazing off-by-one error for the first mmap allocation
1069 after fiddling with RLIMIT_STACK. The result, as hard as it is to
1070 believe, is an unaligned page allocation, which would cause us to
1071 hork badly if we tried to use it. */
1073 char *p
= alloc_anon (NULL
, G
.pagesize
);
1074 struct page_entry
*e
;
1075 if ((size_t)p
& (G
.pagesize
- 1))
1077 /* How losing. Discard this one and try another. If we still
1078 can't get something useful, give up. */
1080 p
= alloc_anon (NULL
, G
.pagesize
);
1081 if ((size_t)p
& (G
.pagesize
- 1))
1085 /* We have a good page, might as well hold onto it... */
1086 e
= (struct page_entry
*) xcalloc (1, sizeof (struct page_entry
));
1087 e
->bytes
= G
.pagesize
;
1089 e
->next
= G
.free_pages
;
1094 /* Initialize the object size table. */
1095 for (order
= 0; order
< HOST_BITS_PER_PTR
; ++order
)
1096 object_size_table
[order
] = (size_t) 1 << order
;
1097 for (order
= HOST_BITS_PER_PTR
; order
< NUM_ORDERS
; ++order
)
1099 size_t s
= extra_order_size_table
[order
- HOST_BITS_PER_PTR
];
1101 /* If S is not a multiple of the MAX_ALIGNMENT, then round it up
1102 so that we're sure of getting aligned memory. */
1103 s
= CEIL (s
, MAX_ALIGNMENT
) * MAX_ALIGNMENT
;
1104 object_size_table
[order
] = s
;
1107 /* Initialize the objects-per-page table. */
1108 for (order
= 0; order
< NUM_ORDERS
; ++order
)
1110 objects_per_page_table
[order
] = G
.pagesize
/ OBJECT_SIZE (order
);
1111 if (objects_per_page_table
[order
] == 0)
1112 objects_per_page_table
[order
] = 1;
1115 /* Reset the size_lookup array to put appropriately sized objects in
1116 the special orders. All objects bigger than the previous power
1117 of two, but no greater than the special size, should go in the
1119 for (order
= HOST_BITS_PER_PTR
; order
< NUM_ORDERS
; ++order
)
1124 o
= size_lookup
[OBJECT_SIZE (order
)];
1125 for (i
= OBJECT_SIZE (order
); size_lookup
[i
] == o
; --i
)
1126 size_lookup
[i
] = order
;
1130 /* Increment the `GC context'. Objects allocated in an outer context
1131 are never freed, eliminating the need to register their roots. */
1139 if (G
.context_depth
== 0)
1143 /* Merge the SAVE_IN_USE_P and IN_USE_P arrays in P so that IN_USE_P
1144 reflects reality. Recalculate NUM_FREE_OBJECTS as well. */
1147 ggc_recalculate_in_use_p (p
)
1153 /* Because the past-the-end bit in in_use_p is always set, we
1154 pretend there is one additional object. */
1155 num_objects
= OBJECTS_PER_PAGE (p
->order
) + 1;
1157 /* Reset the free object count. */
1158 p
->num_free_objects
= num_objects
;
1160 /* Combine the IN_USE_P and SAVE_IN_USE_P arrays. */
1162 i
< CEIL (BITMAP_SIZE (num_objects
),
1163 sizeof (*p
->in_use_p
));
1168 /* Something is in use if it is marked, or if it was in use in a
1169 context further down the context stack. */
1170 p
->in_use_p
[i
] |= p
->save_in_use_p
[i
];
1172 /* Decrement the free object count for every object allocated. */
1173 for (j
= p
->in_use_p
[i
]; j
; j
>>= 1)
1174 p
->num_free_objects
-= (j
& 1);
1177 if (p
->num_free_objects
>= num_objects
)
1181 /* Decrement the `GC context'. All objects allocated since the
1182 previous ggc_push_context are migrated to the outer context. */
1187 unsigned order
, depth
;
1189 depth
= --G
.context_depth
;
1191 /* Any remaining pages in the popped context are lowered to the new
1192 current context; i.e. objects allocated in the popped context and
1193 left over are imported into the previous context. */
1194 for (order
= 2; order
< NUM_ORDERS
; order
++)
1198 for (p
= G
.pages
[order
]; p
!= NULL
; p
= p
->next
)
1200 if (p
->context_depth
> depth
)
1201 p
->context_depth
= depth
;
1203 /* If this page is now in the topmost context, and we'd
1204 saved its allocation state, restore it. */
1205 else if (p
->context_depth
== depth
&& p
->save_in_use_p
)
1207 ggc_recalculate_in_use_p (p
);
1208 free (p
->save_in_use_p
);
1209 p
->save_in_use_p
= 0;
1215 /* Unmark all objects. */
1222 for (order
= 2; order
< NUM_ORDERS
; order
++)
1224 size_t num_objects
= OBJECTS_PER_PAGE (order
);
1225 size_t bitmap_size
= BITMAP_SIZE (num_objects
+ 1);
1228 for (p
= G
.pages
[order
]; p
!= NULL
; p
= p
->next
)
1230 #ifdef ENABLE_CHECKING
1231 /* The data should be page-aligned. */
1232 if ((size_t) p
->page
& (G
.pagesize
- 1))
1236 /* Pages that aren't in the topmost context are not collected;
1237 nevertheless, we need their in-use bit vectors to store GC
1238 marks. So, back them up first. */
1239 if (p
->context_depth
< G
.context_depth
)
1241 if (! p
->save_in_use_p
)
1242 p
->save_in_use_p
= xmalloc (bitmap_size
);
1243 memcpy (p
->save_in_use_p
, p
->in_use_p
, bitmap_size
);
1246 /* Reset reset the number of free objects and clear the
1247 in-use bits. These will be adjusted by mark_obj. */
1248 p
->num_free_objects
= num_objects
;
1249 memset (p
->in_use_p
, 0, bitmap_size
);
1251 /* Make sure the one-past-the-end bit is always set. */
1252 p
->in_use_p
[num_objects
/ HOST_BITS_PER_LONG
]
1253 = ((unsigned long) 1 << (num_objects
% HOST_BITS_PER_LONG
));
1258 /* Free all empty pages. Partially empty pages need no attention
1259 because the `mark' bit doubles as an `unused' bit. */
1266 for (order
= 2; order
< NUM_ORDERS
; order
++)
1268 /* The last page-entry to consider, regardless of entries
1269 placed at the end of the list. */
1270 page_entry
* const last
= G
.page_tails
[order
];
1272 size_t num_objects
= OBJECTS_PER_PAGE (order
);
1273 size_t live_objects
;
1274 page_entry
*p
, *previous
;
1284 page_entry
*next
= p
->next
;
1286 /* Loop until all entries have been examined. */
1289 /* Add all live objects on this page to the count of
1290 allocated memory. */
1291 live_objects
= num_objects
- p
->num_free_objects
;
1293 G
.allocated
+= OBJECT_SIZE (order
) * live_objects
;
1295 /* Only objects on pages in the topmost context should get
1297 if (p
->context_depth
< G
.context_depth
)
1300 /* Remove the page if it's empty. */
1301 else if (live_objects
== 0)
1304 G
.pages
[order
] = next
;
1306 previous
->next
= next
;
1308 /* Are we removing the last element? */
1309 if (p
== G
.page_tails
[order
])
1310 G
.page_tails
[order
] = previous
;
1315 /* If the page is full, move it to the end. */
1316 else if (p
->num_free_objects
== 0)
1318 /* Don't move it if it's already at the end. */
1319 if (p
!= G
.page_tails
[order
])
1321 /* Move p to the end of the list. */
1323 G
.page_tails
[order
]->next
= p
;
1325 /* Update the tail pointer... */
1326 G
.page_tails
[order
] = p
;
1328 /* ... and the head pointer, if necessary. */
1330 G
.pages
[order
] = next
;
1332 previous
->next
= next
;
1337 /* If we've fallen through to here, it's a page in the
1338 topmost context that is neither full nor empty. Such a
1339 page must precede pages at lesser context depth in the
1340 list, so move it to the head. */
1341 else if (p
!= G
.pages
[order
])
1343 previous
->next
= p
->next
;
1344 p
->next
= G
.pages
[order
];
1346 /* Are we moving the last element? */
1347 if (G
.page_tails
[order
] == p
)
1348 G
.page_tails
[order
] = previous
;
1357 /* Now, restore the in_use_p vectors for any pages from contexts
1358 other than the current one. */
1359 for (p
= G
.pages
[order
]; p
; p
= p
->next
)
1360 if (p
->context_depth
!= G
.context_depth
)
1361 ggc_recalculate_in_use_p (p
);
1366 /* Clobber all free objects. */
1373 for (order
= 2; order
< NUM_ORDERS
; order
++)
1375 size_t num_objects
= OBJECTS_PER_PAGE (order
);
1376 size_t size
= OBJECT_SIZE (order
);
1379 for (p
= G
.pages
[order
]; p
!= NULL
; p
= p
->next
)
1383 if (p
->context_depth
!= G
.context_depth
)
1384 /* Since we don't do any collection for pages in pushed
1385 contexts, there's no need to do any poisoning. And
1386 besides, the IN_USE_P array isn't valid until we pop
1390 for (i
= 0; i
< num_objects
; i
++)
1393 word
= i
/ HOST_BITS_PER_LONG
;
1394 bit
= i
% HOST_BITS_PER_LONG
;
1395 if (((p
->in_use_p
[word
] >> bit
) & 1) == 0)
1396 memset (p
->page
+ i
* size
, 0xa5, size
);
1403 /* Top level mark-and-sweep routine. */
1408 /* Avoid frequent unnecessary work by skipping collection if the
1409 total allocations haven't expanded much since the last
1411 #ifndef GGC_ALWAYS_COLLECT
1412 if (G
.allocated
< GGC_MIN_EXPAND_FOR_GC
* G
.allocated_last_gc
)
1416 timevar_push (TV_GC
);
1418 fprintf (stderr
, " {GC %luk -> ", (unsigned long) G
.allocated
/ 1024);
1420 /* Zero the total allocated bytes. This will be recalculated in the
1424 /* Release the pages we freed the last time we collected, but didn't
1425 reuse in the interim. */
1437 G
.allocated_last_gc
= G
.allocated
;
1438 if (G
.allocated_last_gc
< GGC_MIN_LAST_ALLOCATED
)
1439 G
.allocated_last_gc
= GGC_MIN_LAST_ALLOCATED
;
1441 timevar_pop (TV_GC
);
1444 fprintf (stderr
, "%luk}", (unsigned long) G
.allocated
/ 1024);
1447 /* Print allocation statistics. */
1448 #define SCALE(x) ((unsigned long) ((x) < 1024*10 \
1450 : ((x) < 1024*1024*10 \
1452 : (x) / (1024*1024))))
1453 #define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
1456 ggc_print_statistics ()
1458 struct ggc_statistics stats
;
1460 size_t total_overhead
= 0;
1462 /* Clear the statistics. */
1463 memset (&stats
, 0, sizeof (stats
));
1465 /* Make sure collection will really occur. */
1466 G
.allocated_last_gc
= 0;
1468 /* Collect and print the statistics common across collectors. */
1469 ggc_print_common_statistics (stderr
, &stats
);
1471 /* Release free pages so that we will not count the bytes allocated
1472 there as part of the total allocated memory. */
1475 /* Collect some information about the various sizes of
1477 fprintf (stderr
, "\n%-5s %10s %10s %10s\n",
1478 "Size", "Allocated", "Used", "Overhead");
1479 for (i
= 0; i
< NUM_ORDERS
; ++i
)
1486 /* Skip empty entries. */
1490 overhead
= allocated
= in_use
= 0;
1492 /* Figure out the total number of bytes allocated for objects of
1493 this size, and how many of them are actually in use. Also figure
1494 out how much memory the page table is using. */
1495 for (p
= G
.pages
[i
]; p
; p
= p
->next
)
1497 allocated
+= p
->bytes
;
1499 (OBJECTS_PER_PAGE (i
) - p
->num_free_objects
) * OBJECT_SIZE (i
);
1501 overhead
+= (sizeof (page_entry
) - sizeof (long)
1502 + BITMAP_SIZE (OBJECTS_PER_PAGE (i
) + 1));
1504 fprintf (stderr
, "%-5d %10ld%c %10ld%c %10ld%c\n", OBJECT_SIZE (i
),
1505 SCALE (allocated
), LABEL (allocated
),
1506 SCALE (in_use
), LABEL (in_use
),
1507 SCALE (overhead
), LABEL (overhead
));
1508 total_overhead
+= overhead
;
1510 fprintf (stderr
, "%-5s %10ld%c %10ld%c %10ld%c\n", "Total",
1511 SCALE (G
.bytes_mapped
), LABEL (G
.bytes_mapped
),
1512 SCALE (G
.allocated
), LABEL(G
.allocated
),
1513 SCALE (total_overhead
), LABEL (total_overhead
));