2 * sgen-gc.c: Simple generational GC.
5 * Paolo Molaro (lupus@ximian.com)
7 * Copyright 2005-2010 Novell, Inc (http://www.novell.com)
9 * Thread start/stop adapted from Boehm's GC:
10 * Copyright (c) 1994 by Xerox Corporation. All rights reserved.
11 * Copyright (c) 1996 by Silicon Graphics. All rights reserved.
12 * Copyright (c) 1998 by Fergus Henderson. All rights reserved.
13 * Copyright (c) 2000-2004 by Hewlett-Packard Company. All rights reserved.
15 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
16 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
18 * Permission is hereby granted to use or copy this program
19 * for any purpose, provided the above notices are retained on all copies.
20 * Permission to modify the code and to distribute modified code is granted,
21 * provided the above notices are retained, and a notice that the code was
22 * modified is included with the above copyright notice.
25 * Copyright 2001-2003 Ximian, Inc
26 * Copyright 2003-2010 Novell, Inc.
28 * Permission is hereby granted, free of charge, to any person obtaining
29 * a copy of this software and associated documentation files (the
30 * "Software"), to deal in the Software without restriction, including
31 * without limitation the rights to use, copy, modify, merge, publish,
32 * distribute, sublicense, and/or sell copies of the Software, and to
33 * permit persons to whom the Software is furnished to do so, subject to
34 * the following conditions:
36 * The above copyright notice and this permission notice shall be
37 * included in all copies or substantial portions of the Software.
39 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
40 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
41 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
42 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
43 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
44 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
45 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
50 #include "utils/mono-counters.h"
51 #include "metadata/sgen-gc.h"
53 /* Pinned objects are allocated in the LOS space if bigger than half a page
54 * or from freelists otherwise. We assume that pinned objects are relatively few
55 * and they have a slow dying speed (like interned strings, thread objects).
56 * As such they will be collected only at major collections.
57 * free lists are not global: when we need memory we allocate a PinnedChunk.
58 * Each pinned chunk is made of several pages, the first of wich is used
59 * internally for bookeeping (here think of a page as 4KB). The bookeeping
60 * includes the freelists vectors and info about the object size of each page
61 * in the pinned chunk. So, when needed, a free page is found in a pinned chunk,
62 * a size is assigned to it, the page is divided in the proper chunks and each
63 * chunk is added to the freelist. To not waste space, the remaining space in the
64 * first page is used as objects of size 16 or 32 (need to measure which are more
66 * We use this same structure to allocate memory used internally by the GC, so
67 * we never use malloc/free if we need to alloc during collection: the world is stopped
68 * and malloc/free will deadlock.
69 * When we want to iterate over pinned objects, we just scan a page at a time
70 * linearly according to the size of objects in the page: the next pointer used to link
71 * the items in the freelist uses the same word as the vtable. Since we keep freelists
72 * for each pinned chunk, if the word points outside the pinned chunk it means
74 * We could avoid this expensive scanning in creative ways. We could have a policy
75 * of putting in the pinned space only objects we know about that have no struct fields
76 * with references and we can easily use a even expensive write barrier for them,
77 * since pointer writes on such objects should be rare.
78 * The best compromise is to just alloc interned strings and System.MonoType in them.
79 * It would be nice to allocate MonoThread in it, too: must check that we properly
80 * use write barriers so we don't have to do any expensive scanning of the whole pinned
81 * chunk list during minor collections. We can avoid it now because we alloc in it only
82 * reference-free objects.
84 struct _SgenPinnedChunk {
87 SgenInternalAllocator *allocator;
88 int *page_sizes; /* a 0 means the page is still unused */
90 SgenPinnedChunk *free_list_nexts [SGEN_INTERNAL_FREELIST_NUM_SLOTS];
92 void *data [1]; /* page sizes and free lists are stored here */
95 #define PINNED_FIRST_SLOT_SIZE (sizeof (gpointer) * 4)
96 #define MAX_FREELIST_SIZE 8192
98 /* This is a fixed value used for pinned chunks, not the system pagesize */
99 #define FREELIST_PAGESIZE (16*1024)
101 /* keep each size a multiple of ALLOC_ALIGN */
102 /* on 64 bit systems 8 is likely completely unused. */
103 static const int freelist_sizes [] = {
104 8, 16, 24, 32, 40, 48, 64, 80,
105 96, 128, 160, 192, 224, 256, 320, 384,
106 448, 512, 584, 680, 816, 1024, 1360, 2048,
107 2336, 2728, 3272, 4096, 5456, 8192 };
110 * Slot indexes for the fixed INTERNAL_MEM_XXX types. -1 if that type
113 static int fixed_type_freelist_slots [INTERNAL_MEM_MAX];
115 static SgenInternalAllocator unmanaged_allocator;
117 #define LARGE_INTERNAL_MEM_HEADER_MAGIC 0x7d289f3a
119 typedef struct _LargeInternalMemHeader LargeInternalMemHeader;
120 struct _LargeInternalMemHeader {
126 static long long pinned_chunk_bytes_alloced = 0;
127 static long long large_internal_bytes_alloced = 0;
129 #ifdef HEAVY_STATISTICS
130 static long long stat_internal_alloc = 0;
137 report_pinned_chunk (SgenPinnedChunk *chunk, int seq) {
139 int i, free_pages, num_free, free_mem;
141 for (i = 0; i < chunk->num_pages; ++i) {
142 if (!chunk->page_sizes [i])
145 printf ("Pinned chunk %d at %p, size: %d, pages: %d, free: %d\n", seq, chunk, chunk->num_pages * FREELIST_PAGESIZE, chunk->num_pages, free_pages);
146 free_mem = FREELIST_PAGESIZE * free_pages;
147 for (i = 0; i < SGEN_INTERNAL_FREELIST_NUM_SLOTS; ++i) {
148 if (!chunk->free_list [i])
151 p = chunk->free_list [i];
156 printf ("\tfree list of size %d, %d items\n", freelist_sizes [i], num_free);
157 free_mem += freelist_sizes [i] * num_free;
159 printf ("\tfree memory in chunk: %d\n", free_mem);
166 mono_sgen_report_internal_mem_usage_full (SgenInternalAllocator *alc)
168 SgenPinnedChunk *chunk;
170 for (chunk = alc->chunk_list; chunk; chunk = chunk->block.next)
171 report_pinned_chunk (chunk, i++);
175 mono_sgen_report_internal_mem_usage (void)
177 mono_sgen_report_internal_mem_usage_full (&unmanaged_allocator);
181 * Find the slot number in the freelist for memory chunks that
182 * can contain @size objects.
185 slot_for_size (size_t size)
188 /* do a binary search or lookup table later. */
189 for (slot = 0; slot < SGEN_INTERNAL_FREELIST_NUM_SLOTS; ++slot) {
190 if (freelist_sizes [slot] >= size)
193 g_assert_not_reached ();
198 mono_sgen_register_fixed_internal_mem_type (int type, size_t size)
202 g_assert (type >= 0 && type < INTERNAL_MEM_MAX);
203 g_assert (fixed_type_freelist_slots [type] == -1);
205 slot = slot_for_size (size);
206 g_assert (slot >= 0);
208 fixed_type_freelist_slots [type] = slot;
212 * Build a free list for @size memory chunks from the memory area between
213 * start_page and end_page.
216 build_freelist (SgenInternalAllocator *alc, SgenPinnedChunk *chunk, int slot, int size, char *start_page, char *end_page)
220 /*g_print ("building freelist for slot %d, size %d in %p\n", slot, size, chunk);*/
221 p = (void**)start_page;
222 end = (void**)(end_page - size);
223 g_assert (!chunk->free_list [slot]);
224 chunk->free_list [slot] = p;
225 while ((char*)p + size <= (char*)end) {
227 *p = (void*)((char*)p + size);
231 /*g_print ("%d items created, max: %d\n", count, (end_page - start_page) / size);*/
233 g_assert (!chunk->free_list_nexts [slot]);
234 chunk->free_list_nexts [slot] = alc->free_lists [slot];
235 alc->free_lists [slot] = chunk;
238 static SgenPinnedChunk*
239 alloc_pinned_chunk (SgenInternalAllocator *alc, gboolean managed)
241 SgenPinnedChunk *chunk;
243 int size = SGEN_PINNED_CHUNK_SIZE;
245 chunk = mono_sgen_alloc_os_memory_aligned (size, size, TRUE);
246 chunk->block.role = managed ? MEMORY_ROLE_PINNED : MEMORY_ROLE_INTERNAL;
249 mono_sgen_update_heap_boundaries ((mword)chunk, ((mword)chunk + size));
251 pinned_chunk_bytes_alloced += size;
253 /* setup the bookeeping fields */
254 chunk->num_pages = size / FREELIST_PAGESIZE;
255 offset = G_STRUCT_OFFSET (SgenPinnedChunk, data);
256 chunk->page_sizes = (void*)((char*)chunk + offset);
257 offset += sizeof (int) * chunk->num_pages;
258 offset = SGEN_ALIGN_UP (offset);
259 chunk->free_list = (void*)((char*)chunk + offset);
260 offset += sizeof (void*) * SGEN_INTERNAL_FREELIST_NUM_SLOTS;
261 offset = SGEN_ALIGN_UP (offset);
262 chunk->start_data = (void*)((char*)chunk + offset);
264 /* allocate the first page to the freelist */
265 chunk->page_sizes [0] = PINNED_FIRST_SLOT_SIZE;
266 build_freelist (alc, chunk, slot_for_size (PINNED_FIRST_SLOT_SIZE), PINNED_FIRST_SLOT_SIZE,
267 chunk->start_data, ((char*)chunk + FREELIST_PAGESIZE));
268 mono_sgen_debug_printf (4, "Allocated pinned chunk %p, size: %d\n", chunk, size);
270 chunk->block.next = alc->chunk_list;
271 alc->chunk_list = chunk;
273 chunk->allocator = alc;
278 /* Must be called with an empty freelist for the given slot. */
280 populate_chunk_page (SgenInternalAllocator *alc, SgenPinnedChunk *chunk, int slot)
282 int size = freelist_sizes [slot];
284 g_assert (!chunk->free_list [slot]);
285 g_assert (!chunk->free_list_nexts [slot]);
286 for (i = 0; i < chunk->num_pages; ++i) {
287 if (chunk->page_sizes [i])
289 chunk->page_sizes [i] = size;
290 build_freelist (alc, chunk, slot, size, (char*)chunk + FREELIST_PAGESIZE * i, (char*)chunk + FREELIST_PAGESIZE * (i + 1));
297 alloc_from_slot (SgenInternalAllocator *alc, int slot, int type)
299 SgenPinnedChunk *pchunk;
300 size_t size = freelist_sizes [slot];
302 alc->small_internal_mem_bytes [type] += size;
304 if (alc->delayed_free_lists [slot]) {
307 p = alc->delayed_free_lists [slot];
308 } while (SGEN_CAS_PTR (&alc->delayed_free_lists [slot], *p, p) != p);
314 pchunk = alc->free_lists [slot];
316 void **p = pchunk->free_list [slot];
322 pchunk->free_list [slot] = next;
325 alc->free_lists [slot] = pchunk->free_list_nexts [slot];
326 pchunk->free_list_nexts [slot] = NULL;
333 for (pchunk = alc->chunk_list; pchunk; pchunk = pchunk->block.next) {
334 if (populate_chunk_page (alc, pchunk, slot))
338 pchunk = alloc_pinned_chunk (alc, type == INTERNAL_MEM_MANAGED);
339 /* FIXME: handle OOM */
340 if (pchunk->free_list [slot])
342 if (!populate_chunk_page (alc, pchunk, slot))
343 g_assert_not_reached ();
347 /* used for the GC-internal data structures */
349 mono_sgen_alloc_internal_full (SgenInternalAllocator *alc, size_t size, int type)
354 g_assert (fixed_type_freelist_slots [type] == -1);
356 HEAVY_STAT (++stat_internal_alloc);
358 if (size > freelist_sizes [SGEN_INTERNAL_FREELIST_NUM_SLOTS - 1]) {
359 LargeInternalMemHeader *mh;
361 size += sizeof (LargeInternalMemHeader);
362 mh = mono_sgen_alloc_os_memory (size, TRUE);
363 mh->magic = LARGE_INTERNAL_MEM_HEADER_MAGIC;
365 /* FIXME: do a CAS here */
366 large_internal_bytes_alloced += size;
370 slot = slot_for_size (size);
371 g_assert (size <= freelist_sizes [slot]);
372 res = alloc_from_slot (alc, slot, type);
378 mono_sgen_alloc_internal_fixed (SgenInternalAllocator *allocator, int type)
380 int slot = fixed_type_freelist_slots [type];
381 g_assert (slot >= 0);
382 return alloc_from_slot (allocator, slot, type);
386 mono_sgen_alloc_internal (int type)
388 return mono_sgen_alloc_internal_fixed (&unmanaged_allocator, type);
392 mono_sgen_alloc_internal_dynamic (size_t size, int type)
394 return mono_sgen_alloc_internal_full (&unmanaged_allocator, size, type);
398 free_from_slot (SgenInternalAllocator *alc, void *addr, int slot, int type)
400 SgenPinnedChunk *pchunk = (SgenPinnedChunk*)SGEN_PINNED_CHUNK_FOR_PTR (addr);
404 g_assert (addr >= (void*)pchunk && (char*)addr < (char*)pchunk + pchunk->num_pages * FREELIST_PAGESIZE);
405 if (type == INTERNAL_MEM_MANAGED)
406 g_assert (pchunk->block.role == MEMORY_ROLE_PINNED);
408 g_assert (pchunk->block.role == MEMORY_ROLE_INTERNAL);
410 next = pchunk->free_list [slot];
412 pchunk->free_list [slot] = p;
415 g_assert (!pchunk->free_list_nexts [slot]);
416 pchunk->free_list_nexts [slot] = alc->free_lists [slot];
417 alc->free_lists [slot] = pchunk;
420 alc->small_internal_mem_bytes [type] -= freelist_sizes [slot];
424 mono_sgen_free_internal_full (SgenInternalAllocator *alc, void *addr, size_t size, int type)
426 LargeInternalMemHeader *mh;
428 g_assert (fixed_type_freelist_slots [type] == -1);
433 if (size <= freelist_sizes [SGEN_INTERNAL_FREELIST_NUM_SLOTS - 1]) {
434 int slot = slot_for_size (size);
435 free_from_slot (alc, addr, slot, type);
439 mh = (LargeInternalMemHeader*)((char*)addr - G_STRUCT_OFFSET (LargeInternalMemHeader, data));
440 g_assert (mh->magic == LARGE_INTERNAL_MEM_HEADER_MAGIC);
441 g_assert (mh->size == size + sizeof (LargeInternalMemHeader));
442 /* FIXME: do a CAS */
443 large_internal_bytes_alloced -= mh->size;
444 mono_sgen_free_os_memory (mh, mh->size);
448 mono_sgen_free_internal_fixed (SgenInternalAllocator *allocator, void *addr, int type)
450 int slot = fixed_type_freelist_slots [type];
451 g_assert (slot >= 0);
453 free_from_slot (allocator, addr, slot, type);
457 mono_sgen_free_internal (void *addr, int type)
459 mono_sgen_free_internal_fixed (&unmanaged_allocator, addr, type);
463 mono_sgen_free_internal_dynamic (void *addr, size_t size, int type)
465 mono_sgen_free_internal_full (&unmanaged_allocator, addr, size, type);
469 mono_sgen_free_internal_delayed (void *addr, int type, SgenInternalAllocator *thread_allocator)
471 SgenPinnedChunk *pchunk = (SgenPinnedChunk*)SGEN_PINNED_CHUNK_FOR_PTR (addr);
472 SgenInternalAllocator *alc = pchunk->allocator;
476 if (alc == thread_allocator) {
477 mono_sgen_free_internal_fixed (alc, addr, type);
481 slot = fixed_type_freelist_slots [type];
482 g_assert (slot >= 0);
485 next = alc->delayed_free_lists [slot];
486 *(void**)addr = next;
487 } while (SGEN_CAS_PTR (&alc->delayed_free_lists [slot], addr, next) != next);
491 mono_sgen_dump_internal_mem_usage (FILE *heap_dump_file)
493 static char const *internal_mem_names [] = { "managed", "pin-queue", "fragment", "section", "scan-starts",
494 "fin-table", "finalize-entry", "dislink-table",
495 "dislink", "roots-table", "root-record", "statistics",
496 "remset", "gray-queue", "store-remset", "marksweep-tables",
497 "marksweep-block-info", "ephemeron-link" };
501 fprintf (heap_dump_file, "<other-mem-usage type=\"large-internal\" size=\"%lld\"/>\n", large_internal_bytes_alloced);
502 fprintf (heap_dump_file, "<other-mem-usage type=\"pinned-chunks\" size=\"%lld\"/>\n", pinned_chunk_bytes_alloced);
503 for (i = 0; i < INTERNAL_MEM_MAX; ++i) {
504 fprintf (heap_dump_file, "<other-mem-usage type=\"%s\" size=\"%ld\"/>\n",
505 internal_mem_names [i], unmanaged_allocator.small_internal_mem_bytes [i]);
510 mono_sgen_init_internal_allocator (void)
514 g_assert (SGEN_INTERNAL_FREELIST_NUM_SLOTS == sizeof (freelist_sizes) / sizeof (freelist_sizes [0]));
516 for (i = 0; i < INTERNAL_MEM_MAX; ++i)
517 fixed_type_freelist_slots [i] = -1;
519 #ifdef HEAVY_STATISTICS
520 mono_counters_register ("Internal allocs", MONO_COUNTER_GC | MONO_COUNTER_LONG, &stat_internal_alloc);
524 SgenInternalAllocator*
525 mono_sgen_get_unmanaged_allocator (void)
527 return &unmanaged_allocator;
531 mono_sgen_internal_scan_objects (SgenInternalAllocator *alc, IterateObjectCallbackFunc callback, void *callback_data)
533 SgenPinnedChunk *chunk;
538 for (chunk = alc->chunk_list; chunk; chunk = chunk->block.next) {
539 end_chunk = (char*)chunk + chunk->num_pages * FREELIST_PAGESIZE;
540 mono_sgen_debug_printf (6, "Scanning pinned chunk %p (range: %p-%p)\n", chunk, chunk->start_data, end_chunk);
541 for (i = 0; i < chunk->num_pages; ++i) {
542 obj_size = chunk->page_sizes [i];
545 p = i? (char*)chunk + i * FREELIST_PAGESIZE: chunk->start_data;
546 endp = i? p + FREELIST_PAGESIZE: (char*)chunk + FREELIST_PAGESIZE;
547 mono_sgen_debug_printf (6, "Page %d (size: %d, range: %p-%p)\n", i, obj_size, p, endp);
548 while (p + obj_size <= endp) {
550 /* if the first word (the vtable) is outside the chunk we have an object */
551 if (*ptr && (*ptr < (void*)chunk || *ptr >= end_chunk))
552 callback ((char*)ptr, obj_size, callback_data);
560 mono_sgen_internal_update_heap_boundaries (SgenInternalAllocator *alc)
562 SgenPinnedChunk *chunk;
563 for (chunk = alc->chunk_list; chunk; chunk = chunk->block.next) {
564 char *end_chunk = (char*)chunk + chunk->num_pages * FREELIST_PAGESIZE;
565 mono_sgen_update_heap_boundaries ((mword)chunk, (mword)end_chunk);
570 * the array of pointers from @start to @end contains conservative
571 * pointers to objects inside @chunk: mark each referenced object
575 mark_pinned_from_addresses (SgenPinnedChunk *chunk, void **start, void **end, IterateObjectCallbackFunc callback, void *callback_data)
577 for (; start < end; start++) {
579 int offset = (char*)addr - (char*)chunk;
580 int page = offset / FREELIST_PAGESIZE;
581 int obj_offset = page == 0? offset - ((char*)chunk->start_data - (char*)chunk): offset % FREELIST_PAGESIZE;
582 int slot_size = chunk->page_sizes [page];
584 /* the page is not allocated */
587 /* would be faster if we restrict the sizes to power of two,
588 * but that's a waste of memory: need to measure. it could reduce
589 * fragmentation since there are less pages needed, if for example
590 * someone interns strings of each size we end up with one page per
591 * interned string (still this is just ~40 KB): with more fine-grained sizes
592 * this increases the number of used pages.
595 obj_offset /= slot_size;
596 obj_offset *= slot_size;
597 addr = (char*)chunk->start_data + obj_offset;
599 obj_offset /= slot_size;
600 obj_offset *= slot_size;
601 addr = (char*)chunk + page * FREELIST_PAGESIZE + obj_offset;
604 /* if the vtable is inside the chunk it's on the freelist, so skip */
605 /* FIXME: is it possible that we're pinning objects more than once here? */
606 if (*ptr && (*ptr < (void*)chunk->start_data || *ptr > (void*)((char*)chunk + chunk->num_pages * FREELIST_PAGESIZE)))
607 callback (addr, slot_size, callback_data);
612 mono_sgen_internal_scan_pinned_objects (SgenInternalAllocator *alc, IterateObjectCallbackFunc callback, void *callback_data)
614 SgenPinnedChunk *chunk;
616 /* look for pinned addresses for pinned-alloc objects */
617 mono_sgen_debug_printf (6, "Pinning from pinned-alloc objects\n");
618 for (chunk = alc->chunk_list; chunk; chunk = chunk->block.next) {
620 void **pinned = mono_sgen_find_optimized_pin_queue_area (chunk->start_data,
621 (char*)chunk + chunk->num_pages * FREELIST_PAGESIZE, &num_pinned);
623 mark_pinned_from_addresses (chunk, pinned, pinned + num_pinned, callback, callback_data);