2 * sgen-splliy-nursery.c: 3-space based nursery collector.
5 * Rodrigo Kumpera Kumpera <kumpera@gmail.com>
7 * Copyright 2001-2003 Ximian, Inc
8 * Copyright 2003-2010 Novell, Inc.
9 * Copyright 2011-2012 Xamarin Inc (http://www.xamarin.com)
10 * Copyright (C) 2012 Xamarin Inc
12 * This library is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU Library General Public
14 * License 2.0 as published by the Free Software Foundation;
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Library General Public License for more details.
21 * You should have received a copy of the GNU Library General Public
22 * License 2.0 along with this library; if not, write to the Free
23 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
29 #include "metadata/profiler-private.h"
31 #include "metadata/sgen-gc.h"
32 #include "metadata/sgen-protocol.h"
33 #include "metadata/sgen-layout-stats.h"
34 #include "utils/mono-memory-model.h"
37 The nursery is logically divided into 3 spaces: Allocator space and two Survivor spaces.
39 Objects are born (allocated by the mutator) in the Allocator Space.
41 The Survivor spaces are divided in a copying collector style From and To spaces.
42 The hole of each space switch on each collection.
44 On each collection we process objects from the nursery this way:
45 Objects from the Allocator Space are evacuated into the To Space.
46 Objects from the Survivor From Space are evacuated into the old generation.
49 The nursery is physically divided in two parts, set by the promotion barrier.
51 The Allocator Space takes the botton part of the nursery.
53 The Survivor spaces are intermingled in the top part of the nursery. It's done
54 this way since the required size for the To Space depends on the survivor rate
55 of objects from the Allocator Space.
57 During a collection when the object scan function see a nursery object it must
58 determine if the object needs to be evacuated or left in place. Originally, this
59 check was done by checking if a forwarding pointer is installed, but now an object
60 can be in the To Space, it won't have a forwarding pointer and it must be left in place.
62 In order to solve that we classify nursery memory been either in the From Space or in
63 the To Space. Since the Allocator Space has the same behavior as the Survivor From Space
64 they are unified for this purpoise - a bit confusing at first.
66 This from/to classification is done on a larger granule than object to make the check efficient
67 and, due to that, we must make sure that all fragemnts used to allocate memory from the To Space
68 are naturally aligned in both ends to that granule to avoid wronly classifying a From Space object.
71 -The promotion barrier is statically defined to 50% of the nursery, it should be dinamically adjusted based
73 -We apply the same promotion policy to all objects, finalizable ones should age longer in the nursery;
74 -We apply the same promotion policy to all stages of a collection, maybe we should promote more aggressively
75 objects from non-stack roots, specially those found in the remembered set;
76 -Fix our major collection trigger to happen before we do a minor GC and collect the nursery only once.
77 -Make the serial fragment allocator fast path inlineable
78 -Make aging threshold be based on survival rates and survivor occupancy;
79 -Change promotion barrier to be size and not address based;
80 -Pre allocate memory for young ages to make sure that on overflow only the older suffer;
81 -Get rid of par_alloc_buffer_refill_mutex so to the parallel collection of the nursery doesn't suck;
84 /*FIXME Move this to a separate header. */
85 #define _toi(ptr) ((size_t)ptr)
86 #define make_ptr_mask(bits) ((1 << bits) - 1)
87 #define align_down(ptr, bits) ((void*)(_toi(ptr) & ~make_ptr_mask (bits)))
88 #define align_up(ptr, bits) ((void*) ((_toi(ptr) + make_ptr_mask (bits)) & ~make_ptr_mask (bits)))
91 Even though the effective max age is 255, aging that much doesn't make sense.
92 It might even make sense to use nimbles for age recording.
97 * Each age has its allocation buffer. Whenever an object is to be
98 * aged we try to fit it into its new age's allocation buffer. If
99 * that is not possible we get new space from the fragment allocator
100 * and set the allocation buffer to that space (minus the space
101 * required for the object).
107 } AgeAllocationBuffer;
109 /* Limits the ammount of memory the mutator can have. */
110 static char *promotion_barrier;
113 Promotion age and alloc ratio are the two nursery knobs to control
114 how much effort we want to spend on young objects.
116 Allocation ratio should be the inverse of the expected survivor rate.
117 The more objects surviver, the smaller the alloc ratio much be so we can
120 Promote age depends on how much effort we want to spend aging objects before
121 we promote them to the old generation. If addional ages don't somewhat improve
122 mortality, it's better avoid as they increase the cost of minor collections.
128 If we're evacuating an object with this age or more, promote it.
129 Age is the number of surviving collections of an object.
131 static int promote_age = 2;
134 Initial ratio of allocation and survivor spaces.
135 This should be read as the fraction of the whole nursery dedicated
136 for the allocator space.
138 static float alloc_ratio = 60.f/100.f;
141 static char *region_age;
142 static int region_age_size;
143 static AgeAllocationBuffer age_alloc_buffers [MAX_AGE];
145 /* The collector allocs from here. */
146 static SgenFragmentAllocator collector_allocator;
148 static LOCK_DECLARE (par_alloc_buffer_refill_mutex);
151 get_object_age (char *object)
153 int idx = (object - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
154 return region_age [idx];
158 set_object_age (char *object, int age)
160 int idx = (object - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
161 region_age [idx] = age;
165 set_age_in_range (char *start, char *end, int age)
168 int region_idx, length;
169 region_idx = (start - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
170 region_start = ®ion_age [region_idx];
171 length = (end - start) >> SGEN_TO_SPACE_GRANULE_BITS;
172 memset (region_start, age, length);
176 mark_bit (char *space_bitmap, char *pos)
178 int idx = (pos - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
182 g_assert (byte < sgen_space_bitmap_size);
183 space_bitmap [byte] |= 1 << bit;
187 mark_bits_in_range (char *space_bitmap, char *start, char *end)
189 start = align_down (start, SGEN_TO_SPACE_GRANULE_BITS);
190 end = align_up (end, SGEN_TO_SPACE_GRANULE_BITS);
192 for (;start < end; start += SGEN_TO_SPACE_GRANULE_IN_BYTES)
193 mark_bit (space_bitmap, start);
197 * This splits the fragments at the point of the promotion barrier.
198 * Two allocator are actually involved here: The mutator allocator and
199 * the collector allocator. This function is called with the
200 * collector, but it's a copy of the mutator allocator and contains
201 * all the fragments in the nursery. The fragments below the
202 * promotion barrier are left with the mutator allocator and the ones
203 * above are put into the collector allocator.
206 fragment_list_split (SgenFragmentAllocator *allocator)
208 SgenFragment *prev = NULL, *list = allocator->region_head;
211 if (list->fragment_end > promotion_barrier) {
212 if (list->fragment_start < promotion_barrier) {
213 SgenFragment *res = sgen_fragment_allocator_alloc ();
215 res->fragment_start = promotion_barrier;
216 res->fragment_next = promotion_barrier;
217 res->fragment_end = list->fragment_end;
218 res->next = list->next;
219 res->next_in_order = list->next_in_order;
220 g_assert (res->fragment_end > res->fragment_start);
222 list->fragment_end = promotion_barrier;
223 list->next = list->next_in_order = NULL;
224 set_age_in_range (list->fragment_start, list->fragment_end, 0);
226 allocator->region_head = allocator->alloc_head = res;
230 prev->next = prev->next_in_order = NULL;
231 allocator->region_head = allocator->alloc_head = list;
235 set_age_in_range (list->fragment_start, list->fragment_end, 0);
239 allocator->region_head = allocator->alloc_head = NULL;
242 /******************************************Minor Collector API ************************************************/
244 #define AGE_ALLOC_BUFFER_MIN_SIZE SGEN_TO_SPACE_GRANULE_IN_BYTES
245 #define AGE_ALLOC_BUFFER_DESIRED_SIZE (SGEN_TO_SPACE_GRANULE_IN_BYTES * 8)
248 alloc_for_promotion_slow_path (int age, size_t objsize)
251 size_t allocated_size;
252 size_t aligned_objsize = (size_t)align_up (objsize, SGEN_TO_SPACE_GRANULE_BITS);
254 p = sgen_fragment_allocator_serial_range_alloc (
255 &collector_allocator,
256 MAX (aligned_objsize, AGE_ALLOC_BUFFER_DESIRED_SIZE),
257 MAX (aligned_objsize, AGE_ALLOC_BUFFER_MIN_SIZE),
260 set_age_in_range (p, p + allocated_size, age);
261 sgen_clear_range (age_alloc_buffers [age].next, age_alloc_buffers [age].end);
262 age_alloc_buffers [age].next = p + objsize;
263 age_alloc_buffers [age].end = p + allocated_size;
269 alloc_for_promotion (MonoVTable *vtable, char *obj, size_t objsize, gboolean has_references)
274 age = get_object_age (obj);
275 if (age >= promote_age)
276 return major_collector.alloc_object (vtable, objsize, has_references);
281 p = age_alloc_buffers [age].next;
282 if (G_LIKELY (p + objsize <= age_alloc_buffers [age].end)) {
283 age_alloc_buffers [age].next += objsize;
285 p = alloc_for_promotion_slow_path (age, objsize);
287 return major_collector.alloc_object (vtable, objsize, has_references);
290 *(MonoVTable**)p = vtable;
296 par_alloc_for_promotion_slow_path (int age, size_t objsize)
299 size_t allocated_size;
300 size_t aligned_objsize = (size_t)align_up (objsize, SGEN_TO_SPACE_GRANULE_BITS);
302 mono_mutex_lock (&par_alloc_buffer_refill_mutex);
305 p = age_alloc_buffers [age].next;
306 if (G_LIKELY (p + objsize <= age_alloc_buffers [age].end)) {
307 if (SGEN_CAS_PTR ((void*)&age_alloc_buffers [age].next, p + objsize, p) != p)
310 /* Reclaim remaining space - if we OOMd the nursery nothing to see here. */
311 char *end = age_alloc_buffers [age].end;
314 p = age_alloc_buffers [age].next;
315 } while (SGEN_CAS_PTR ((void*)&age_alloc_buffers [age].next, end, p) != p);
316 sgen_clear_range (p, end);
319 /* By setting end to NULL we make sure no other thread can advance while we're updating.*/
320 age_alloc_buffers [age].end = NULL;
323 p = sgen_fragment_allocator_par_range_alloc (
324 &collector_allocator,
325 MAX (aligned_objsize, AGE_ALLOC_BUFFER_DESIRED_SIZE),
326 MAX (aligned_objsize, AGE_ALLOC_BUFFER_MIN_SIZE),
329 set_age_in_range (p, p + allocated_size, age);
330 age_alloc_buffers [age].next = p + objsize;
331 STORE_STORE_FENCE; /* Next must arrive before the new value for next. */
332 age_alloc_buffers [age].end = p + allocated_size;
336 mono_mutex_unlock (&par_alloc_buffer_refill_mutex);
341 par_alloc_for_promotion (MonoVTable *vtable, char *obj, size_t objsize, gboolean has_references)
346 age = get_object_age (obj);
347 if (age >= promote_age)
348 return major_collector.par_alloc_object (vtable, objsize, has_references);
351 p = age_alloc_buffers [age].next;
353 LOAD_LOAD_FENCE; /* The read of ->next must happen before ->end */
355 if (G_LIKELY (p + objsize <= age_alloc_buffers [age].end)) {
356 if (SGEN_CAS_PTR ((void*)&age_alloc_buffers [age].next, p + objsize, p) != p)
359 p = par_alloc_for_promotion_slow_path (age, objsize);
361 /* Have we failed to promote to the nursery, lets just evacuate it to old gen. */
363 return major_collector.par_alloc_object (vtable, objsize, has_references);
366 *(MonoVTable**)p = vtable;
372 minor_alloc_for_promotion (MonoVTable *vtable, char *obj, size_t objsize, gboolean has_references)
375 We only need to check for a non-nursery object if we're doing a major collection.
377 if (!sgen_ptr_in_nursery (obj))
378 return major_collector.alloc_object (vtable, objsize, has_references);
380 return alloc_for_promotion (vtable, obj, objsize, has_references);
384 minor_par_alloc_for_promotion (MonoVTable *vtable, char *obj, size_t objsize, gboolean has_references)
387 We only need to check for a non-nursery object if we're doing a major collection.
389 if (!sgen_ptr_in_nursery (obj))
390 return major_collector.par_alloc_object (vtable, objsize, has_references);
392 return par_alloc_for_promotion (vtable, obj, objsize, has_references);
396 build_fragments_get_exclude_head (void)
399 for (i = 0; i < MAX_AGE; ++i) {
400 /*If we OOM'd on the last collection ->end might be null while ->next not.*/
401 if (age_alloc_buffers [i].end)
402 sgen_clear_range (age_alloc_buffers [i].next, age_alloc_buffers [i].end);
405 return collector_allocator.region_head;
409 build_fragments_release_exclude_head (void)
411 sgen_fragment_allocator_release (&collector_allocator);
415 build_fragments_finish (SgenFragmentAllocator *allocator)
417 /* We split the fragment list based on the promotion barrier. */
418 collector_allocator = *allocator;
419 fragment_list_split (&collector_allocator);
423 prepare_to_space (char *to_space_bitmap, int space_bitmap_size)
425 SgenFragment **previous, *frag;
427 memset (to_space_bitmap, 0, space_bitmap_size);
428 memset (age_alloc_buffers, 0, sizeof (age_alloc_buffers));
430 previous = &collector_allocator.alloc_head;
432 for (frag = *previous; frag; frag = *previous) {
433 char *start = align_up (frag->fragment_next, SGEN_TO_SPACE_GRANULE_BITS);
434 char *end = align_down (frag->fragment_end, SGEN_TO_SPACE_GRANULE_BITS);
436 /* Fragment is too small to be usable. */
437 if ((end - start) < SGEN_MAX_NURSERY_WASTE) {
438 sgen_clear_range (frag->fragment_next, frag->fragment_end);
439 frag->fragment_next = frag->fragment_end = frag->fragment_start;
440 *previous = frag->next;
445 We need to insert 3 phony objects so the fragments build step can correctly
449 /* Clean the fragment range. */
450 sgen_clear_range (start, end);
451 /* We need a phony object in between the original fragment start and the effective one. */
452 if (start != frag->fragment_next)
453 sgen_clear_range (frag->fragment_next, start);
454 /* We need an phony object in between the new fragment end and the original fragment end. */
455 if (end != frag->fragment_end)
456 sgen_clear_range (end, frag->fragment_end);
458 frag->fragment_start = frag->fragment_next = start;
459 frag->fragment_end = end;
460 mark_bits_in_range (to_space_bitmap, start, end);
461 previous = &frag->next;
466 clear_fragments (void)
468 sgen_clear_allocator_fragments (&collector_allocator);
472 init_nursery (SgenFragmentAllocator *allocator, char *start, char *end)
474 int alloc_quote = (int)((end - start) * alloc_ratio);
475 promotion_barrier = align_down (start + alloc_quote, 3);
476 sgen_fragment_allocator_add (allocator, start, promotion_barrier);
477 sgen_fragment_allocator_add (&collector_allocator, promotion_barrier, end);
479 region_age_size = (end - start) >> SGEN_TO_SPACE_GRANULE_BITS;
480 region_age = g_malloc0 (region_age_size);
484 handle_gc_param (const char *opt)
486 if (g_str_has_prefix (opt, "alloc-ratio=")) {
487 const char *arg = strchr (opt, '=') + 1;
488 int percentage = atoi (arg);
489 if (percentage < 1 || percentage > 100) {
490 fprintf (stderr, "alloc-ratio must be an integer in the range 1-100.\n");
493 alloc_ratio = (float)percentage / 100.0f;
497 if (g_str_has_prefix (opt, "promotion-age=")) {
498 const char *arg = strchr (opt, '=') + 1;
499 promote_age = atoi (arg);
500 if (promote_age < 1 || promote_age >= MAX_AGE) {
501 fprintf (stderr, "promotion-age must be an integer in the range 1-%d.\n", MAX_AGE - 1);
510 print_gc_param_usage (void)
514 " alloc-ratio=P (where P is a percentage, an integer in 1-100)\n"
515 " promotion-age=P (where P is a number, an integer in 1-%d)\n",
520 /******************************************Copy/Scan functins ************************************************/
522 #define SGEN_SPLIT_NURSERY
524 #define SERIAL_COPY_OBJECT split_nursery_serial_copy_object
525 #define PARALLEL_COPY_OBJECT split_nursery_parallel_copy_object
526 #define SERIAL_COPY_OBJECT_FROM_OBJ split_nursery_serial_copy_object_from_obj
528 #include "sgen-minor-copy-object.h"
529 #include "sgen-minor-scan-object.h"
532 sgen_split_nursery_init (SgenMinorCollector *collector)
534 collector->is_split = TRUE;
536 collector->alloc_for_promotion = minor_alloc_for_promotion;
537 collector->par_alloc_for_promotion = minor_par_alloc_for_promotion;
539 collector->prepare_to_space = prepare_to_space;
540 collector->clear_fragments = clear_fragments;
541 collector->build_fragments_get_exclude_head = build_fragments_get_exclude_head;
542 collector->build_fragments_release_exclude_head = build_fragments_release_exclude_head;
543 collector->build_fragments_finish = build_fragments_finish;
544 collector->init_nursery = init_nursery;
545 collector->handle_gc_param = handle_gc_param;
546 collector->print_gc_param_usage = print_gc_param_usage;
548 FILL_MINOR_COLLECTOR_COPY_OBJECT (collector);
549 FILL_MINOR_COLLECTOR_SCAN_OBJECT (collector);
550 LOCK_INIT (par_alloc_buffer_refill_mutex);