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 size_t region_age_size;
143 static AgeAllocationBuffer age_alloc_buffers [MAX_AGE];
145 /* The collector allocs from here. */
146 static SgenFragmentAllocator collector_allocator;
149 get_object_age (char *object)
151 size_t idx = (object - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
152 return region_age [idx];
156 set_object_age (char *object, int age)
158 size_t idx = (object - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
159 region_age [idx] = age;
163 set_age_in_range (char *start, char *end, int age)
166 size_t region_idx, length;
167 region_idx = (start - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
168 region_start = ®ion_age [region_idx];
169 length = (end - start) >> SGEN_TO_SPACE_GRANULE_BITS;
170 memset (region_start, age, length);
174 mark_bit (char *space_bitmap, char *pos)
176 size_t idx = (pos - sgen_nursery_start) >> SGEN_TO_SPACE_GRANULE_BITS;
177 size_t byte = idx / 8;
180 g_assert (byte < sgen_space_bitmap_size);
181 space_bitmap [byte] |= 1 << bit;
185 mark_bits_in_range (char *space_bitmap, char *start, char *end)
187 start = align_down (start, SGEN_TO_SPACE_GRANULE_BITS);
188 end = align_up (end, SGEN_TO_SPACE_GRANULE_BITS);
190 for (;start < end; start += SGEN_TO_SPACE_GRANULE_IN_BYTES)
191 mark_bit (space_bitmap, start);
195 * This splits the fragments at the point of the promotion barrier.
196 * Two allocator are actually involved here: The mutator allocator and
197 * the collector allocator. This function is called with the
198 * collector, but it's a copy of the mutator allocator and contains
199 * all the fragments in the nursery. The fragments below the
200 * promotion barrier are left with the mutator allocator and the ones
201 * above are put into the collector allocator.
204 fragment_list_split (SgenFragmentAllocator *allocator)
206 SgenFragment *prev = NULL, *list = allocator->region_head;
209 if (list->fragment_end > promotion_barrier) {
210 if (list->fragment_start < promotion_barrier) {
211 SgenFragment *res = sgen_fragment_allocator_alloc ();
213 res->fragment_start = promotion_barrier;
214 res->fragment_next = promotion_barrier;
215 res->fragment_end = list->fragment_end;
216 res->next = list->next;
217 res->next_in_order = list->next_in_order;
218 g_assert (res->fragment_end > res->fragment_start);
220 list->fragment_end = promotion_barrier;
221 list->next = list->next_in_order = NULL;
222 set_age_in_range (list->fragment_start, list->fragment_end, 0);
224 allocator->region_head = allocator->alloc_head = res;
228 prev->next = prev->next_in_order = NULL;
229 allocator->region_head = allocator->alloc_head = list;
233 set_age_in_range (list->fragment_start, list->fragment_end, 0);
237 allocator->region_head = allocator->alloc_head = NULL;
240 /******************************************Minor Collector API ************************************************/
242 #define AGE_ALLOC_BUFFER_MIN_SIZE SGEN_TO_SPACE_GRANULE_IN_BYTES
243 #define AGE_ALLOC_BUFFER_DESIRED_SIZE (SGEN_TO_SPACE_GRANULE_IN_BYTES * 8)
246 alloc_for_promotion_slow_path (int age, size_t objsize)
249 size_t allocated_size;
250 size_t aligned_objsize = (size_t)align_up (objsize, SGEN_TO_SPACE_GRANULE_BITS);
252 p = sgen_fragment_allocator_serial_range_alloc (
253 &collector_allocator,
254 MAX (aligned_objsize, AGE_ALLOC_BUFFER_DESIRED_SIZE),
255 MAX (aligned_objsize, AGE_ALLOC_BUFFER_MIN_SIZE),
258 set_age_in_range (p, p + allocated_size, age);
259 sgen_clear_range (age_alloc_buffers [age].next, age_alloc_buffers [age].end);
260 age_alloc_buffers [age].next = p + objsize;
261 age_alloc_buffers [age].end = p + allocated_size;
267 alloc_for_promotion (MonoVTable *vtable, char *obj, size_t objsize, gboolean has_references)
272 age = get_object_age (obj);
273 if (age >= promote_age)
274 return major_collector.alloc_object (vtable, objsize, has_references);
279 p = age_alloc_buffers [age].next;
280 if (G_LIKELY (p + objsize <= age_alloc_buffers [age].end)) {
281 age_alloc_buffers [age].next += objsize;
283 p = alloc_for_promotion_slow_path (age, objsize);
285 return major_collector.alloc_object (vtable, objsize, has_references);
288 *(MonoVTable**)p = vtable;
294 minor_alloc_for_promotion (MonoVTable *vtable, char *obj, size_t objsize, gboolean has_references)
297 We only need to check for a non-nursery object if we're doing a major collection.
299 if (!sgen_ptr_in_nursery (obj))
300 return major_collector.alloc_object (vtable, objsize, has_references);
302 return alloc_for_promotion (vtable, obj, objsize, has_references);
306 build_fragments_get_exclude_head (void)
309 for (i = 0; i < MAX_AGE; ++i) {
310 /*If we OOM'd on the last collection ->end might be null while ->next not.*/
311 if (age_alloc_buffers [i].end)
312 sgen_clear_range (age_alloc_buffers [i].next, age_alloc_buffers [i].end);
315 return collector_allocator.region_head;
319 build_fragments_release_exclude_head (void)
321 sgen_fragment_allocator_release (&collector_allocator);
325 build_fragments_finish (SgenFragmentAllocator *allocator)
327 /* We split the fragment list based on the promotion barrier. */
328 collector_allocator = *allocator;
329 fragment_list_split (&collector_allocator);
333 prepare_to_space (char *to_space_bitmap, size_t space_bitmap_size)
335 SgenFragment **previous, *frag;
337 memset (to_space_bitmap, 0, space_bitmap_size);
338 memset (age_alloc_buffers, 0, sizeof (age_alloc_buffers));
340 previous = &collector_allocator.alloc_head;
342 for (frag = *previous; frag; frag = *previous) {
343 char *start = align_up (frag->fragment_next, SGEN_TO_SPACE_GRANULE_BITS);
344 char *end = align_down (frag->fragment_end, SGEN_TO_SPACE_GRANULE_BITS);
346 /* Fragment is too small to be usable. */
347 if ((end - start) < SGEN_MAX_NURSERY_WASTE) {
348 sgen_clear_range (frag->fragment_next, frag->fragment_end);
349 frag->fragment_next = frag->fragment_end = frag->fragment_start;
350 *previous = frag->next;
355 We need to insert 3 phony objects so the fragments build step can correctly
359 /* Clean the fragment range. */
360 sgen_clear_range (start, end);
361 /* We need a phony object in between the original fragment start and the effective one. */
362 if (start != frag->fragment_next)
363 sgen_clear_range (frag->fragment_next, start);
364 /* We need an phony object in between the new fragment end and the original fragment end. */
365 if (end != frag->fragment_end)
366 sgen_clear_range (end, frag->fragment_end);
368 frag->fragment_start = frag->fragment_next = start;
369 frag->fragment_end = end;
370 mark_bits_in_range (to_space_bitmap, start, end);
371 previous = &frag->next;
376 clear_fragments (void)
378 sgen_clear_allocator_fragments (&collector_allocator);
382 init_nursery (SgenFragmentAllocator *allocator, char *start, char *end)
384 int alloc_quote = (int)((end - start) * alloc_ratio);
385 promotion_barrier = align_down (start + alloc_quote, 3);
386 sgen_fragment_allocator_add (allocator, start, promotion_barrier);
387 sgen_fragment_allocator_add (&collector_allocator, promotion_barrier, end);
389 region_age_size = (end - start) >> SGEN_TO_SPACE_GRANULE_BITS;
390 region_age = g_malloc0 (region_age_size);
394 handle_gc_param (const char *opt)
396 if (g_str_has_prefix (opt, "alloc-ratio=")) {
397 const char *arg = strchr (opt, '=') + 1;
398 int percentage = atoi (arg);
399 if (percentage < 1 || percentage > 100) {
400 fprintf (stderr, "alloc-ratio must be an integer in the range 1-100.\n");
403 alloc_ratio = (float)percentage / 100.0f;
407 if (g_str_has_prefix (opt, "promotion-age=")) {
408 const char *arg = strchr (opt, '=') + 1;
409 promote_age = atoi (arg);
410 if (promote_age < 1 || promote_age >= MAX_AGE) {
411 fprintf (stderr, "promotion-age must be an integer in the range 1-%d.\n", MAX_AGE - 1);
420 print_gc_param_usage (void)
424 " alloc-ratio=P (where P is a percentage, an integer in 1-100)\n"
425 " promotion-age=P (where P is a number, an integer in 1-%d)\n",
430 /******************************************Copy/Scan functins ************************************************/
432 #define SGEN_SPLIT_NURSERY
434 #define SERIAL_COPY_OBJECT split_nursery_serial_copy_object
435 #define SERIAL_COPY_OBJECT_FROM_OBJ split_nursery_serial_copy_object_from_obj
437 #include "sgen-minor-copy-object.h"
438 #include "sgen-minor-scan-object.h"
441 sgen_split_nursery_init (SgenMinorCollector *collector)
443 collector->is_split = TRUE;
445 collector->alloc_for_promotion = minor_alloc_for_promotion;
447 collector->prepare_to_space = prepare_to_space;
448 collector->clear_fragments = clear_fragments;
449 collector->build_fragments_get_exclude_head = build_fragments_get_exclude_head;
450 collector->build_fragments_release_exclude_head = build_fragments_release_exclude_head;
451 collector->build_fragments_finish = build_fragments_finish;
452 collector->init_nursery = init_nursery;
453 collector->handle_gc_param = handle_gc_param;
454 collector->print_gc_param_usage = print_gc_param_usage;
456 FILL_MINOR_COLLECTOR_COPY_OBJECT (collector);
457 FILL_MINOR_COLLECTOR_SCAN_OBJECT (collector);