1#define JEMALLOC_EXTENT_DSS_C_
2#include "jemalloc/internal/jemalloc_preamble.h"
3#include "jemalloc/internal/jemalloc_internal_includes.h"
4
5#include "jemalloc/internal/assert.h"
6#include "jemalloc/internal/extent_dss.h"
7#include "jemalloc/internal/spin.h"
8
9/******************************************************************************/
10/* Data. */
11
12const char *opt_dss = DSS_DEFAULT;
13
14const char *dss_prec_names[] = {
15 "disabled",
16 "primary",
17 "secondary",
18 "N/A"
19};
20
21/*
22 * Current dss precedence default, used when creating new arenas. NB: This is
23 * stored as unsigned rather than dss_prec_t because in principle there's no
24 * guarantee that sizeof(dss_prec_t) is the same as sizeof(unsigned), and we use
25 * atomic operations to synchronize the setting.
26 */
27static atomic_u_t dss_prec_default = ATOMIC_INIT(
28 (unsigned)DSS_PREC_DEFAULT);
29
30/* Base address of the DSS. */
31static void *dss_base;
32/* Atomic boolean indicating whether a thread is currently extending DSS. */
33static atomic_b_t dss_extending;
34/* Atomic boolean indicating whether the DSS is exhausted. */
35static atomic_b_t dss_exhausted;
36/* Atomic current upper limit on DSS addresses. */
37static atomic_p_t dss_max;
38
39/******************************************************************************/
40
41static void *
42extent_dss_sbrk(intptr_t increment) {
43#ifdef JEMALLOC_DSS
44 return sbrk(increment);
45#else
46 not_implemented();
47 return NULL;
48#endif
49}
50
51dss_prec_t
52extent_dss_prec_get(void) {
53 dss_prec_t ret;
54
55 if (!have_dss) {
56 return dss_prec_disabled;
57 }
58 ret = (dss_prec_t)atomic_load_u(&dss_prec_default, ATOMIC_ACQUIRE);
59 return ret;
60}
61
62bool
63extent_dss_prec_set(dss_prec_t dss_prec) {
64 if (!have_dss) {
65 return (dss_prec != dss_prec_disabled);
66 }
67 atomic_store_u(&dss_prec_default, (unsigned)dss_prec, ATOMIC_RELEASE);
68 return false;
69}
70
71static void
72extent_dss_extending_start(void) {
73 spin_t spinner = SPIN_INITIALIZER;
74 while (true) {
75 bool expected = false;
76 if (atomic_compare_exchange_weak_b(&dss_extending, &expected,
77 true, ATOMIC_ACQ_REL, ATOMIC_RELAXED)) {
78 break;
79 }
80 spin_adaptive(&spinner);
81 }
82}
83
84static void
85extent_dss_extending_finish(void) {
86 assert(atomic_load_b(&dss_extending, ATOMIC_RELAXED));
87
88 atomic_store_b(&dss_extending, false, ATOMIC_RELEASE);
89}
90
91static void *
92extent_dss_max_update(void *new_addr) {
93 /*
94 * Get the current end of the DSS as max_cur and assure that dss_max is
95 * up to date.
96 */
97 void *max_cur = extent_dss_sbrk(0);
98 if (max_cur == (void *)-1) {
99 return NULL;
100 }
101 atomic_store_p(&dss_max, max_cur, ATOMIC_RELEASE);
102 /* Fixed new_addr can only be supported if it is at the edge of DSS. */
103 if (new_addr != NULL && max_cur != new_addr) {
104 return NULL;
105 }
106 return max_cur;
107}
108
109void *
110extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
111 size_t alignment, bool *zero, bool *commit) {
112 extent_t *gap;
113
114 cassert(have_dss);
115 assert(size > 0);
116 assert(alignment > 0);
117
118 /*
119 * sbrk() uses a signed increment argument, so take care not to
120 * interpret a large allocation request as a negative increment.
121 */
122 if ((intptr_t)size < 0) {
123 return NULL;
124 }
125
126 gap = extent_alloc(tsdn, arena);
127 if (gap == NULL) {
128 return NULL;
129 }
130
131 extent_dss_extending_start();
132 if (!atomic_load_b(&dss_exhausted, ATOMIC_ACQUIRE)) {
133 /*
134 * The loop is necessary to recover from races with other
135 * threads that are using the DSS for something other than
136 * malloc.
137 */
138 while (true) {
139 void *max_cur = extent_dss_max_update(new_addr);
140 if (max_cur == NULL) {
141 goto label_oom;
142 }
143
144 /*
145 * Compute how much page-aligned gap space (if any) is
146 * necessary to satisfy alignment. This space can be
147 * recycled for later use.
148 */
149 void *gap_addr_page = (void *)(PAGE_CEILING(
150 (uintptr_t)max_cur));
151 void *ret = (void *)ALIGNMENT_CEILING(
152 (uintptr_t)gap_addr_page, alignment);
153 size_t gap_size_page = (uintptr_t)ret -
154 (uintptr_t)gap_addr_page;
155 if (gap_size_page != 0) {
156 extent_init(gap, arena, gap_addr_page,
157 gap_size_page, false, SC_NSIZES,
158 arena_extent_sn_next(arena),
159 extent_state_active, false, true, true);
160 }
161 /*
162 * Compute the address just past the end of the desired
163 * allocation space.
164 */
165 void *dss_next = (void *)((uintptr_t)ret + size);
166 if ((uintptr_t)ret < (uintptr_t)max_cur ||
167 (uintptr_t)dss_next < (uintptr_t)max_cur) {
168 goto label_oom; /* Wrap-around. */
169 }
170 /* Compute the increment, including subpage bytes. */
171 void *gap_addr_subpage = max_cur;
172 size_t gap_size_subpage = (uintptr_t)ret -
173 (uintptr_t)gap_addr_subpage;
174 intptr_t incr = gap_size_subpage + size;
175
176 assert((uintptr_t)max_cur + incr == (uintptr_t)ret +
177 size);
178
179 /* Try to allocate. */
180 void *dss_prev = extent_dss_sbrk(incr);
181 if (dss_prev == max_cur) {
182 /* Success. */
183 atomic_store_p(&dss_max, dss_next,
184 ATOMIC_RELEASE);
185 extent_dss_extending_finish();
186
187 if (gap_size_page != 0) {
188 extent_dalloc_gap(tsdn, arena, gap);
189 } else {
190 extent_dalloc(tsdn, arena, gap);
191 }
192 if (!*commit) {
193 *commit = pages_decommit(ret, size);
194 }
195 if (*zero && *commit) {
196 extent_hooks_t *extent_hooks =
197 EXTENT_HOOKS_INITIALIZER;
198 extent_t extent;
199
200 extent_init(&extent, arena, ret, size,
201 size, false, SC_NSIZES,
202 extent_state_active, false, true,
203 true);
204 if (extent_purge_forced_wrapper(tsdn,
205 arena, &extent_hooks, &extent, 0,
206 size)) {
207 memset(ret, 0, size);
208 }
209 }
210 return ret;
211 }
212 /*
213 * Failure, whether due to OOM or a race with a raw
214 * sbrk() call from outside the allocator.
215 */
216 if (dss_prev == (void *)-1) {
217 /* OOM. */
218 atomic_store_b(&dss_exhausted, true,
219 ATOMIC_RELEASE);
220 goto label_oom;
221 }
222 }
223 }
224label_oom:
225 extent_dss_extending_finish();
226 extent_dalloc(tsdn, arena, gap);
227 return NULL;
228}
229
230static bool
231extent_in_dss_helper(void *addr, void *max) {
232 return ((uintptr_t)addr >= (uintptr_t)dss_base && (uintptr_t)addr <
233 (uintptr_t)max);
234}
235
236bool
237extent_in_dss(void *addr) {
238 cassert(have_dss);
239
240 return extent_in_dss_helper(addr, atomic_load_p(&dss_max,
241 ATOMIC_ACQUIRE));
242}
243
244bool
245extent_dss_mergeable(void *addr_a, void *addr_b) {
246 void *max;
247
248 cassert(have_dss);
249
250 if ((uintptr_t)addr_a < (uintptr_t)dss_base && (uintptr_t)addr_b <
251 (uintptr_t)dss_base) {
252 return true;
253 }
254
255 max = atomic_load_p(&dss_max, ATOMIC_ACQUIRE);
256 return (extent_in_dss_helper(addr_a, max) ==
257 extent_in_dss_helper(addr_b, max));
258}
259
260void
261extent_dss_boot(void) {
262 cassert(have_dss);
263
264 dss_base = extent_dss_sbrk(0);
265 atomic_store_b(&dss_extending, false, ATOMIC_RELAXED);
266 atomic_store_b(&dss_exhausted, dss_base == (void *)-1, ATOMIC_RELAXED);
267 atomic_store_p(&dss_max, dss_base, ATOMIC_RELAXED);
268}
269
270/******************************************************************************/
271