1 #define JEMALLOC_CHUNK_DSS_C_
2 #include "jemalloc/internal/jemalloc_internal.h"
3 /******************************************************************************/
6 const char *dss_prec_names[] = {
14 * Current dss precedence default, used when creating new arenas. NB: This is
15 * stored as unsigned rather than dss_prec_t because in principle there's no
16 * guarantee that sizeof(dss_prec_t) is the same as sizeof(unsigned), and we use
17 * atomic operations to synchronize the setting.
19 static unsigned dss_prec_default = (unsigned)DSS_PREC_DEFAULT;
21 /* Base address of the DSS. */
22 static void *dss_base;
23 /* Atomic boolean indicating whether the DSS is exhausted. */
24 static unsigned dss_exhausted;
25 /* Atomic current upper limit on DSS addresses. */
28 /******************************************************************************/
31 chunk_dss_sbrk(intptr_t increment)
35 return (sbrk(increment));
43 chunk_dss_prec_get(void)
48 return (dss_prec_disabled);
49 ret = (dss_prec_t)atomic_read_u(&dss_prec_default);
54 chunk_dss_prec_set(dss_prec_t dss_prec)
58 return (dss_prec != dss_prec_disabled);
59 atomic_write_u(&dss_prec_default, (unsigned)dss_prec);
64 chunk_dss_max_update(void *new_addr)
70 * Get the current end of the DSS as max_cur and assure that dss_max is
75 void *max_prev = atomic_read_p(&dss_max);
77 max_cur = chunk_dss_sbrk(0);
78 if ((uintptr_t)max_prev > (uintptr_t)max_cur) {
80 * Another thread optimistically updated dss_max. Wait
83 spin_adaptive(&spinner);
86 if (!atomic_cas_p(&dss_max, max_prev, max_cur))
89 /* Fixed new_addr can only be supported if it is at the edge of DSS. */
90 if (new_addr != NULL && max_cur != new_addr)
97 chunk_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
98 size_t alignment, bool *zero, bool *commit)
101 assert(size > 0 && (size & chunksize_mask) == 0);
102 assert(alignment > 0 && (alignment & chunksize_mask) == 0);
105 * sbrk() uses a signed increment argument, so take care not to
106 * interpret a huge allocation request as a negative increment.
108 if ((intptr_t)size < 0)
111 if (!atomic_read_u(&dss_exhausted)) {
113 * The loop is necessary to recover from races with other
114 * threads that are using the DSS for something other than
118 void *ret, *cpad, *max_cur, *dss_next, *dss_prev;
119 size_t gap_size, cpad_size;
122 max_cur = chunk_dss_max_update(new_addr);
127 * Calculate how much padding is necessary to
128 * chunk-align the end of the DSS.
130 gap_size = (chunksize - CHUNK_ADDR2OFFSET(dss_max)) &
133 * Compute how much chunk-aligned pad space (if any) is
134 * necessary to satisfy alignment. This space can be
135 * recycled for later use.
137 cpad = (void *)((uintptr_t)dss_max + gap_size);
138 ret = (void *)ALIGNMENT_CEILING((uintptr_t)dss_max,
140 cpad_size = (uintptr_t)ret - (uintptr_t)cpad;
141 dss_next = (void *)((uintptr_t)ret + size);
142 if ((uintptr_t)ret < (uintptr_t)dss_max ||
143 (uintptr_t)dss_next < (uintptr_t)dss_max)
144 goto label_oom; /* Wrap-around. */
145 incr = gap_size + cpad_size + size;
148 * Optimistically update dss_max, and roll back below if
149 * sbrk() fails. No other thread will try to extend the
150 * DSS while dss_max is greater than the current DSS
151 * max reported by sbrk(0).
153 if (atomic_cas_p(&dss_max, max_cur, dss_next))
156 /* Try to allocate. */
157 dss_prev = chunk_dss_sbrk(incr);
158 if (dss_prev == max_cur) {
160 if (cpad_size != 0) {
161 chunk_hooks_t chunk_hooks =
162 CHUNK_HOOKS_INITIALIZER;
163 chunk_dalloc_wrapper(tsdn, arena,
164 &chunk_hooks, cpad, cpad_size,
165 arena_extent_sn_next(arena), false,
169 JEMALLOC_VALGRIND_MAKE_MEM_UNDEFINED(
171 memset(ret, 0, size);
174 *commit = pages_decommit(ret, size);
179 * Failure, whether due to OOM or a race with a raw
180 * sbrk() call from outside the allocator. Try to roll
181 * back optimistic dss_max update; if rollback fails,
182 * it's due to another caller of this function having
183 * succeeded since this invocation started, in which
184 * case rollback is not necessary.
186 atomic_cas_p(&dss_max, dss_next, max_cur);
187 if (dss_prev == (void *)-1) {
189 atomic_write_u(&dss_exhausted, (unsigned)true);
199 chunk_in_dss_helper(void *chunk, void *max)
202 return ((uintptr_t)chunk >= (uintptr_t)dss_base && (uintptr_t)chunk <
207 chunk_in_dss(void *chunk)
212 return (chunk_in_dss_helper(chunk, atomic_read_p(&dss_max)));
216 chunk_dss_mergeable(void *chunk_a, void *chunk_b)
222 max = atomic_read_p(&dss_max);
223 return (chunk_in_dss_helper(chunk_a, max) ==
224 chunk_in_dss_helper(chunk_b, max));
233 dss_base = chunk_dss_sbrk(0);
234 dss_exhausted = (unsigned)(dss_base == (void *)-1);
238 /******************************************************************************/