summaryrefslogtreecommitdiffstats
path: root/fluent-bit/lib/jemalloc-5.3.0/src/decay.c
blob: d801b2bc08ea993aa6a37c198a518f3013b5cdc5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
#include "jemalloc/internal/jemalloc_preamble.h"
#include "jemalloc/internal/jemalloc_internal_includes.h"

#include "jemalloc/internal/decay.h"

static const uint64_t h_steps[SMOOTHSTEP_NSTEPS] = {
#define STEP(step, h, x, y)			\
		h,
		SMOOTHSTEP
#undef STEP
};

/*
 * Generate a new deadline that is uniformly random within the next epoch after
 * the current one.
 */
void
decay_deadline_init(decay_t *decay) {
	nstime_copy(&decay->deadline, &decay->epoch);
	nstime_add(&decay->deadline, &decay->interval);
	if (decay_ms_read(decay) > 0) {
		nstime_t jitter;

		nstime_init(&jitter, prng_range_u64(&decay->jitter_state,
		    nstime_ns(&decay->interval)));
		nstime_add(&decay->deadline, &jitter);
	}
}

void
decay_reinit(decay_t *decay, nstime_t *cur_time, ssize_t decay_ms) {
	atomic_store_zd(&decay->time_ms, decay_ms, ATOMIC_RELAXED);
	if (decay_ms > 0) {
		nstime_init(&decay->interval, (uint64_t)decay_ms *
		    KQU(1000000));
		nstime_idivide(&decay->interval, SMOOTHSTEP_NSTEPS);
	}

	nstime_copy(&decay->epoch, cur_time);
	decay->jitter_state = (uint64_t)(uintptr_t)decay;
	decay_deadline_init(decay);
	decay->nunpurged = 0;
	memset(decay->backlog, 0, SMOOTHSTEP_NSTEPS * sizeof(size_t));
}

bool
decay_init(decay_t *decay, nstime_t *cur_time, ssize_t decay_ms) {
	if (config_debug) {
		for (size_t i = 0; i < sizeof(decay_t); i++) {
			assert(((char *)decay)[i] == 0);
		}
		decay->ceil_npages = 0;
	}
	if (malloc_mutex_init(&decay->mtx, "decay", WITNESS_RANK_DECAY,
	    malloc_mutex_rank_exclusive)) {
		return true;
	}
	decay->purging = false;
	decay_reinit(decay, cur_time, decay_ms);
	return false;
}

bool
decay_ms_valid(ssize_t decay_ms) {
	if (decay_ms < -1) {
		return false;
	}
	if (decay_ms == -1 || (uint64_t)decay_ms <= NSTIME_SEC_MAX *
	    KQU(1000)) {
		return true;
	}
	return false;
}

static void
decay_maybe_update_time(decay_t *decay, nstime_t *new_time) {
	if (unlikely(!nstime_monotonic() && nstime_compare(&decay->epoch,
	    new_time) > 0)) {
		/*
		 * Time went backwards.  Move the epoch back in time and
		 * generate a new deadline, with the expectation that time
		 * typically flows forward for long enough periods of time that
		 * epochs complete.  Unfortunately, this strategy is susceptible
		 * to clock jitter triggering premature epoch advances, but
		 * clock jitter estimation and compensation isn't feasible here
		 * because calls into this code are event-driven.
		 */
		nstime_copy(&decay->epoch, new_time);
		decay_deadline_init(decay);
	} else {
		/* Verify that time does not go backwards. */
		assert(nstime_compare(&decay->epoch, new_time) <= 0);
	}
}

static size_t
decay_backlog_npages_limit(const decay_t *decay) {
	/*
	 * For each element of decay_backlog, multiply by the corresponding
	 * fixed-point smoothstep decay factor.  Sum the products, then divide
	 * to round down to the nearest whole number of pages.
	 */
	uint64_t sum = 0;
	for (unsigned i = 0; i < SMOOTHSTEP_NSTEPS; i++) {
		sum += decay->backlog[i] * h_steps[i];
	}
	size_t npages_limit_backlog = (size_t)(sum >> SMOOTHSTEP_BFP);

	return npages_limit_backlog;
}

/*
 * Update backlog, assuming that 'nadvance_u64' time intervals have passed.
 * Trailing 'nadvance_u64' records should be erased and 'current_npages' is
 * placed as the newest record.
 */
static void
decay_backlog_update(decay_t *decay, uint64_t nadvance_u64,
    size_t current_npages) {
	if (nadvance_u64 >= SMOOTHSTEP_NSTEPS) {
		memset(decay->backlog, 0, (SMOOTHSTEP_NSTEPS-1) *
		    sizeof(size_t));
	} else {
		size_t nadvance_z = (size_t)nadvance_u64;

		assert((uint64_t)nadvance_z == nadvance_u64);

		memmove(decay->backlog, &decay->backlog[nadvance_z],
		    (SMOOTHSTEP_NSTEPS - nadvance_z) * sizeof(size_t));
		if (nadvance_z > 1) {
			memset(&decay->backlog[SMOOTHSTEP_NSTEPS -
			    nadvance_z], 0, (nadvance_z-1) * sizeof(size_t));
		}
	}

	size_t npages_delta = (current_npages > decay->nunpurged) ?
	    current_npages - decay->nunpurged : 0;
	decay->backlog[SMOOTHSTEP_NSTEPS-1] = npages_delta;

	if (config_debug) {
		if (current_npages > decay->ceil_npages) {
			decay->ceil_npages = current_npages;
		}
		size_t npages_limit = decay_backlog_npages_limit(decay);
		assert(decay->ceil_npages >= npages_limit);
		if (decay->ceil_npages > npages_limit) {
			decay->ceil_npages = npages_limit;
		}
	}
}

static inline bool
decay_deadline_reached(const decay_t *decay, const nstime_t *time) {
	return (nstime_compare(&decay->deadline, time) <= 0);
}

uint64_t
decay_npages_purge_in(decay_t *decay, nstime_t *time, size_t npages_new) {
	uint64_t decay_interval_ns = decay_epoch_duration_ns(decay);
	size_t n_epoch = (size_t)(nstime_ns(time) / decay_interval_ns);

	uint64_t npages_purge;
	if (n_epoch >= SMOOTHSTEP_NSTEPS) {
		npages_purge = npages_new;
	} else {
		uint64_t h_steps_max = h_steps[SMOOTHSTEP_NSTEPS - 1];
		assert(h_steps_max >=
		    h_steps[SMOOTHSTEP_NSTEPS - 1 - n_epoch]);
		npages_purge = npages_new * (h_steps_max -
		    h_steps[SMOOTHSTEP_NSTEPS - 1 - n_epoch]);
		npages_purge >>= SMOOTHSTEP_BFP;
	}
	return npages_purge;
}

bool
decay_maybe_advance_epoch(decay_t *decay, nstime_t *new_time,
    size_t npages_current) {
	/* Handle possible non-monotonicity of time. */
	decay_maybe_update_time(decay, new_time);

	if (!decay_deadline_reached(decay, new_time)) {
		return false;
	}
	nstime_t delta;
	nstime_copy(&delta, new_time);
	nstime_subtract(&delta, &decay->epoch);

	uint64_t nadvance_u64 = nstime_divide(&delta, &decay->interval);
	assert(nadvance_u64 > 0);

	/* Add nadvance_u64 decay intervals to epoch. */
	nstime_copy(&delta, &decay->interval);
	nstime_imultiply(&delta, nadvance_u64);
	nstime_add(&decay->epoch, &delta);

	/* Set a new deadline. */
	decay_deadline_init(decay);

	/* Update the backlog. */
	decay_backlog_update(decay, nadvance_u64, npages_current);

	decay->npages_limit = decay_backlog_npages_limit(decay);
	decay->nunpurged = (decay->npages_limit > npages_current) ?
	    decay->npages_limit : npages_current;

	return true;
}

/*
 * Calculate how many pages should be purged after 'interval'.
 *
 * First, calculate how many pages should remain at the moment, then subtract
 * the number of pages that should remain after 'interval'. The difference is
 * how many pages should be purged until then.
 *
 * The number of pages that should remain at a specific moment is calculated
 * like this: pages(now) = sum(backlog[i] * h_steps[i]). After 'interval'
 * passes, backlog would shift 'interval' positions to the left and sigmoid
 * curve would be applied starting with backlog[interval].
 *
 * The implementation doesn't directly map to the description, but it's
 * essentially the same calculation, optimized to avoid iterating over
 * [interval..SMOOTHSTEP_NSTEPS) twice.
 */
static inline size_t
decay_npurge_after_interval(decay_t *decay, size_t interval) {
	size_t i;
	uint64_t sum = 0;
	for (i = 0; i < interval; i++) {
		sum += decay->backlog[i] * h_steps[i];
	}
	for (; i < SMOOTHSTEP_NSTEPS; i++) {
		sum += decay->backlog[i] *
		    (h_steps[i] - h_steps[i - interval]);
	}

	return (size_t)(sum >> SMOOTHSTEP_BFP);
}

uint64_t decay_ns_until_purge(decay_t *decay, size_t npages_current,
    uint64_t npages_threshold) {
	if (!decay_gradually(decay)) {
		return DECAY_UNBOUNDED_TIME_TO_PURGE;
	}
	uint64_t decay_interval_ns = decay_epoch_duration_ns(decay);
	assert(decay_interval_ns > 0);
	if (npages_current == 0) {
		unsigned i;
		for (i = 0; i < SMOOTHSTEP_NSTEPS; i++) {
			if (decay->backlog[i] > 0) {
				break;
			}
		}
		if (i == SMOOTHSTEP_NSTEPS) {
			/* No dirty pages recorded.  Sleep indefinitely. */
			return DECAY_UNBOUNDED_TIME_TO_PURGE;
		}
	}
	if (npages_current <= npages_threshold) {
		/* Use max interval. */
		return decay_interval_ns * SMOOTHSTEP_NSTEPS;
	}

	/* Minimal 2 intervals to ensure reaching next epoch deadline. */
	size_t lb = 2;
	size_t ub = SMOOTHSTEP_NSTEPS;

	size_t npurge_lb, npurge_ub;
	npurge_lb = decay_npurge_after_interval(decay, lb);
	if (npurge_lb > npages_threshold) {
		return decay_interval_ns * lb;
	}
	npurge_ub = decay_npurge_after_interval(decay, ub);
	if (npurge_ub < npages_threshold) {
		return decay_interval_ns * ub;
	}

	unsigned n_search = 0;
	size_t target, npurge;
	while ((npurge_lb + npages_threshold < npurge_ub) && (lb + 2 < ub)) {
		target = (lb + ub) / 2;
		npurge = decay_npurge_after_interval(decay, target);
		if (npurge > npages_threshold) {
			ub = target;
			npurge_ub = npurge;
		} else {
			lb = target;
			npurge_lb = npurge;
		}
		assert(n_search < lg_floor(SMOOTHSTEP_NSTEPS) + 1);
		++n_search;
	}
	return decay_interval_ns * (ub + lb) / 2;
}