aboutsummaryrefslogtreecommitdiff
path: root/mm/vmpressure.c
blob: d4042e75f7c7e7c7d498c4fcc33c90f1d1de2bff (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
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
/*
 * Linux VM pressure
 *
 * Copyright 2012 Linaro Ltd.
 *		  Anton Vorontsov <anton.vorontsov@linaro.org>
 *
 * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
 * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation.
 */

#include <linux/cgroup.h>
#include <linux/fs.h>
#include <linux/log2.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/vmstat.h>
#include <linux/eventfd.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/printk.h>
#include <linux/vmpressure.h>

/*
 * The window size (vmpressure_win) is the number of scanned pages before
 * we try to analyze scanned/reclaimed ratio. So the window is used as a
 * rate-limit tunable for the "low" level notification, and also for
 * averaging the ratio for medium/critical levels. Using small window
 * sizes can cause lot of false positives, but too big window size will
 * delay the notifications.
 *
 * As the vmscan reclaimer logic works with chunks which are multiple of
 * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
 *
 * TODO: Make the window size depend on machine size, as we do for vmstat
 * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
 */
static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;

/*
 * These thresholds are used when we account memory pressure through
 * scanned/reclaimed ratio. The current values were chosen empirically. In
 * essence, they are percents: the higher the value, the more number
 * unsuccessful reclaims there were.
 */
static const unsigned int vmpressure_level_med = 60;
static const unsigned int vmpressure_level_critical = 95;

/*
 * When there are too little pages left to scan, vmpressure() may miss the
 * critical pressure as number of pages will be less than "window size".
 * However, in that case the vmscan priority will raise fast as the
 * reclaimer will try to scan LRUs more deeply.
 *
 * The vmscan logic considers these special priorities:
 *
 * prio == DEF_PRIORITY (12): reclaimer starts with that value
 * prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed
 * prio == 0                : close to OOM, kernel scans every page in an lru
 *
 * Any value in this range is acceptable for this tunable (i.e. from 12 to
 * 0). Current value for the vmpressure_level_critical_prio is chosen
 * empirically, but the number, in essence, means that we consider
 * critical level when scanning depth is ~10% of the lru size (vmscan
 * scans 'lru_size >> prio' pages, so it is actually 12.5%, or one
 * eights).
 */
static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);

static struct vmpressure *work_to_vmpressure(struct work_struct *work)
{
	return container_of(work, struct vmpressure, work);
}

static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
{
	struct cgroup_subsys_state *css = vmpressure_to_css(vmpr);
	struct mem_cgroup *memcg = mem_cgroup_from_css(css);

	memcg = parent_mem_cgroup(memcg);
	if (!memcg)
		return NULL;
	return memcg_to_vmpressure(memcg);
}

enum vmpressure_levels {
	VMPRESSURE_LOW = 0,
	VMPRESSURE_MEDIUM,
	VMPRESSURE_CRITICAL,
	VMPRESSURE_NUM_LEVELS,
};

static const char * const vmpressure_str_levels[] = {
	[VMPRESSURE_LOW] = "low",
	[VMPRESSURE_MEDIUM] = "medium",
	[VMPRESSURE_CRITICAL] = "critical",
};

static enum vmpressure_levels vmpressure_level(unsigned long pressure)
{
	if (pressure >= vmpressure_level_critical)
		return VMPRESSURE_CRITICAL;
	else if (pressure >= vmpressure_level_med)
		return VMPRESSURE_MEDIUM;
	return VMPRESSURE_LOW;
}

static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
						    unsigned long reclaimed)
{
	unsigned long scale = scanned + reclaimed;
	unsigned long pressure;

	/*
	 * We calculate the ratio (in percents) of how many pages were
	 * scanned vs. reclaimed in a given time frame (window). Note that
	 * time is in VM reclaimer's "ticks", i.e. number of pages
	 * scanned. This makes it possible to set desired reaction time
	 * and serves as a ratelimit.
	 */
	pressure = scale - (reclaimed * scale / scanned);
	pressure = pressure * 100 / scale;

	pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
		 scanned, reclaimed);

	return vmpressure_level(pressure);
}

struct vmpressure_event {
	struct eventfd_ctx *efd;
	enum vmpressure_levels level;
	struct list_head node;
};

static bool vmpressure_event(struct vmpressure *vmpr,
			     unsigned long scanned, unsigned long reclaimed)
{
	struct vmpressure_event *ev;
	enum vmpressure_levels level;
	bool signalled = false;

	level = vmpressure_calc_level(scanned, reclaimed);

	mutex_lock(&vmpr->events_lock);

	list_for_each_entry(ev, &vmpr->events, node) {
		if (level >= ev->level) {
			eventfd_signal(ev->efd, 1);
			signalled = true;
		}
	}

	mutex_unlock(&vmpr->events_lock);

	return signalled;
}

static void vmpressure_work_fn(struct work_struct *work)
{
	struct vmpressure *vmpr = work_to_vmpressure(work);
	unsigned long scanned;
	unsigned long reclaimed;

	/*
	 * Several contexts might be calling vmpressure(), so it is
	 * possible that the work was rescheduled again before the old
	 * work context cleared the counters. In that case we will run
	 * just after the old work returns, but then scanned might be zero
	 * here. No need for any locks here since we don't care if
	 * vmpr->reclaimed is in sync.
	 */
	if (!vmpr->scanned)
		return;

	spin_lock(&vmpr->sr_lock);
	scanned = vmpr->scanned;
	reclaimed = vmpr->reclaimed;
	vmpr->scanned = 0;
	vmpr->reclaimed = 0;
	spin_unlock(&vmpr->sr_lock);

	do {
		if (vmpressure_event(vmpr, scanned, reclaimed))
			break;
		/*
		 * If not handled, propagate the event upward into the
		 * hierarchy.
		 */
	} while ((vmpr = vmpressure_parent(vmpr)));
}

/**
 * vmpressure() - Account memory pressure through scanned/reclaimed ratio
 * @gfp:	reclaimer's gfp mask
 * @memcg:	cgroup memory controller handle
 * @scanned:	number of pages scanned
 * @reclaimed:	number of pages reclaimed
 *
 * This function should be called from the vmscan reclaim path to account
 * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
 * pressure index is then further refined and averaged over time.
 *
 * This function does not return any value.
 */
void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
		unsigned long scanned, unsigned long reclaimed)
{
	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);

	/*
	 * Here we only want to account pressure that userland is able to
	 * help us with. For example, suppose that DMA zone is under
	 * pressure; if we notify userland about that kind of pressure,
	 * then it will be mostly a waste as it will trigger unnecessary
	 * freeing of memory by userland (since userland is more likely to
	 * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
	 * is why we include only movable, highmem and FS/IO pages.
	 * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
	 * we account it too.
	 */
	if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
		return;

	/*
	 * If we got here with no pages scanned, then that is an indicator
	 * that reclaimer was unable to find any shrinkable LRUs at the
	 * current scanning depth. But it does not mean that we should
	 * report the critical pressure, yet. If the scanning priority
	 * (scanning depth) goes too high (deep), we will be notified
	 * through vmpressure_prio(). But so far, keep calm.
	 */
	if (!scanned)
		return;

	spin_lock(&vmpr->sr_lock);
	vmpr->scanned += scanned;
	vmpr->reclaimed += reclaimed;
	scanned = vmpr->scanned;
	spin_unlock(&vmpr->sr_lock);

	if (scanned < vmpressure_win)
		return;
	schedule_work(&vmpr->work);
}

/**
 * vmpressure_prio() - Account memory pressure through reclaimer priority level
 * @gfp:	reclaimer's gfp mask
 * @memcg:	cgroup memory controller handle
 * @prio:	reclaimer's priority
 *
 * This function should be called from the reclaim path every time when
 * the vmscan's reclaiming priority (scanning depth) changes.
 *
 * This function does not return any value.
 */
void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
{
	/*
	 * We only use prio for accounting critical level. For more info
	 * see comment for vmpressure_level_critical_prio variable above.
	 */
	if (prio > vmpressure_level_critical_prio)
		return;

	/*
	 * OK, the prio is below the threshold, updating vmpressure
	 * information before shrinker dives into long shrinking of long
	 * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
	 * to the vmpressure() basically means that we signal 'critical'
	 * level.
	 */
	vmpressure(gfp, memcg, vmpressure_win, 0);
}

/**
 * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
 * @memcg:	memcg that is interested in vmpressure notifications
 * @eventfd:	eventfd context to link notifications with
 * @args:	event arguments (used to set up a pressure level threshold)
 *
 * This function associates eventfd context with the vmpressure
 * infrastructure, so that the notifications will be delivered to the
 * @eventfd. The @args parameter is a string that denotes pressure level
 * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
 * "critical").
 *
 * To be used as memcg event method.
 */
int vmpressure_register_event(struct mem_cgroup *memcg,
			      struct eventfd_ctx *eventfd, const char *args)
{
	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
	struct vmpressure_event *ev;
	int level;

	for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
		if (!strcmp(vmpressure_str_levels[level], args))
			break;
	}

	if (level >= VMPRESSURE_NUM_LEVELS)
		return -EINVAL;

	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
	if (!ev)
		return -ENOMEM;

	ev->efd = eventfd;
	ev->level = level;

	mutex_lock(&vmpr->events_lock);
	list_add(&ev->node, &vmpr->events);
	mutex_unlock(&vmpr->events_lock);

	return 0;
}

/**
 * vmpressure_unregister_event() - Unbind eventfd from vmpressure
 * @memcg:	memcg handle
 * @eventfd:	eventfd context that was used to link vmpressure with the @cg
 *
 * This function does internal manipulations to detach the @eventfd from
 * the vmpressure notifications, and then frees internal resources
 * associated with the @eventfd (but the @eventfd itself is not freed).
 *
 * To be used as memcg event method.
 */
void vmpressure_unregister_event(struct mem_cgroup *memcg,
				 struct eventfd_ctx *eventfd)
{
	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
	struct vmpressure_event *ev;

	mutex_lock(&vmpr->events_lock);
	list_for_each_entry(ev, &vmpr->events, node) {
		if (ev->efd != eventfd)
			continue;
		list_del(&ev->node);
		kfree(ev);
		break;
	}
	mutex_unlock(&vmpr->events_lock);
}

/**
 * vmpressure_init() - Initialize vmpressure control structure
 * @vmpr:	Structure to be initialized
 *
 * This function should be called on every allocated vmpressure structure
 * before any usage.
 */
void vmpressure_init(struct vmpressure *vmpr)
{
	spin_lock_init(&vmpr->sr_lock);
	mutex_init(&vmpr->events_lock);
	INIT_LIST_HEAD(&vmpr->events);
	INIT_WORK(&vmpr->work, vmpressure_work_fn);
}

/**
 * vmpressure_cleanup() - shuts down vmpressure control structure
 * @vmpr:	Structure to be cleaned up
 *
 * This function should be called before the structure in which it is
 * embedded is cleaned up.
 */
void vmpressure_cleanup(struct vmpressure *vmpr)
{
	/*
	 * Make sure there is no pending work before eventfd infrastructure
	 * goes away.
	 */
	flush_work(&vmpr->work);
}