xref: /openbmc/linux/mm/vmpressure.c (revision 4f6cce39)
1 /*
2  * Linux VM pressure
3  *
4  * Copyright 2012 Linaro Ltd.
5  *		  Anton Vorontsov <anton.vorontsov@linaro.org>
6  *
7  * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
8  * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
9  *
10  * This program is free software; you can redistribute it and/or modify it
11  * under the terms of the GNU General Public License version 2 as published
12  * by the Free Software Foundation.
13  */
14 
15 #include <linux/cgroup.h>
16 #include <linux/fs.h>
17 #include <linux/log2.h>
18 #include <linux/sched.h>
19 #include <linux/mm.h>
20 #include <linux/vmstat.h>
21 #include <linux/eventfd.h>
22 #include <linux/slab.h>
23 #include <linux/swap.h>
24 #include <linux/printk.h>
25 #include <linux/vmpressure.h>
26 
27 /*
28  * The window size (vmpressure_win) is the number of scanned pages before
29  * we try to analyze scanned/reclaimed ratio. So the window is used as a
30  * rate-limit tunable for the "low" level notification, and also for
31  * averaging the ratio for medium/critical levels. Using small window
32  * sizes can cause lot of false positives, but too big window size will
33  * delay the notifications.
34  *
35  * As the vmscan reclaimer logic works with chunks which are multiple of
36  * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
37  *
38  * TODO: Make the window size depend on machine size, as we do for vmstat
39  * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
40  */
41 static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
42 
43 /*
44  * These thresholds are used when we account memory pressure through
45  * scanned/reclaimed ratio. The current values were chosen empirically. In
46  * essence, they are percents: the higher the value, the more number
47  * unsuccessful reclaims there were.
48  */
49 static const unsigned int vmpressure_level_med = 60;
50 static const unsigned int vmpressure_level_critical = 95;
51 
52 /*
53  * When there are too little pages left to scan, vmpressure() may miss the
54  * critical pressure as number of pages will be less than "window size".
55  * However, in that case the vmscan priority will raise fast as the
56  * reclaimer will try to scan LRUs more deeply.
57  *
58  * The vmscan logic considers these special priorities:
59  *
60  * prio == DEF_PRIORITY (12): reclaimer starts with that value
61  * prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed
62  * prio == 0                : close to OOM, kernel scans every page in an lru
63  *
64  * Any value in this range is acceptable for this tunable (i.e. from 12 to
65  * 0). Current value for the vmpressure_level_critical_prio is chosen
66  * empirically, but the number, in essence, means that we consider
67  * critical level when scanning depth is ~10% of the lru size (vmscan
68  * scans 'lru_size >> prio' pages, so it is actually 12.5%, or one
69  * eights).
70  */
71 static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);
72 
73 static struct vmpressure *work_to_vmpressure(struct work_struct *work)
74 {
75 	return container_of(work, struct vmpressure, work);
76 }
77 
78 static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
79 {
80 	struct cgroup_subsys_state *css = vmpressure_to_css(vmpr);
81 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
82 
83 	memcg = parent_mem_cgroup(memcg);
84 	if (!memcg)
85 		return NULL;
86 	return memcg_to_vmpressure(memcg);
87 }
88 
89 enum vmpressure_levels {
90 	VMPRESSURE_LOW = 0,
91 	VMPRESSURE_MEDIUM,
92 	VMPRESSURE_CRITICAL,
93 	VMPRESSURE_NUM_LEVELS,
94 };
95 
96 static const char * const vmpressure_str_levels[] = {
97 	[VMPRESSURE_LOW] = "low",
98 	[VMPRESSURE_MEDIUM] = "medium",
99 	[VMPRESSURE_CRITICAL] = "critical",
100 };
101 
102 static enum vmpressure_levels vmpressure_level(unsigned long pressure)
103 {
104 	if (pressure >= vmpressure_level_critical)
105 		return VMPRESSURE_CRITICAL;
106 	else if (pressure >= vmpressure_level_med)
107 		return VMPRESSURE_MEDIUM;
108 	return VMPRESSURE_LOW;
109 }
110 
111 static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
112 						    unsigned long reclaimed)
113 {
114 	unsigned long scale = scanned + reclaimed;
115 	unsigned long pressure = 0;
116 
117 	/*
118 	 * reclaimed can be greater than scanned in cases
119 	 * like THP, where the scanned is 1 and reclaimed
120 	 * could be 512
121 	 */
122 	if (reclaimed >= scanned)
123 		goto out;
124 	/*
125 	 * We calculate the ratio (in percents) of how many pages were
126 	 * scanned vs. reclaimed in a given time frame (window). Note that
127 	 * time is in VM reclaimer's "ticks", i.e. number of pages
128 	 * scanned. This makes it possible to set desired reaction time
129 	 * and serves as a ratelimit.
130 	 */
131 	pressure = scale - (reclaimed * scale / scanned);
132 	pressure = pressure * 100 / scale;
133 
134 out:
135 	pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
136 		 scanned, reclaimed);
137 
138 	return vmpressure_level(pressure);
139 }
140 
141 struct vmpressure_event {
142 	struct eventfd_ctx *efd;
143 	enum vmpressure_levels level;
144 	struct list_head node;
145 };
146 
147 static bool vmpressure_event(struct vmpressure *vmpr,
148 			     enum vmpressure_levels level)
149 {
150 	struct vmpressure_event *ev;
151 	bool signalled = false;
152 
153 	mutex_lock(&vmpr->events_lock);
154 
155 	list_for_each_entry(ev, &vmpr->events, node) {
156 		if (level >= ev->level) {
157 			eventfd_signal(ev->efd, 1);
158 			signalled = true;
159 		}
160 	}
161 
162 	mutex_unlock(&vmpr->events_lock);
163 
164 	return signalled;
165 }
166 
167 static void vmpressure_work_fn(struct work_struct *work)
168 {
169 	struct vmpressure *vmpr = work_to_vmpressure(work);
170 	unsigned long scanned;
171 	unsigned long reclaimed;
172 	enum vmpressure_levels level;
173 
174 	spin_lock(&vmpr->sr_lock);
175 	/*
176 	 * Several contexts might be calling vmpressure(), so it is
177 	 * possible that the work was rescheduled again before the old
178 	 * work context cleared the counters. In that case we will run
179 	 * just after the old work returns, but then scanned might be zero
180 	 * here. No need for any locks here since we don't care if
181 	 * vmpr->reclaimed is in sync.
182 	 */
183 	scanned = vmpr->tree_scanned;
184 	if (!scanned) {
185 		spin_unlock(&vmpr->sr_lock);
186 		return;
187 	}
188 
189 	reclaimed = vmpr->tree_reclaimed;
190 	vmpr->tree_scanned = 0;
191 	vmpr->tree_reclaimed = 0;
192 	spin_unlock(&vmpr->sr_lock);
193 
194 	level = vmpressure_calc_level(scanned, reclaimed);
195 
196 	do {
197 		if (vmpressure_event(vmpr, level))
198 			break;
199 		/*
200 		 * If not handled, propagate the event upward into the
201 		 * hierarchy.
202 		 */
203 	} while ((vmpr = vmpressure_parent(vmpr)));
204 }
205 
206 /**
207  * vmpressure() - Account memory pressure through scanned/reclaimed ratio
208  * @gfp:	reclaimer's gfp mask
209  * @memcg:	cgroup memory controller handle
210  * @tree:	legacy subtree mode
211  * @scanned:	number of pages scanned
212  * @reclaimed:	number of pages reclaimed
213  *
214  * This function should be called from the vmscan reclaim path to account
215  * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
216  * pressure index is then further refined and averaged over time.
217  *
218  * If @tree is set, vmpressure is in traditional userspace reporting
219  * mode: @memcg is considered the pressure root and userspace is
220  * notified of the entire subtree's reclaim efficiency.
221  *
222  * If @tree is not set, reclaim efficiency is recorded for @memcg, and
223  * only in-kernel users are notified.
224  *
225  * This function does not return any value.
226  */
227 void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
228 		unsigned long scanned, unsigned long reclaimed)
229 {
230 	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
231 
232 	/*
233 	 * Here we only want to account pressure that userland is able to
234 	 * help us with. For example, suppose that DMA zone is under
235 	 * pressure; if we notify userland about that kind of pressure,
236 	 * then it will be mostly a waste as it will trigger unnecessary
237 	 * freeing of memory by userland (since userland is more likely to
238 	 * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
239 	 * is why we include only movable, highmem and FS/IO pages.
240 	 * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
241 	 * we account it too.
242 	 */
243 	if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
244 		return;
245 
246 	/*
247 	 * If we got here with no pages scanned, then that is an indicator
248 	 * that reclaimer was unable to find any shrinkable LRUs at the
249 	 * current scanning depth. But it does not mean that we should
250 	 * report the critical pressure, yet. If the scanning priority
251 	 * (scanning depth) goes too high (deep), we will be notified
252 	 * through vmpressure_prio(). But so far, keep calm.
253 	 */
254 	if (!scanned)
255 		return;
256 
257 	if (tree) {
258 		spin_lock(&vmpr->sr_lock);
259 		scanned = vmpr->tree_scanned += scanned;
260 		vmpr->tree_reclaimed += reclaimed;
261 		spin_unlock(&vmpr->sr_lock);
262 
263 		if (scanned < vmpressure_win)
264 			return;
265 		schedule_work(&vmpr->work);
266 	} else {
267 		enum vmpressure_levels level;
268 
269 		/* For now, no users for root-level efficiency */
270 		if (!memcg || memcg == root_mem_cgroup)
271 			return;
272 
273 		spin_lock(&vmpr->sr_lock);
274 		scanned = vmpr->scanned += scanned;
275 		reclaimed = vmpr->reclaimed += reclaimed;
276 		if (scanned < vmpressure_win) {
277 			spin_unlock(&vmpr->sr_lock);
278 			return;
279 		}
280 		vmpr->scanned = vmpr->reclaimed = 0;
281 		spin_unlock(&vmpr->sr_lock);
282 
283 		level = vmpressure_calc_level(scanned, reclaimed);
284 
285 		if (level > VMPRESSURE_LOW) {
286 			/*
287 			 * Let the socket buffer allocator know that
288 			 * we are having trouble reclaiming LRU pages.
289 			 *
290 			 * For hysteresis keep the pressure state
291 			 * asserted for a second in which subsequent
292 			 * pressure events can occur.
293 			 */
294 			memcg->socket_pressure = jiffies + HZ;
295 		}
296 	}
297 }
298 
299 /**
300  * vmpressure_prio() - Account memory pressure through reclaimer priority level
301  * @gfp:	reclaimer's gfp mask
302  * @memcg:	cgroup memory controller handle
303  * @prio:	reclaimer's priority
304  *
305  * This function should be called from the reclaim path every time when
306  * the vmscan's reclaiming priority (scanning depth) changes.
307  *
308  * This function does not return any value.
309  */
310 void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
311 {
312 	/*
313 	 * We only use prio for accounting critical level. For more info
314 	 * see comment for vmpressure_level_critical_prio variable above.
315 	 */
316 	if (prio > vmpressure_level_critical_prio)
317 		return;
318 
319 	/*
320 	 * OK, the prio is below the threshold, updating vmpressure
321 	 * information before shrinker dives into long shrinking of long
322 	 * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
323 	 * to the vmpressure() basically means that we signal 'critical'
324 	 * level.
325 	 */
326 	vmpressure(gfp, memcg, true, vmpressure_win, 0);
327 }
328 
329 /**
330  * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
331  * @memcg:	memcg that is interested in vmpressure notifications
332  * @eventfd:	eventfd context to link notifications with
333  * @args:	event arguments (used to set up a pressure level threshold)
334  *
335  * This function associates eventfd context with the vmpressure
336  * infrastructure, so that the notifications will be delivered to the
337  * @eventfd. The @args parameter is a string that denotes pressure level
338  * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
339  * "critical").
340  *
341  * To be used as memcg event method.
342  */
343 int vmpressure_register_event(struct mem_cgroup *memcg,
344 			      struct eventfd_ctx *eventfd, const char *args)
345 {
346 	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
347 	struct vmpressure_event *ev;
348 	int level;
349 
350 	for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
351 		if (!strcmp(vmpressure_str_levels[level], args))
352 			break;
353 	}
354 
355 	if (level >= VMPRESSURE_NUM_LEVELS)
356 		return -EINVAL;
357 
358 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
359 	if (!ev)
360 		return -ENOMEM;
361 
362 	ev->efd = eventfd;
363 	ev->level = level;
364 
365 	mutex_lock(&vmpr->events_lock);
366 	list_add(&ev->node, &vmpr->events);
367 	mutex_unlock(&vmpr->events_lock);
368 
369 	return 0;
370 }
371 
372 /**
373  * vmpressure_unregister_event() - Unbind eventfd from vmpressure
374  * @memcg:	memcg handle
375  * @eventfd:	eventfd context that was used to link vmpressure with the @cg
376  *
377  * This function does internal manipulations to detach the @eventfd from
378  * the vmpressure notifications, and then frees internal resources
379  * associated with the @eventfd (but the @eventfd itself is not freed).
380  *
381  * To be used as memcg event method.
382  */
383 void vmpressure_unregister_event(struct mem_cgroup *memcg,
384 				 struct eventfd_ctx *eventfd)
385 {
386 	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
387 	struct vmpressure_event *ev;
388 
389 	mutex_lock(&vmpr->events_lock);
390 	list_for_each_entry(ev, &vmpr->events, node) {
391 		if (ev->efd != eventfd)
392 			continue;
393 		list_del(&ev->node);
394 		kfree(ev);
395 		break;
396 	}
397 	mutex_unlock(&vmpr->events_lock);
398 }
399 
400 /**
401  * vmpressure_init() - Initialize vmpressure control structure
402  * @vmpr:	Structure to be initialized
403  *
404  * This function should be called on every allocated vmpressure structure
405  * before any usage.
406  */
407 void vmpressure_init(struct vmpressure *vmpr)
408 {
409 	spin_lock_init(&vmpr->sr_lock);
410 	mutex_init(&vmpr->events_lock);
411 	INIT_LIST_HEAD(&vmpr->events);
412 	INIT_WORK(&vmpr->work, vmpressure_work_fn);
413 }
414 
415 /**
416  * vmpressure_cleanup() - shuts down vmpressure control structure
417  * @vmpr:	Structure to be cleaned up
418  *
419  * This function should be called before the structure in which it is
420  * embedded is cleaned up.
421  */
422 void vmpressure_cleanup(struct vmpressure *vmpr)
423 {
424 	/*
425 	 * Make sure there is no pending work before eventfd infrastructure
426 	 * goes away.
427 	 */
428 	flush_work(&vmpr->work);
429 }
430