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d2912cb1 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
70ddf637 AV |
2 | /* |
3 | * Linux VM pressure | |
4 | * | |
5 | * Copyright 2012 Linaro Ltd. | |
6 | * Anton Vorontsov <anton.vorontsov@linaro.org> | |
7 | * | |
8 | * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro, | |
9 | * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg. | |
70ddf637 AV |
10 | */ |
11 | ||
12 | #include <linux/cgroup.h> | |
13 | #include <linux/fs.h> | |
14 | #include <linux/log2.h> | |
15 | #include <linux/sched.h> | |
16 | #include <linux/mm.h> | |
17 | #include <linux/vmstat.h> | |
18 | #include <linux/eventfd.h> | |
1ff6bbfd | 19 | #include <linux/slab.h> |
70ddf637 AV |
20 | #include <linux/swap.h> |
21 | #include <linux/printk.h> | |
22 | #include <linux/vmpressure.h> | |
23 | ||
24 | /* | |
25 | * The window size (vmpressure_win) is the number of scanned pages before | |
26 | * we try to analyze scanned/reclaimed ratio. So the window is used as a | |
27 | * rate-limit tunable for the "low" level notification, and also for | |
28 | * averaging the ratio for medium/critical levels. Using small window | |
29 | * sizes can cause lot of false positives, but too big window size will | |
30 | * delay the notifications. | |
31 | * | |
32 | * As the vmscan reclaimer logic works with chunks which are multiple of | |
33 | * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well. | |
34 | * | |
35 | * TODO: Make the window size depend on machine size, as we do for vmstat | |
36 | * thresholds. Currently we set it to 512 pages (2MB for 4KB pages). | |
37 | */ | |
38 | static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16; | |
39 | ||
40 | /* | |
41 | * These thresholds are used when we account memory pressure through | |
42 | * scanned/reclaimed ratio. The current values were chosen empirically. In | |
43 | * essence, they are percents: the higher the value, the more number | |
44 | * unsuccessful reclaims there were. | |
45 | */ | |
46 | static const unsigned int vmpressure_level_med = 60; | |
47 | static const unsigned int vmpressure_level_critical = 95; | |
48 | ||
49 | /* | |
50 | * When there are too little pages left to scan, vmpressure() may miss the | |
51 | * critical pressure as number of pages will be less than "window size". | |
52 | * However, in that case the vmscan priority will raise fast as the | |
53 | * reclaimer will try to scan LRUs more deeply. | |
54 | * | |
55 | * The vmscan logic considers these special priorities: | |
56 | * | |
57 | * prio == DEF_PRIORITY (12): reclaimer starts with that value | |
58 | * prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed | |
59 | * prio == 0 : close to OOM, kernel scans every page in an lru | |
60 | * | |
61 | * Any value in this range is acceptable for this tunable (i.e. from 12 to | |
62 | * 0). Current value for the vmpressure_level_critical_prio is chosen | |
63 | * empirically, but the number, in essence, means that we consider | |
64 | * critical level when scanning depth is ~10% of the lru size (vmscan | |
65 | * scans 'lru_size >> prio' pages, so it is actually 12.5%, or one | |
66 | * eights). | |
67 | */ | |
68 | static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10); | |
69 | ||
70 | static struct vmpressure *work_to_vmpressure(struct work_struct *work) | |
71 | { | |
72 | return container_of(work, struct vmpressure, work); | |
73 | } | |
74 | ||
70ddf637 AV |
75 | static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr) |
76 | { | |
182446d0 TH |
77 | struct cgroup_subsys_state *css = vmpressure_to_css(vmpr); |
78 | struct mem_cgroup *memcg = mem_cgroup_from_css(css); | |
70ddf637 AV |
79 | |
80 | memcg = parent_mem_cgroup(memcg); | |
81 | if (!memcg) | |
82 | return NULL; | |
83 | return memcg_to_vmpressure(memcg); | |
84 | } | |
85 | ||
86 | enum vmpressure_levels { | |
87 | VMPRESSURE_LOW = 0, | |
88 | VMPRESSURE_MEDIUM, | |
89 | VMPRESSURE_CRITICAL, | |
90 | VMPRESSURE_NUM_LEVELS, | |
91 | }; | |
92 | ||
b6bb9811 DR |
93 | enum vmpressure_modes { |
94 | VMPRESSURE_NO_PASSTHROUGH = 0, | |
95 | VMPRESSURE_HIERARCHY, | |
96 | VMPRESSURE_LOCAL, | |
97 | VMPRESSURE_NUM_MODES, | |
98 | }; | |
99 | ||
70ddf637 AV |
100 | static const char * const vmpressure_str_levels[] = { |
101 | [VMPRESSURE_LOW] = "low", | |
102 | [VMPRESSURE_MEDIUM] = "medium", | |
103 | [VMPRESSURE_CRITICAL] = "critical", | |
104 | }; | |
105 | ||
b6bb9811 DR |
106 | static const char * const vmpressure_str_modes[] = { |
107 | [VMPRESSURE_NO_PASSTHROUGH] = "default", | |
108 | [VMPRESSURE_HIERARCHY] = "hierarchy", | |
109 | [VMPRESSURE_LOCAL] = "local", | |
110 | }; | |
111 | ||
70ddf637 AV |
112 | static enum vmpressure_levels vmpressure_level(unsigned long pressure) |
113 | { | |
114 | if (pressure >= vmpressure_level_critical) | |
115 | return VMPRESSURE_CRITICAL; | |
116 | else if (pressure >= vmpressure_level_med) | |
117 | return VMPRESSURE_MEDIUM; | |
118 | return VMPRESSURE_LOW; | |
119 | } | |
120 | ||
121 | static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned, | |
122 | unsigned long reclaimed) | |
123 | { | |
124 | unsigned long scale = scanned + reclaimed; | |
e1587a49 | 125 | unsigned long pressure = 0; |
70ddf637 | 126 | |
e1587a49 | 127 | /* |
d7143e31 | 128 | * reclaimed can be greater than scanned for things such as reclaimed |
129 | * slab pages. shrink_node() just adds reclaimed pages without a | |
130 | * related increment to scanned pages. | |
e1587a49 VM |
131 | */ |
132 | if (reclaimed >= scanned) | |
133 | goto out; | |
70ddf637 AV |
134 | /* |
135 | * We calculate the ratio (in percents) of how many pages were | |
136 | * scanned vs. reclaimed in a given time frame (window). Note that | |
137 | * time is in VM reclaimer's "ticks", i.e. number of pages | |
138 | * scanned. This makes it possible to set desired reaction time | |
139 | * and serves as a ratelimit. | |
140 | */ | |
141 | pressure = scale - (reclaimed * scale / scanned); | |
142 | pressure = pressure * 100 / scale; | |
143 | ||
e1587a49 | 144 | out: |
70ddf637 AV |
145 | pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure, |
146 | scanned, reclaimed); | |
147 | ||
148 | return vmpressure_level(pressure); | |
149 | } | |
150 | ||
151 | struct vmpressure_event { | |
152 | struct eventfd_ctx *efd; | |
153 | enum vmpressure_levels level; | |
b6bb9811 | 154 | enum vmpressure_modes mode; |
70ddf637 AV |
155 | struct list_head node; |
156 | }; | |
157 | ||
158 | static bool vmpressure_event(struct vmpressure *vmpr, | |
b6bb9811 DR |
159 | const enum vmpressure_levels level, |
160 | bool ancestor, bool signalled) | |
70ddf637 AV |
161 | { |
162 | struct vmpressure_event *ev; | |
b6bb9811 | 163 | bool ret = false; |
70ddf637 | 164 | |
70ddf637 | 165 | mutex_lock(&vmpr->events_lock); |
70ddf637 | 166 | list_for_each_entry(ev, &vmpr->events, node) { |
b6bb9811 DR |
167 | if (ancestor && ev->mode == VMPRESSURE_LOCAL) |
168 | continue; | |
169 | if (signalled && ev->mode == VMPRESSURE_NO_PASSTHROUGH) | |
170 | continue; | |
171 | if (level < ev->level) | |
172 | continue; | |
173 | eventfd_signal(ev->efd, 1); | |
174 | ret = true; | |
70ddf637 | 175 | } |
70ddf637 AV |
176 | mutex_unlock(&vmpr->events_lock); |
177 | ||
b6bb9811 | 178 | return ret; |
70ddf637 AV |
179 | } |
180 | ||
181 | static void vmpressure_work_fn(struct work_struct *work) | |
182 | { | |
183 | struct vmpressure *vmpr = work_to_vmpressure(work); | |
184 | unsigned long scanned; | |
185 | unsigned long reclaimed; | |
8e8ae645 | 186 | enum vmpressure_levels level; |
b6bb9811 DR |
187 | bool ancestor = false; |
188 | bool signalled = false; | |
70ddf637 | 189 | |
91b57191 | 190 | spin_lock(&vmpr->sr_lock); |
70ddf637 AV |
191 | /* |
192 | * Several contexts might be calling vmpressure(), so it is | |
193 | * possible that the work was rescheduled again before the old | |
194 | * work context cleared the counters. In that case we will run | |
195 | * just after the old work returns, but then scanned might be zero | |
196 | * here. No need for any locks here since we don't care if | |
197 | * vmpr->reclaimed is in sync. | |
198 | */ | |
8e8ae645 | 199 | scanned = vmpr->tree_scanned; |
91b57191 AM |
200 | if (!scanned) { |
201 | spin_unlock(&vmpr->sr_lock); | |
70ddf637 | 202 | return; |
91b57191 | 203 | } |
70ddf637 | 204 | |
8e8ae645 JW |
205 | reclaimed = vmpr->tree_reclaimed; |
206 | vmpr->tree_scanned = 0; | |
207 | vmpr->tree_reclaimed = 0; | |
22f2020f | 208 | spin_unlock(&vmpr->sr_lock); |
70ddf637 | 209 | |
8e8ae645 JW |
210 | level = vmpressure_calc_level(scanned, reclaimed); |
211 | ||
70ddf637 | 212 | do { |
b6bb9811 DR |
213 | if (vmpressure_event(vmpr, level, ancestor, signalled)) |
214 | signalled = true; | |
215 | ancestor = true; | |
70ddf637 AV |
216 | } while ((vmpr = vmpressure_parent(vmpr))); |
217 | } | |
218 | ||
219 | /** | |
220 | * vmpressure() - Account memory pressure through scanned/reclaimed ratio | |
221 | * @gfp: reclaimer's gfp mask | |
222 | * @memcg: cgroup memory controller handle | |
8e8ae645 | 223 | * @tree: legacy subtree mode |
70ddf637 AV |
224 | * @scanned: number of pages scanned |
225 | * @reclaimed: number of pages reclaimed | |
226 | * | |
227 | * This function should be called from the vmscan reclaim path to account | |
228 | * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw | |
229 | * pressure index is then further refined and averaged over time. | |
230 | * | |
8e8ae645 JW |
231 | * If @tree is set, vmpressure is in traditional userspace reporting |
232 | * mode: @memcg is considered the pressure root and userspace is | |
233 | * notified of the entire subtree's reclaim efficiency. | |
234 | * | |
235 | * If @tree is not set, reclaim efficiency is recorded for @memcg, and | |
236 | * only in-kernel users are notified. | |
237 | * | |
70ddf637 AV |
238 | * This function does not return any value. |
239 | */ | |
8e8ae645 | 240 | void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree, |
70ddf637 AV |
241 | unsigned long scanned, unsigned long reclaimed) |
242 | { | |
243 | struct vmpressure *vmpr = memcg_to_vmpressure(memcg); | |
244 | ||
245 | /* | |
246 | * Here we only want to account pressure that userland is able to | |
247 | * help us with. For example, suppose that DMA zone is under | |
248 | * pressure; if we notify userland about that kind of pressure, | |
249 | * then it will be mostly a waste as it will trigger unnecessary | |
250 | * freeing of memory by userland (since userland is more likely to | |
251 | * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That | |
252 | * is why we include only movable, highmem and FS/IO pages. | |
253 | * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so | |
254 | * we account it too. | |
255 | */ | |
256 | if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS))) | |
257 | return; | |
258 | ||
259 | /* | |
260 | * If we got here with no pages scanned, then that is an indicator | |
261 | * that reclaimer was unable to find any shrinkable LRUs at the | |
262 | * current scanning depth. But it does not mean that we should | |
263 | * report the critical pressure, yet. If the scanning priority | |
264 | * (scanning depth) goes too high (deep), we will be notified | |
265 | * through vmpressure_prio(). But so far, keep calm. | |
266 | */ | |
267 | if (!scanned) | |
268 | return; | |
269 | ||
8e8ae645 JW |
270 | if (tree) { |
271 | spin_lock(&vmpr->sr_lock); | |
3c1da7be | 272 | scanned = vmpr->tree_scanned += scanned; |
8e8ae645 | 273 | vmpr->tree_reclaimed += reclaimed; |
8e8ae645 | 274 | spin_unlock(&vmpr->sr_lock); |
70ddf637 | 275 | |
8e8ae645 JW |
276 | if (scanned < vmpressure_win) |
277 | return; | |
278 | schedule_work(&vmpr->work); | |
279 | } else { | |
280 | enum vmpressure_levels level; | |
281 | ||
282 | /* For now, no users for root-level efficiency */ | |
686739f6 | 283 | if (!memcg || memcg == root_mem_cgroup) |
8e8ae645 JW |
284 | return; |
285 | ||
286 | spin_lock(&vmpr->sr_lock); | |
287 | scanned = vmpr->scanned += scanned; | |
288 | reclaimed = vmpr->reclaimed += reclaimed; | |
289 | if (scanned < vmpressure_win) { | |
290 | spin_unlock(&vmpr->sr_lock); | |
291 | return; | |
292 | } | |
293 | vmpr->scanned = vmpr->reclaimed = 0; | |
294 | spin_unlock(&vmpr->sr_lock); | |
295 | ||
296 | level = vmpressure_calc_level(scanned, reclaimed); | |
297 | ||
298 | if (level > VMPRESSURE_LOW) { | |
299 | /* | |
300 | * Let the socket buffer allocator know that | |
301 | * we are having trouble reclaiming LRU pages. | |
302 | * | |
303 | * For hysteresis keep the pressure state | |
304 | * asserted for a second in which subsequent | |
305 | * pressure events can occur. | |
306 | */ | |
307 | memcg->socket_pressure = jiffies + HZ; | |
308 | } | |
309 | } | |
70ddf637 AV |
310 | } |
311 | ||
312 | /** | |
313 | * vmpressure_prio() - Account memory pressure through reclaimer priority level | |
314 | * @gfp: reclaimer's gfp mask | |
315 | * @memcg: cgroup memory controller handle | |
316 | * @prio: reclaimer's priority | |
317 | * | |
318 | * This function should be called from the reclaim path every time when | |
319 | * the vmscan's reclaiming priority (scanning depth) changes. | |
320 | * | |
321 | * This function does not return any value. | |
322 | */ | |
323 | void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio) | |
324 | { | |
325 | /* | |
326 | * We only use prio for accounting critical level. For more info | |
327 | * see comment for vmpressure_level_critical_prio variable above. | |
328 | */ | |
329 | if (prio > vmpressure_level_critical_prio) | |
330 | return; | |
331 | ||
332 | /* | |
333 | * OK, the prio is below the threshold, updating vmpressure | |
334 | * information before shrinker dives into long shrinking of long | |
335 | * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0 | |
336 | * to the vmpressure() basically means that we signal 'critical' | |
337 | * level. | |
338 | */ | |
8e8ae645 | 339 | vmpressure(gfp, memcg, true, vmpressure_win, 0); |
70ddf637 AV |
340 | } |
341 | ||
b6bb9811 DR |
342 | #define MAX_VMPRESSURE_ARGS_LEN (strlen("critical") + strlen("hierarchy") + 2) |
343 | ||
70ddf637 AV |
344 | /** |
345 | * vmpressure_register_event() - Bind vmpressure notifications to an eventfd | |
59b6f873 | 346 | * @memcg: memcg that is interested in vmpressure notifications |
70ddf637 | 347 | * @eventfd: eventfd context to link notifications with |
b6bb9811 | 348 | * @args: event arguments (pressure level threshold, optional mode) |
70ddf637 AV |
349 | * |
350 | * This function associates eventfd context with the vmpressure | |
351 | * infrastructure, so that the notifications will be delivered to the | |
b6bb9811 DR |
352 | * @eventfd. The @args parameter is a comma-delimited string that denotes a |
353 | * pressure level threshold (one of vmpressure_str_levels, i.e. "low", "medium", | |
354 | * or "critical") and an optional mode (one of vmpressure_str_modes, i.e. | |
355 | * "hierarchy" or "local"). | |
70ddf637 | 356 | * |
347c4a87 | 357 | * To be used as memcg event method. |
518a8671 DC |
358 | * |
359 | * Return: 0 on success, -ENOMEM on memory failure or -EINVAL if @args could | |
360 | * not be parsed. | |
70ddf637 | 361 | */ |
59b6f873 | 362 | int vmpressure_register_event(struct mem_cgroup *memcg, |
347c4a87 | 363 | struct eventfd_ctx *eventfd, const char *args) |
70ddf637 | 364 | { |
59b6f873 | 365 | struct vmpressure *vmpr = memcg_to_vmpressure(memcg); |
70ddf637 | 366 | struct vmpressure_event *ev; |
b6bb9811 | 367 | enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH; |
518a8671 | 368 | enum vmpressure_levels level; |
b6bb9811 DR |
369 | char *spec, *spec_orig; |
370 | char *token; | |
371 | int ret = 0; | |
372 | ||
d62ff365 | 373 | spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL); |
b6bb9811 DR |
374 | if (!spec) { |
375 | ret = -ENOMEM; | |
376 | goto out; | |
377 | } | |
70ddf637 | 378 | |
b6bb9811 DR |
379 | /* Find required level */ |
380 | token = strsep(&spec, ","); | |
518a8671 DC |
381 | ret = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token); |
382 | if (ret < 0) | |
b6bb9811 | 383 | goto out; |
518a8671 | 384 | level = ret; |
70ddf637 | 385 | |
b6bb9811 DR |
386 | /* Find optional mode */ |
387 | token = strsep(&spec, ","); | |
388 | if (token) { | |
518a8671 DC |
389 | ret = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token); |
390 | if (ret < 0) | |
b6bb9811 | 391 | goto out; |
518a8671 | 392 | mode = ret; |
b6bb9811 | 393 | } |
70ddf637 AV |
394 | |
395 | ev = kzalloc(sizeof(*ev), GFP_KERNEL); | |
b6bb9811 DR |
396 | if (!ev) { |
397 | ret = -ENOMEM; | |
398 | goto out; | |
399 | } | |
70ddf637 AV |
400 | |
401 | ev->efd = eventfd; | |
402 | ev->level = level; | |
b6bb9811 | 403 | ev->mode = mode; |
70ddf637 AV |
404 | |
405 | mutex_lock(&vmpr->events_lock); | |
406 | list_add(&ev->node, &vmpr->events); | |
407 | mutex_unlock(&vmpr->events_lock); | |
518a8671 | 408 | ret = 0; |
b6bb9811 DR |
409 | out: |
410 | kfree(spec_orig); | |
411 | return ret; | |
70ddf637 AV |
412 | } |
413 | ||
414 | /** | |
415 | * vmpressure_unregister_event() - Unbind eventfd from vmpressure | |
59b6f873 | 416 | * @memcg: memcg handle |
70ddf637 AV |
417 | * @eventfd: eventfd context that was used to link vmpressure with the @cg |
418 | * | |
419 | * This function does internal manipulations to detach the @eventfd from | |
420 | * the vmpressure notifications, and then frees internal resources | |
421 | * associated with the @eventfd (but the @eventfd itself is not freed). | |
422 | * | |
347c4a87 | 423 | * To be used as memcg event method. |
70ddf637 | 424 | */ |
59b6f873 | 425 | void vmpressure_unregister_event(struct mem_cgroup *memcg, |
70ddf637 AV |
426 | struct eventfd_ctx *eventfd) |
427 | { | |
59b6f873 | 428 | struct vmpressure *vmpr = memcg_to_vmpressure(memcg); |
70ddf637 AV |
429 | struct vmpressure_event *ev; |
430 | ||
431 | mutex_lock(&vmpr->events_lock); | |
432 | list_for_each_entry(ev, &vmpr->events, node) { | |
433 | if (ev->efd != eventfd) | |
434 | continue; | |
435 | list_del(&ev->node); | |
436 | kfree(ev); | |
437 | break; | |
438 | } | |
439 | mutex_unlock(&vmpr->events_lock); | |
440 | } | |
441 | ||
442 | /** | |
443 | * vmpressure_init() - Initialize vmpressure control structure | |
444 | * @vmpr: Structure to be initialized | |
445 | * | |
446 | * This function should be called on every allocated vmpressure structure | |
447 | * before any usage. | |
448 | */ | |
449 | void vmpressure_init(struct vmpressure *vmpr) | |
450 | { | |
22f2020f | 451 | spin_lock_init(&vmpr->sr_lock); |
70ddf637 AV |
452 | mutex_init(&vmpr->events_lock); |
453 | INIT_LIST_HEAD(&vmpr->events); | |
454 | INIT_WORK(&vmpr->work, vmpressure_work_fn); | |
455 | } | |
33cb876e MH |
456 | |
457 | /** | |
458 | * vmpressure_cleanup() - shuts down vmpressure control structure | |
459 | * @vmpr: Structure to be cleaned up | |
460 | * | |
461 | * This function should be called before the structure in which it is | |
462 | * embedded is cleaned up. | |
463 | */ | |
464 | void vmpressure_cleanup(struct vmpressure *vmpr) | |
465 | { | |
466 | /* | |
467 | * Make sure there is no pending work before eventfd infrastructure | |
468 | * goes away. | |
469 | */ | |
470 | flush_work(&vmpr->work); | |
471 | } |