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