]> git.proxmox.com Git - mirror_ubuntu-bionic-kernel.git/blob - mm/vmpressure.c
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
[mirror_ubuntu-bionic-kernel.git] / mm / vmpressure.c
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 }