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 */
41static 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 */
49static const unsigned int vmpressure_level_med = 60;
50static 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 */
71static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);
72
73static struct vmpressure *work_to_vmpressure(struct work_struct *work)
74{
75 return container_of(work, struct vmpressure, work);
76}
77
78static 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
89enum vmpressure_levels {
90 VMPRESSURE_LOW = 0,
91 VMPRESSURE_MEDIUM,
92 VMPRESSURE_CRITICAL,
93 VMPRESSURE_NUM_LEVELS,
94};
95
96enum vmpressure_modes {
97 VMPRESSURE_NO_PASSTHROUGH = 0,
98 VMPRESSURE_HIERARCHY,
99 VMPRESSURE_LOCAL,
100 VMPRESSURE_NUM_MODES,
101};
102
103static const char * const vmpressure_str_levels[] = {
104 [VMPRESSURE_LOW] = "low",
105 [VMPRESSURE_MEDIUM] = "medium",
106 [VMPRESSURE_CRITICAL] = "critical",
107};
108
109static const char * const vmpressure_str_modes[] = {
110 [VMPRESSURE_NO_PASSTHROUGH] = "default",
111 [VMPRESSURE_HIERARCHY] = "hierarchy",
112 [VMPRESSURE_LOCAL] = "local",
113};
114
115static enum vmpressure_levels vmpressure_level(unsigned long pressure)
116{
117 if (pressure >= vmpressure_level_critical)
118 return VMPRESSURE_CRITICAL;
119 else if (pressure >= vmpressure_level_med)
120 return VMPRESSURE_MEDIUM;
121 return VMPRESSURE_LOW;
122}
123
124static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
125 unsigned long reclaimed)
126{
127 unsigned long scale = scanned + reclaimed;
128 unsigned long pressure = 0;
129
130 /*
131 * reclaimed can be greater than scanned for things such as reclaimed
132 * slab pages. shrink_node() just adds reclaimed pages without a
133 * related increment to scanned pages.
134 */
135 if (reclaimed >= scanned)
136 goto out;
137 /*
138 * We calculate the ratio (in percents) of how many pages were
139 * scanned vs. reclaimed in a given time frame (window). Note that
140 * time is in VM reclaimer's "ticks", i.e. number of pages
141 * scanned. This makes it possible to set desired reaction time
142 * and serves as a ratelimit.
143 */
144 pressure = scale - (reclaimed * scale / scanned);
145 pressure = pressure * 100 / scale;
146
147out:
148 pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure,
149 scanned, reclaimed);
150
151 return vmpressure_level(pressure);
152}
153
154struct vmpressure_event {
155 struct eventfd_ctx *efd;
156 enum vmpressure_levels level;
157 enum vmpressure_modes mode;
158 struct list_head node;
159};
160
161static bool vmpressure_event(struct vmpressure *vmpr,
162 const enum vmpressure_levels level,
163 bool ancestor, bool signalled)
164{
165 struct vmpressure_event *ev;
166 bool ret = false;
167
168 mutex_lock(&vmpr->events_lock);
169 list_for_each_entry(ev, &vmpr->events, node) {
170 if (ancestor && ev->mode == VMPRESSURE_LOCAL)
171 continue;
172 if (signalled && ev->mode == VMPRESSURE_NO_PASSTHROUGH)
173 continue;
174 if (level < ev->level)
175 continue;
176 eventfd_signal(ev->efd, 1);
177 ret = true;
178 }
179 mutex_unlock(&vmpr->events_lock);
180
181 return ret;
182}
183
184static void vmpressure_work_fn(struct work_struct *work)
185{
186 struct vmpressure *vmpr = work_to_vmpressure(work);
187 unsigned long scanned;
188 unsigned long reclaimed;
189 enum vmpressure_levels level;
190 bool ancestor = false;
191 bool signalled = false;
192
193 spin_lock(&vmpr->sr_lock);
194 /*
195 * Several contexts might be calling vmpressure(), so it is
196 * possible that the work was rescheduled again before the old
197 * work context cleared the counters. In that case we will run
198 * just after the old work returns, but then scanned might be zero
199 * here. No need for any locks here since we don't care if
200 * vmpr->reclaimed is in sync.
201 */
202 scanned = vmpr->tree_scanned;
203 if (!scanned) {
204 spin_unlock(&vmpr->sr_lock);
205 return;
206 }
207
208 reclaimed = vmpr->tree_reclaimed;
209 vmpr->tree_scanned = 0;
210 vmpr->tree_reclaimed = 0;
211 spin_unlock(&vmpr->sr_lock);
212
213 level = vmpressure_calc_level(scanned, reclaimed);
214
215 do {
216 if (vmpressure_event(vmpr, level, ancestor, signalled))
217 signalled = true;
218 ancestor = true;
219 } while ((vmpr = vmpressure_parent(vmpr)));
220}
221
222/**
223 * vmpressure() - Account memory pressure through scanned/reclaimed ratio
224 * @gfp: reclaimer's gfp mask
225 * @memcg: cgroup memory controller handle
226 * @tree: legacy subtree mode
227 * @scanned: number of pages scanned
228 * @reclaimed: number of pages reclaimed
229 *
230 * This function should be called from the vmscan reclaim path to account
231 * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
232 * pressure index is then further refined and averaged over time.
233 *
234 * If @tree is set, vmpressure is in traditional userspace reporting
235 * mode: @memcg is considered the pressure root and userspace is
236 * notified of the entire subtree's reclaim efficiency.
237 *
238 * If @tree is not set, reclaim efficiency is recorded for @memcg, and
239 * only in-kernel users are notified.
240 *
241 * This function does not return any value.
242 */
243void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
244 unsigned long scanned, unsigned long reclaimed)
245{
246 struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
247
248 /*
249 * Here we only want to account pressure that userland is able to
250 * help us with. For example, suppose that DMA zone is under
251 * pressure; if we notify userland about that kind of pressure,
252 * then it will be mostly a waste as it will trigger unnecessary
253 * freeing of memory by userland (since userland is more likely to
254 * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
255 * is why we include only movable, highmem and FS/IO pages.
256 * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
257 * we account it too.
258 */
259 if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
260 return;
261
262 /*
263 * If we got here with no pages scanned, then that is an indicator
264 * that reclaimer was unable to find any shrinkable LRUs at the
265 * current scanning depth. But it does not mean that we should
266 * report the critical pressure, yet. If the scanning priority
267 * (scanning depth) goes too high (deep), we will be notified
268 * through vmpressure_prio(). But so far, keep calm.
269 */
270 if (!scanned)
271 return;
272
273 if (tree) {
274 spin_lock(&vmpr->sr_lock);
275 scanned = vmpr->tree_scanned += scanned;
276 vmpr->tree_reclaimed += reclaimed;
277 spin_unlock(&vmpr->sr_lock);
278
279 if (scanned < vmpressure_win)
280 return;
281 schedule_work(&vmpr->work);
282 } else {
283 enum vmpressure_levels level;
284
285 /* For now, no users for root-level efficiency */
286 if (!memcg || memcg == root_mem_cgroup)
287 return;
288
289 spin_lock(&vmpr->sr_lock);
290 scanned = vmpr->scanned += scanned;
291 reclaimed = vmpr->reclaimed += reclaimed;
292 if (scanned < vmpressure_win) {
293 spin_unlock(&vmpr->sr_lock);
294 return;
295 }
296 vmpr->scanned = vmpr->reclaimed = 0;
297 spin_unlock(&vmpr->sr_lock);
298
299 level = vmpressure_calc_level(scanned, reclaimed);
300
301 if (level > VMPRESSURE_LOW) {
302 /*
303 * Let the socket buffer allocator know that
304 * we are having trouble reclaiming LRU pages.
305 *
306 * For hysteresis keep the pressure state
307 * asserted for a second in which subsequent
308 * pressure events can occur.
309 */
310 memcg->socket_pressure = jiffies + HZ;
311 }
312 }
313}
314
315/**
316 * vmpressure_prio() - Account memory pressure through reclaimer priority level
317 * @gfp: reclaimer's gfp mask
318 * @memcg: cgroup memory controller handle
319 * @prio: reclaimer's priority
320 *
321 * This function should be called from the reclaim path every time when
322 * the vmscan's reclaiming priority (scanning depth) changes.
323 *
324 * This function does not return any value.
325 */
326void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
327{
328 /*
329 * We only use prio for accounting critical level. For more info
330 * see comment for vmpressure_level_critical_prio variable above.
331 */
332 if (prio > vmpressure_level_critical_prio)
333 return;
334
335 /*
336 * OK, the prio is below the threshold, updating vmpressure
337 * information before shrinker dives into long shrinking of long
338 * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
339 * to the vmpressure() basically means that we signal 'critical'
340 * level.
341 */
342 vmpressure(gfp, memcg, true, vmpressure_win, 0);
343}
344
345#define MAX_VMPRESSURE_ARGS_LEN (strlen("critical") + strlen("hierarchy") + 2)
346
347/**
348 * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
349 * @memcg: memcg that is interested in vmpressure notifications
350 * @eventfd: eventfd context to link notifications with
351 * @args: event arguments (pressure level threshold, optional mode)
352 *
353 * This function associates eventfd context with the vmpressure
354 * infrastructure, so that the notifications will be delivered to the
355 * @eventfd. The @args parameter is a comma-delimited string that denotes a
356 * pressure level threshold (one of vmpressure_str_levels, i.e. "low", "medium",
357 * or "critical") and an optional mode (one of vmpressure_str_modes, i.e.
358 * "hierarchy" or "local").
359 *
360 * To be used as memcg event method.
361 */
362int vmpressure_register_event(struct mem_cgroup *memcg,
363 struct eventfd_ctx *eventfd, const char *args)
364{
365 struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
366 struct vmpressure_event *ev;
367 enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH;
368 enum vmpressure_levels level = -1;
369 char *spec, *spec_orig;
370 char *token;
371 int ret = 0;
372
373 spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
374 if (!spec) {
375 ret = -ENOMEM;
376 goto out;
377 }
378
379 /* Find required level */
380 token = strsep(&spec, ",");
381 level = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token);
382 if (level < 0) {
383 ret = level;
384 goto out;
385 }
386
387 /* Find optional mode */
388 token = strsep(&spec, ",");
389 if (token) {
390 mode = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token);
391 if (mode < 0) {
392 ret = mode;
393 goto out;
394 }
395 }
396
397 ev = kzalloc(sizeof(*ev), GFP_KERNEL);
398 if (!ev) {
399 ret = -ENOMEM;
400 goto out;
401 }
402
403 ev->efd = eventfd;
404 ev->level = level;
405 ev->mode = mode;
406
407 mutex_lock(&vmpr->events_lock);
408 list_add(&ev->node, &vmpr->events);
409 mutex_unlock(&vmpr->events_lock);
410out:
411 kfree(spec_orig);
412 return ret;
413}
414
415/**
416 * vmpressure_unregister_event() - Unbind eventfd from vmpressure
417 * @memcg: memcg handle
418 * @eventfd: eventfd context that was used to link vmpressure with the @cg
419 *
420 * This function does internal manipulations to detach the @eventfd from
421 * the vmpressure notifications, and then frees internal resources
422 * associated with the @eventfd (but the @eventfd itself is not freed).
423 *
424 * To be used as memcg event method.
425 */
426void vmpressure_unregister_event(struct mem_cgroup *memcg,
427 struct eventfd_ctx *eventfd)
428{
429 struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
430 struct vmpressure_event *ev;
431
432 mutex_lock(&vmpr->events_lock);
433 list_for_each_entry(ev, &vmpr->events, node) {
434 if (ev->efd != eventfd)
435 continue;
436 list_del(&ev->node);
437 kfree(ev);
438 break;
439 }
440 mutex_unlock(&vmpr->events_lock);
441}
442
443/**
444 * vmpressure_init() - Initialize vmpressure control structure
445 * @vmpr: Structure to be initialized
446 *
447 * This function should be called on every allocated vmpressure structure
448 * before any usage.
449 */
450void vmpressure_init(struct vmpressure *vmpr)
451{
452 spin_lock_init(&vmpr->sr_lock);
453 mutex_init(&vmpr->events_lock);
454 INIT_LIST_HEAD(&vmpr->events);
455 INIT_WORK(&vmpr->work, vmpressure_work_fn);
456}
457
458/**
459 * vmpressure_cleanup() - shuts down vmpressure control structure
460 * @vmpr: Structure to be cleaned up
461 *
462 * This function should be called before the structure in which it is
463 * embedded is cleaned up.
464 */
465void vmpressure_cleanup(struct vmpressure *vmpr)
466{
467 /*
468 * Make sure there is no pending work before eventfd infrastructure
469 * goes away.
470 */
471 flush_work(&vmpr->work);
472}
473