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Anton Vorontsov70ddf632013-04-29 15:08:31 -07001/*
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 */
40static 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 */
48static const unsigned int vmpressure_level_med = 60;
49static 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 */
70static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);
71
72static struct vmpressure *work_to_vmpressure(struct work_struct *work)
73{
74 return container_of(work, struct vmpressure, work);
75}
76
77static struct vmpressure *cg_to_vmpressure(struct cgroup *cg)
78{
79 return css_to_vmpressure(cgroup_subsys_state(cg, mem_cgroup_subsys_id));
80}
81
82static 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
93enum vmpressure_levels {
94 VMPRESSURE_LOW = 0,
95 VMPRESSURE_MEDIUM,
96 VMPRESSURE_CRITICAL,
97 VMPRESSURE_NUM_LEVELS,
98};
99
100static const char * const vmpressure_str_levels[] = {
101 [VMPRESSURE_LOW] = "low",
102 [VMPRESSURE_MEDIUM] = "medium",
103 [VMPRESSURE_CRITICAL] = "critical",
104};
105
106static 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
115static 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
137struct vmpressure_event {
138 struct eventfd_ctx *efd;
139 enum vmpressure_levels level;
140 struct list_head node;
141};
142
143static 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
166static 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
Michal Hocko22f20202013-07-31 13:53:48 -0700183 spin_lock(&vmpr->sr_lock);
Anton Vorontsov70ddf632013-04-29 15:08:31 -0700184 scanned = vmpr->scanned;
185 reclaimed = vmpr->reclaimed;
186 vmpr->scanned = 0;
187 vmpr->reclaimed = 0;
Michal Hocko22f20202013-07-31 13:53:48 -0700188 spin_unlock(&vmpr->sr_lock);
Anton Vorontsov70ddf632013-04-29 15:08:31 -0700189
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 */
213void 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
Michal Hocko22f20202013-07-31 13:53:48 -0700243 spin_lock(&vmpr->sr_lock);
Anton Vorontsov70ddf632013-04-29 15:08:31 -0700244 vmpr->scanned += scanned;
245 vmpr->reclaimed += reclaimed;
246 scanned = vmpr->scanned;
Michal Hocko22f20202013-07-31 13:53:48 -0700247 spin_unlock(&vmpr->sr_lock);
Anton Vorontsov70ddf632013-04-29 15:08:31 -0700248
Michal Hocko8e0ed442013-07-31 13:53:50 -0700249 if (scanned < vmpressure_win)
Anton Vorontsov70ddf632013-04-29 15:08:31 -0700250 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 */
265void 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 */
301int 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 */
344void 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 */
368void vmpressure_init(struct vmpressure *vmpr)
369{
Michal Hocko22f20202013-07-31 13:53:48 -0700370 spin_lock_init(&vmpr->sr_lock);
Anton Vorontsov70ddf632013-04-29 15:08:31 -0700371 mutex_init(&vmpr->events_lock);
372 INIT_LIST_HEAD(&vmpr->events);
373 INIT_WORK(&vmpr->work, vmpressure_work_fn);
374}
Michal Hocko33cb8762013-07-31 13:53:51 -0700375
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 */
383void 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}