4 * Copyright 2012 Linaro Ltd.
5 * Anton Vorontsov <anton.vorontsov@linaro.org>
7 * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
8 * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
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.
15 #include <linux/cgroup.h>
17 #include <linux/log2.h>
18 #include <linux/sched.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>
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.
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.
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).
40 static const unsigned long vmpressure_win
= SWAP_CLUSTER_MAX
* 16;
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.
48 static const unsigned int vmpressure_level_med
= 60;
49 static const unsigned int vmpressure_level_critical
= 95;
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.
57 * The vmscan logic considers these special priorities:
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
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
70 static const unsigned int vmpressure_level_critical_prio
= ilog2(100 / 10);
72 static struct vmpressure
*work_to_vmpressure(struct work_struct
*work
)
74 return container_of(work
, struct vmpressure
, work
);
77 static struct vmpressure
*cg_to_vmpressure(struct cgroup
*cg
)
79 return css_to_vmpressure(cgroup_subsys_state(cg
, mem_cgroup_subsys_id
));
82 static struct vmpressure
*vmpressure_parent(struct vmpressure
*vmpr
)
84 struct cgroup
*cg
= vmpressure_to_css(vmpr
)->cgroup
;
85 struct mem_cgroup
*memcg
= mem_cgroup_from_cont(cg
);
87 memcg
= parent_mem_cgroup(memcg
);
90 return memcg_to_vmpressure(memcg
);
93 enum vmpressure_levels
{
97 VMPRESSURE_NUM_LEVELS
,
100 static const char * const vmpressure_str_levels
[] = {
101 [VMPRESSURE_LOW
] = "low",
102 [VMPRESSURE_MEDIUM
] = "medium",
103 [VMPRESSURE_CRITICAL
] = "critical",
106 static enum vmpressure_levels
vmpressure_level(unsigned long pressure
)
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
;
115 static enum vmpressure_levels
vmpressure_calc_level(unsigned long scanned
,
116 unsigned long reclaimed
)
118 unsigned long scale
= scanned
+ reclaimed
;
119 unsigned long pressure
= 0;
122 * reclaimed can be greater than scanned in cases
123 * like THP, where the scanned is 1 and reclaimed
126 if (reclaimed
>= scanned
)
129 * We calculate the ratio (in percents) of how many pages were
130 * scanned vs. reclaimed in a given time frame (window). Note that
131 * time is in VM reclaimer's "ticks", i.e. number of pages
132 * scanned. This makes it possible to set desired reaction time
133 * and serves as a ratelimit.
135 pressure
= scale
- (reclaimed
* scale
/ scanned
);
136 pressure
= pressure
* 100 / scale
;
139 pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__
, pressure
,
142 return vmpressure_level(pressure
);
145 struct vmpressure_event
{
146 struct eventfd_ctx
*efd
;
147 enum vmpressure_levels level
;
148 struct list_head node
;
151 static bool vmpressure_event(struct vmpressure
*vmpr
,
152 unsigned long scanned
, unsigned long reclaimed
)
154 struct vmpressure_event
*ev
;
155 enum vmpressure_levels level
;
156 bool signalled
= false;
158 level
= vmpressure_calc_level(scanned
, reclaimed
);
160 mutex_lock(&vmpr
->events_lock
);
162 list_for_each_entry(ev
, &vmpr
->events
, node
) {
163 if (level
>= ev
->level
) {
164 eventfd_signal(ev
->efd
, 1);
169 mutex_unlock(&vmpr
->events_lock
);
174 static void vmpressure_work_fn(struct work_struct
*work
)
176 struct vmpressure
*vmpr
= work_to_vmpressure(work
);
177 unsigned long scanned
;
178 unsigned long reclaimed
;
181 * Several contexts might be calling vmpressure(), so it is
182 * possible that the work was rescheduled again before the old
183 * work context cleared the counters. In that case we will run
184 * just after the old work returns, but then scanned might be zero
185 * here. No need for any locks here since we don't care if
186 * vmpr->reclaimed is in sync.
191 mutex_lock(&vmpr
->sr_lock
);
192 scanned
= vmpr
->scanned
;
193 reclaimed
= vmpr
->reclaimed
;
196 mutex_unlock(&vmpr
->sr_lock
);
199 if (vmpressure_event(vmpr
, scanned
, reclaimed
))
202 * If not handled, propagate the event upward into the
205 } while ((vmpr
= vmpressure_parent(vmpr
)));
209 * vmpressure() - Account memory pressure through scanned/reclaimed ratio
210 * @gfp: reclaimer's gfp mask
211 * @memcg: cgroup memory controller handle
212 * @scanned: number of pages scanned
213 * @reclaimed: number of pages reclaimed
215 * This function should be called from the vmscan reclaim path to account
216 * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
217 * pressure index is then further refined and averaged over time.
219 * This function does not return any value.
221 void vmpressure(gfp_t gfp
, struct mem_cgroup
*memcg
,
222 unsigned long scanned
, unsigned long reclaimed
)
224 struct vmpressure
*vmpr
= memcg_to_vmpressure(memcg
);
227 * Here we only want to account pressure that userland is able to
228 * help us with. For example, suppose that DMA zone is under
229 * pressure; if we notify userland about that kind of pressure,
230 * then it will be mostly a waste as it will trigger unnecessary
231 * freeing of memory by userland (since userland is more likely to
232 * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
233 * is why we include only movable, highmem and FS/IO pages.
234 * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
237 if (!(gfp
& (__GFP_HIGHMEM
| __GFP_MOVABLE
| __GFP_IO
| __GFP_FS
)))
241 * If we got here with no pages scanned, then that is an indicator
242 * that reclaimer was unable to find any shrinkable LRUs at the
243 * current scanning depth. But it does not mean that we should
244 * report the critical pressure, yet. If the scanning priority
245 * (scanning depth) goes too high (deep), we will be notified
246 * through vmpressure_prio(). But so far, keep calm.
251 mutex_lock(&vmpr
->sr_lock
);
252 vmpr
->scanned
+= scanned
;
253 vmpr
->reclaimed
+= reclaimed
;
254 scanned
= vmpr
->scanned
;
255 mutex_unlock(&vmpr
->sr_lock
);
257 if (scanned
< vmpressure_win
|| work_pending(&vmpr
->work
))
259 schedule_work(&vmpr
->work
);
263 * vmpressure_prio() - Account memory pressure through reclaimer priority level
264 * @gfp: reclaimer's gfp mask
265 * @memcg: cgroup memory controller handle
266 * @prio: reclaimer's priority
268 * This function should be called from the reclaim path every time when
269 * the vmscan's reclaiming priority (scanning depth) changes.
271 * This function does not return any value.
273 void vmpressure_prio(gfp_t gfp
, struct mem_cgroup
*memcg
, int prio
)
276 * We only use prio for accounting critical level. For more info
277 * see comment for vmpressure_level_critical_prio variable above.
279 if (prio
> vmpressure_level_critical_prio
)
283 * OK, the prio is below the threshold, updating vmpressure
284 * information before shrinker dives into long shrinking of long
285 * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
286 * to the vmpressure() basically means that we signal 'critical'
289 vmpressure(gfp
, memcg
, vmpressure_win
, 0);
293 * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
294 * @cg: cgroup that is interested in vmpressure notifications
295 * @cft: cgroup control files handle
296 * @eventfd: eventfd context to link notifications with
297 * @args: event arguments (used to set up a pressure level threshold)
299 * This function associates eventfd context with the vmpressure
300 * infrastructure, so that the notifications will be delivered to the
301 * @eventfd. The @args parameter is a string that denotes pressure level
302 * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
305 * This function should not be used directly, just pass it to (struct
306 * cftype).register_event, and then cgroup core will handle everything by
309 int vmpressure_register_event(struct cgroup
*cg
, struct cftype
*cft
,
310 struct eventfd_ctx
*eventfd
, const char *args
)
312 struct vmpressure
*vmpr
= cg_to_vmpressure(cg
);
313 struct vmpressure_event
*ev
;
316 for (level
= 0; level
< VMPRESSURE_NUM_LEVELS
; level
++) {
317 if (!strcmp(vmpressure_str_levels
[level
], args
))
321 if (level
>= VMPRESSURE_NUM_LEVELS
)
324 ev
= kzalloc(sizeof(*ev
), GFP_KERNEL
);
331 mutex_lock(&vmpr
->events_lock
);
332 list_add(&ev
->node
, &vmpr
->events
);
333 mutex_unlock(&vmpr
->events_lock
);
339 * vmpressure_unregister_event() - Unbind eventfd from vmpressure
341 * @cft: cgroup control files handle
342 * @eventfd: eventfd context that was used to link vmpressure with the @cg
344 * This function does internal manipulations to detach the @eventfd from
345 * the vmpressure notifications, and then frees internal resources
346 * associated with the @eventfd (but the @eventfd itself is not freed).
348 * This function should not be used directly, just pass it to (struct
349 * cftype).unregister_event, and then cgroup core will handle everything
352 void vmpressure_unregister_event(struct cgroup
*cg
, struct cftype
*cft
,
353 struct eventfd_ctx
*eventfd
)
355 struct vmpressure
*vmpr
= cg_to_vmpressure(cg
);
356 struct vmpressure_event
*ev
;
358 mutex_lock(&vmpr
->events_lock
);
359 list_for_each_entry(ev
, &vmpr
->events
, node
) {
360 if (ev
->efd
!= eventfd
)
366 mutex_unlock(&vmpr
->events_lock
);
370 * vmpressure_init() - Initialize vmpressure control structure
371 * @vmpr: Structure to be initialized
373 * This function should be called on every allocated vmpressure structure
376 void vmpressure_init(struct vmpressure
*vmpr
)
378 mutex_init(&vmpr
->sr_lock
);
379 mutex_init(&vmpr
->events_lock
);
380 INIT_LIST_HEAD(&vmpr
->events
);
381 INIT_WORK(&vmpr
->work
, vmpressure_work_fn
);