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