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                              unsigned long scanned, unsigned long reclaimed)
 149 {
 150         struct vmpressure_event *ev;
 151         enum vmpressure_levels level;
 152         bool signalled = false;
 153
 154         level = vmpressure_calc_level(scanned, reclaimed);
 155
 156         mutex_lock(&vmpr->events_lock);
 157
 158         list_for_each_entry(ev, &vmpr->events, node) {
 159                 if (level >= ev->level) {
 160                         eventfd_signal(ev->efd, 1);
 161                         signalled = true;
 162                 }
 163         }
 164
 165         mutex_unlock(&vmpr->events_lock);
 166
 167         return signalled;
 168 }
 169
 170 static void vmpressure_work_fn(struct work_struct *work)
 171 {
 172         struct vmpressure *vmpr = work_to_vmpressure(work);
 173         unsigned long scanned;
 174         unsigned long reclaimed;
 175
 176         spin_lock(&vmpr->sr_lock);
 177         /*
 178          * Several contexts might be calling vmpressure(), so it is
 179          * possible that the work was rescheduled again before the old
 180          * work context cleared the counters. In that case we will run
 181          * just after the old work returns, but then scanned might be zero
 182          * here. No need for any locks here since we don't care if
 183          * vmpr->reclaimed is in sync.
 184          */
 185         scanned = vmpr->scanned;
 186         if (!scanned) {
 187                 spin_unlock(&vmpr->sr_lock);
 188                 return;
 189         }
 190
 191         reclaimed = vmpr->reclaimed;
 192         vmpr->scanned = 0;
 193         vmpr->reclaimed = 0;
 194         spin_unlock(&vmpr->sr_lock);
 195
 196         do {
 197                 if (vmpressure_event(vmpr, scanned, reclaimed))
 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  * @scanned:    number of pages scanned
 211  * @reclaimed:  number of pages reclaimed
 212  *
 213  * This function should be called from the vmscan reclaim path to account
 214  * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
 215  * pressure index is then further refined and averaged over time.
 216  *
 217  * This function does not return any value.
 218  */
 219 void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
 220                 unsigned long scanned, unsigned long reclaimed)
 221 {
 222         struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 223
 224         /*
 225          * Here we only want to account pressure that userland is able to
 226          * help us with. For example, suppose that DMA zone is under
 227          * pressure; if we notify userland about that kind of pressure,
 228          * then it will be mostly a waste as it will trigger unnecessary
 229          * freeing of memory by userland (since userland is more likely to
 230          * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
 231          * is why we include only movable, highmem and FS/IO pages.
 232          * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
 233          * we account it too.
 234          */
 235         if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
 236                 return;
 237
 238         /*
 239          * If we got here with no pages scanned, then that is an indicator
 240          * that reclaimer was unable to find any shrinkable LRUs at the
 241          * current scanning depth. But it does not mean that we should
 242          * report the critical pressure, yet. If the scanning priority
 243          * (scanning depth) goes too high (deep), we will be notified
 244          * through vmpressure_prio(). But so far, keep calm.
 245          */
 246         if (!scanned)
 247                 return;
 248
 249         spin_lock(&vmpr->sr_lock);
 250         vmpr->scanned += scanned;
 251         vmpr->reclaimed += reclaimed;
 252         scanned = vmpr->scanned;
 253         spin_unlock(&vmpr->sr_lock);
 254
 255         if (scanned < vmpressure_win)
 256                 return;
 257         schedule_work(&vmpr->work);
 258 }
 259
 260 /**
 261  * vmpressure_prio() - Account memory pressure through reclaimer priority level
 262  * @gfp:        reclaimer's gfp mask
 263  * @memcg:      cgroup memory controller handle
 264  * @prio:       reclaimer's priority
 265  *
 266  * This function should be called from the reclaim path every time when
 267  * the vmscan's reclaiming priority (scanning depth) changes.
 268  *
 269  * This function does not return any value.
 270  */
 271 void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
 272 {
 273         /*
 274          * We only use prio for accounting critical level. For more info
 275          * see comment for vmpressure_level_critical_prio variable above.
 276          */
 277         if (prio > vmpressure_level_critical_prio)
 278                 return;
 279
 280         /*
 281          * OK, the prio is below the threshold, updating vmpressure
 282          * information before shrinker dives into long shrinking of long
 283          * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
 284          * to the vmpressure() basically means that we signal 'critical'
 285          * level.
 286          */
 287         vmpressure(gfp, memcg, vmpressure_win, 0);
 288 }
 289
 290 /**
 291  * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
 292  * @memcg:      memcg that is interested in vmpressure notifications
 293  * @eventfd:    eventfd context to link notifications with
 294  * @args:       event arguments (used to set up a pressure level threshold)
 295  *
 296  * This function associates eventfd context with the vmpressure
 297  * infrastructure, so that the notifications will be delivered to the
 298  * @eventfd. The @args parameter is a string that denotes pressure level
 299  * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
 300  * "critical").
 301  *
 302  * To be used as memcg event method.
 303  */
 304 int vmpressure_register_event(struct mem_cgroup *memcg,
 305                               struct eventfd_ctx *eventfd, const char *args)
 306 {
 307         struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 308         struct vmpressure_event *ev;
 309         int level;
 310
 311         for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
 312                 if (!strcmp(vmpressure_str_levels[level], args))
 313                         break;
 314         }
 315
 316         if (level >= VMPRESSURE_NUM_LEVELS)
 317                 return -EINVAL;
 318
 319         ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 320         if (!ev)
 321                 return -ENOMEM;
 322
 323         ev->efd = eventfd;
 324         ev->level = level;
 325
 326         mutex_lock(&vmpr->events_lock);
 327         list_add(&ev->node, &vmpr->events);
 328         mutex_unlock(&vmpr->events_lock);
 329
 330         return 0;
 331 }
 332
 333 /**
 334  * vmpressure_unregister_event() - Unbind eventfd from vmpressure
 335  * @memcg:      memcg handle
 336  * @eventfd:    eventfd context that was used to link vmpressure with the @cg
 337  *
 338  * This function does internal manipulations to detach the @eventfd from
 339  * the vmpressure notifications, and then frees internal resources
 340  * associated with the @eventfd (but the @eventfd itself is not freed).
 341  *
 342  * To be used as memcg event method.
 343  */
 344 void vmpressure_unregister_event(struct mem_cgroup *memcg,
 345                                  struct eventfd_ctx *eventfd)
 346 {
 347         struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 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  */
 368 void vmpressure_init(struct vmpressure *vmpr)
 369 {
 370         spin_lock_init(&vmpr->sr_lock);
 371         mutex_init(&vmpr->events_lock);
 372         INIT_LIST_HEAD(&vmpr->events);
 373         INIT_WORK(&vmpr->work, vmpressure_work_fn);
 374 }
 375
 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  */
 383 void 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 }