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