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 enum vmpressure_modes {
  97         VMPRESSURE_NO_PASSTHROUGH = 0,
  98         VMPRESSURE_HIERARCHY,
  99         VMPRESSURE_LOCAL,
 100         VMPRESSURE_NUM_MODES,
 101 };
 102
 103 static const char * const vmpressure_str_levels[] = {
 104         [VMPRESSURE_LOW] = "low",
 105         [VMPRESSURE_MEDIUM] = "medium",
 106         [VMPRESSURE_CRITICAL] = "critical",
 107 };
 108
 109 static const char * const vmpressure_str_modes[] = {
 110         [VMPRESSURE_NO_PASSTHROUGH] = "default",
 111         [VMPRESSURE_HIERARCHY] = "hierarchy",
 112         [VMPRESSURE_LOCAL] = "local",
 113 };
 114
 115 static enum vmpressure_levels vmpressure_level(unsigned long pressure)
 116 {
 117         if (pressure >= vmpressure_level_critical)
 118                 return VMPRESSURE_CRITICAL;
 119         else if (pressure >= vmpressure_level_med)
 120                 return VMPRESSURE_MEDIUM;
 121         return VMPRESSURE_LOW;
 122 }
 123
 124 static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
 125                                                     unsigned long reclaimed)
 126 {
 127         unsigned long scale = scanned + reclaimed;
 128         unsigned long pressure = 0;
 129
 130         /*
 131          * reclaimed can be greater than scanned for things such as reclaimed
 132          * slab pages. shrink_node() just adds reclaimed pages without a
 133          * related increment to scanned pages.
 134          */
 135         if (reclaimed >= scanned)
 136                 goto out;
 137         /*
 138          * We calculate the ratio (in percents) of how many pages were
 139          * scanned vs. reclaimed in a given time frame (window). Note that
 140          * time is in VM reclaimer's "ticks", i.e. number of pages
 141          * scanned. This makes it possible to set desired reaction time
 142          * and serves as a ratelimit.
 143          */
 144         pressure = scale - (reclaimed * scale / scanned);
 145         pressure = pressure * 100 / scale;
 146
 147 out:
 148         pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
 149                  scanned, reclaimed);
 150
 151         return vmpressure_level(pressure);
 152 }
 153
 154 struct vmpressure_event {
 155         struct eventfd_ctx *efd;
 156         enum vmpressure_levels level;
 157         enum vmpressure_modes mode;
 158         struct list_head node;
 159 };
 160
 161 static bool vmpressure_event(struct vmpressure *vmpr,
 162                              const enum vmpressure_levels level,
 163                              bool ancestor, bool signalled)
 164 {
 165         struct vmpressure_event *ev;
 166         bool ret = false;
 167
 168         mutex_lock(&vmpr->events_lock);
 169         list_for_each_entry(ev, &vmpr->events, node) {
 170                 if (ancestor && ev->mode == VMPRESSURE_LOCAL)
 171                         continue;
 172                 if (signalled && ev->mode == VMPRESSURE_NO_PASSTHROUGH)
 173                         continue;
 174                 if (level < ev->level)
 175                         continue;
 176                 eventfd_signal(ev->efd, 1);
 177                 ret = true;
 178         }
 179         mutex_unlock(&vmpr->events_lock);
 180
 181         return ret;
 182 }
 183
 184 static void vmpressure_work_fn(struct work_struct *work)
 185 {
 186         struct vmpressure *vmpr = work_to_vmpressure(work);
 187         unsigned long scanned;
 188         unsigned long reclaimed;
 189         enum vmpressure_levels level;
 190         bool ancestor = false;
 191         bool signalled = false;
 192
 193         spin_lock(&vmpr->sr_lock);
 194         /*
 195          * Several contexts might be calling vmpressure(), so it is
 196          * possible that the work was rescheduled again before the old
 197          * work context cleared the counters. In that case we will run
 198          * just after the old work returns, but then scanned might be zero
 199          * here. No need for any locks here since we don't care if
 200          * vmpr->reclaimed is in sync.
 201          */
 202         scanned = vmpr->tree_scanned;
 203         if (!scanned) {
 204                 spin_unlock(&vmpr->sr_lock);
 205                 return;
 206         }
 207
 208         reclaimed = vmpr->tree_reclaimed;
 209         vmpr->tree_scanned = 0;
 210         vmpr->tree_reclaimed = 0;
 211         spin_unlock(&vmpr->sr_lock);
 212
 213         level = vmpressure_calc_level(scanned, reclaimed);
 214
 215         do {
 216                 if (vmpressure_event(vmpr, level, ancestor, signalled))
 217                         signalled = true;
 218                 ancestor = true;
 219         } while ((vmpr = vmpressure_parent(vmpr)));
 220 }
 221
 222 /**
 223  * vmpressure() - Account memory pressure through scanned/reclaimed ratio
 224  * @gfp:        reclaimer's gfp mask
 225  * @memcg:      cgroup memory controller handle
 226  * @tree:       legacy subtree mode
 227  * @scanned:    number of pages scanned
 228  * @reclaimed:  number of pages reclaimed
 229  *
 230  * This function should be called from the vmscan reclaim path to account
 231  * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
 232  * pressure index is then further refined and averaged over time.
 233  *
 234  * If @tree is set, vmpressure is in traditional userspace reporting
 235  * mode: @memcg is considered the pressure root and userspace is
 236  * notified of the entire subtree's reclaim efficiency.
 237  *
 238  * If @tree is not set, reclaim efficiency is recorded for @memcg, and
 239  * only in-kernel users are notified.
 240  *
 241  * This function does not return any value.
 242  */
 243 void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
 244                 unsigned long scanned, unsigned long reclaimed)
 245 {
 246         struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 247
 248         /*
 249          * Here we only want to account pressure that userland is able to
 250          * help us with. For example, suppose that DMA zone is under
 251          * pressure; if we notify userland about that kind of pressure,
 252          * then it will be mostly a waste as it will trigger unnecessary
 253          * freeing of memory by userland (since userland is more likely to
 254          * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
 255          * is why we include only movable, highmem and FS/IO pages.
 256          * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
 257          * we account it too.
 258          */
 259         if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
 260                 return;
 261
 262         /*
 263          * If we got here with no pages scanned, then that is an indicator
 264          * that reclaimer was unable to find any shrinkable LRUs at the
 265          * current scanning depth. But it does not mean that we should
 266          * report the critical pressure, yet. If the scanning priority
 267          * (scanning depth) goes too high (deep), we will be notified
 268          * through vmpressure_prio(). But so far, keep calm.
 269          */
 270         if (!scanned)
 271                 return;
 272
 273         if (tree) {
 274                 spin_lock(&vmpr->sr_lock);
 275                 scanned = vmpr->tree_scanned += scanned;
 276                 vmpr->tree_reclaimed += reclaimed;
 277                 spin_unlock(&vmpr->sr_lock);
 278
 279                 if (scanned < vmpressure_win)
 280                         return;
 281                 schedule_work(&vmpr->work);
 282         } else {
 283                 enum vmpressure_levels level;
 284
 285                 /* For now, no users for root-level efficiency */
 286                 if (!memcg || memcg == root_mem_cgroup)
 287                         return;
 288
 289                 spin_lock(&vmpr->sr_lock);
 290                 scanned = vmpr->scanned += scanned;
 291                 reclaimed = vmpr->reclaimed += reclaimed;
 292                 if (scanned < vmpressure_win) {
 293                         spin_unlock(&vmpr->sr_lock);
 294                         return;
 295                 }
 296                 vmpr->scanned = vmpr->reclaimed = 0;
 297                 spin_unlock(&vmpr->sr_lock);
 298
 299                 level = vmpressure_calc_level(scanned, reclaimed);
 300
 301                 if (level > VMPRESSURE_LOW) {
 302                         /*
 303                          * Let the socket buffer allocator know that
 304                          * we are having trouble reclaiming LRU pages.
 305                          *
 306                          * For hysteresis keep the pressure state
 307                          * asserted for a second in which subsequent
 308                          * pressure events can occur.
 309                          */
 310                         memcg->socket_pressure = jiffies + HZ;
 311                 }
 312         }
 313 }
 314
 315 /**
 316  * vmpressure_prio() - Account memory pressure through reclaimer priority level
 317  * @gfp:        reclaimer's gfp mask
 318  * @memcg:      cgroup memory controller handle
 319  * @prio:       reclaimer's priority
 320  *
 321  * This function should be called from the reclaim path every time when
 322  * the vmscan's reclaiming priority (scanning depth) changes.
 323  *
 324  * This function does not return any value.
 325  */
 326 void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
 327 {
 328         /*
 329          * We only use prio for accounting critical level. For more info
 330          * see comment for vmpressure_level_critical_prio variable above.
 331          */
 332         if (prio > vmpressure_level_critical_prio)
 333                 return;
 334
 335         /*
 336          * OK, the prio is below the threshold, updating vmpressure
 337          * information before shrinker dives into long shrinking of long
 338          * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
 339          * to the vmpressure() basically means that we signal 'critical'
 340          * level.
 341          */
 342         vmpressure(gfp, memcg, true, vmpressure_win, 0);
 343 }
 344
 345 #define MAX_VMPRESSURE_ARGS_LEN (strlen("critical") + strlen("hierarchy") + 2)
 346
 347 /**
 348  * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
 349  * @memcg:      memcg that is interested in vmpressure notifications
 350  * @eventfd:    eventfd context to link notifications with
 351  * @args:       event arguments (pressure level threshold, optional mode)
 352  *
 353  * This function associates eventfd context with the vmpressure
 354  * infrastructure, so that the notifications will be delivered to the
 355  * @eventfd. The @args parameter is a comma-delimited string that denotes a
 356  * pressure level threshold (one of vmpressure_str_levels, i.e. "low", "medium",
 357  * or "critical") and an optional mode (one of vmpressure_str_modes, i.e.
 358  * "hierarchy" or "local").
 359  *
 360  * To be used as memcg event method.
 361  */
 362 int vmpressure_register_event(struct mem_cgroup *memcg,
 363                               struct eventfd_ctx *eventfd, const char *args)
 364 {
 365         struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 366         struct vmpressure_event *ev;
 367         enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH;
 368         enum vmpressure_levels level = -1;
 369         char *spec, *spec_orig;
 370         char *token;
 371         int ret = 0;
 372
 373         spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
 374         if (!spec) {
 375                 ret = -ENOMEM;
 376                 goto out;
 377         }
 378
 379         /* Find required level */
 380         token = strsep(&spec, ",");
 381         level = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token);
 382         if (level < 0) {
 383                 ret = level;
 384                 goto out;
 385         }
 386
 387         /* Find optional mode */
 388         token = strsep(&spec, ",");
 389         if (token) {
 390                 mode = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token);
 391                 if (mode < 0) {
 392                         ret = mode;
 393                         goto out;
 394                 }
 395         }
 396
 397         ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 398         if (!ev) {
 399                 ret = -ENOMEM;
 400                 goto out;
 401         }
 402
 403         ev->efd = eventfd;
 404         ev->level = level;
 405         ev->mode = mode;
 406
 407         mutex_lock(&vmpr->events_lock);
 408         list_add(&ev->node, &vmpr->events);
 409         mutex_unlock(&vmpr->events_lock);
 410 out:
 411         kfree(spec_orig);
 412         return ret;
 413 }
 414
 415 /**
 416  * vmpressure_unregister_event() - Unbind eventfd from vmpressure
 417  * @memcg:      memcg handle
 418  * @eventfd:    eventfd context that was used to link vmpressure with the @cg
 419  *
 420  * This function does internal manipulations to detach the @eventfd from
 421  * the vmpressure notifications, and then frees internal resources
 422  * associated with the @eventfd (but the @eventfd itself is not freed).
 423  *
 424  * To be used as memcg event method.
 425  */
 426 void vmpressure_unregister_event(struct mem_cgroup *memcg,
 427                                  struct eventfd_ctx *eventfd)
 428 {
 429         struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 430         struct vmpressure_event *ev;
 431
 432         mutex_lock(&vmpr->events_lock);
 433         list_for_each_entry(ev, &vmpr->events, node) {
 434                 if (ev->efd != eventfd)
 435                         continue;
 436                 list_del(&ev->node);
 437                 kfree(ev);
 438                 break;
 439         }
 440         mutex_unlock(&vmpr->events_lock);
 441 }
 442
 443 /**
 444  * vmpressure_init() - Initialize vmpressure control structure
 445  * @vmpr:       Structure to be initialized
 446  *
 447  * This function should be called on every allocated vmpressure structure
 448  * before any usage.
 449  */
 450 void vmpressure_init(struct vmpressure *vmpr)
 451 {
 452         spin_lock_init(&vmpr->sr_lock);
 453         mutex_init(&vmpr->events_lock);
 454         INIT_LIST_HEAD(&vmpr->events);
 455         INIT_WORK(&vmpr->work, vmpressure_work_fn);
 456 }
 457
 458 /**
 459  * vmpressure_cleanup() - shuts down vmpressure control structure
 460  * @vmpr:       Structure to be cleaned up
 461  *
 462  * This function should be called before the structure in which it is
 463  * embedded is cleaned up.
 464  */
 465 void vmpressure_cleanup(struct vmpressure *vmpr)
 466 {
 467         /*
 468          * Make sure there is no pending work before eventfd infrastructure
 469          * goes away.
 470          */
 471         flush_work(&vmpr->work);
 472 }