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 enum vmpressure_levels level) 149 { 150 struct vmpressure_event *ev; 151 bool signalled = false; 152 153 mutex_lock(&vmpr->events_lock); 154 155 list_for_each_entry(ev, &vmpr->events, node) { 156 if (level >= ev->level) { 157 eventfd_signal(ev->efd, 1); 158 signalled = true; 159 } 160 } 161 162 mutex_unlock(&vmpr->events_lock); 163 164 return signalled; 165 } 166 167 static void vmpressure_work_fn(struct work_struct *work) 168 { 169 struct vmpressure *vmpr = work_to_vmpressure(work); 170 unsigned long scanned; 171 unsigned long reclaimed; 172 enum vmpressure_levels level; 173 174 spin_lock(&vmpr->sr_lock); 175 /* 176 * Several contexts might be calling vmpressure(), so it is 177 * possible that the work was rescheduled again before the old 178 * work context cleared the counters. In that case we will run 179 * just after the old work returns, but then scanned might be zero 180 * here. No need for any locks here since we don't care if 181 * vmpr->reclaimed is in sync. 182 */ 183 scanned = vmpr->tree_scanned; 184 if (!scanned) { 185 spin_unlock(&vmpr->sr_lock); 186 return; 187 } 188 189 reclaimed = vmpr->tree_reclaimed; 190 vmpr->tree_scanned = 0; 191 vmpr->tree_reclaimed = 0; 192 spin_unlock(&vmpr->sr_lock); 193 194 level = vmpressure_calc_level(scanned, reclaimed); 195 196 do { 197 if (vmpressure_event(vmpr, level)) 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 * @tree: legacy subtree mode 211 * @scanned: number of pages scanned 212 * @reclaimed: number of pages reclaimed 213 * 214 * This function should be called from the vmscan reclaim path to account 215 * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw 216 * pressure index is then further refined and averaged over time. 217 * 218 * If @tree is set, vmpressure is in traditional userspace reporting 219 * mode: @memcg is considered the pressure root and userspace is 220 * notified of the entire subtree's reclaim efficiency. 221 * 222 * If @tree is not set, reclaim efficiency is recorded for @memcg, and 223 * only in-kernel users are notified. 224 * 225 * This function does not return any value. 226 */ 227 void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree, 228 unsigned long scanned, unsigned long reclaimed) 229 { 230 struct vmpressure *vmpr = memcg_to_vmpressure(memcg); 231 232 /* 233 * Here we only want to account pressure that userland is able to 234 * help us with. For example, suppose that DMA zone is under 235 * pressure; if we notify userland about that kind of pressure, 236 * then it will be mostly a waste as it will trigger unnecessary 237 * freeing of memory by userland (since userland is more likely to 238 * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That 239 * is why we include only movable, highmem and FS/IO pages. 240 * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so 241 * we account it too. 242 */ 243 if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS))) 244 return; 245 246 /* 247 * If we got here with no pages scanned, then that is an indicator 248 * that reclaimer was unable to find any shrinkable LRUs at the 249 * current scanning depth. But it does not mean that we should 250 * report the critical pressure, yet. If the scanning priority 251 * (scanning depth) goes too high (deep), we will be notified 252 * through vmpressure_prio(). But so far, keep calm. 253 */ 254 if (!scanned) 255 return; 256 257 if (tree) { 258 spin_lock(&vmpr->sr_lock); 259 scanned = vmpr->tree_scanned += scanned; 260 vmpr->tree_reclaimed += reclaimed; 261 spin_unlock(&vmpr->sr_lock); 262 263 if (scanned < vmpressure_win) 264 return; 265 schedule_work(&vmpr->work); 266 } else { 267 enum vmpressure_levels level; 268 269 /* For now, no users for root-level efficiency */ 270 if (!memcg || memcg == root_mem_cgroup) 271 return; 272 273 spin_lock(&vmpr->sr_lock); 274 scanned = vmpr->scanned += scanned; 275 reclaimed = vmpr->reclaimed += reclaimed; 276 if (scanned < vmpressure_win) { 277 spin_unlock(&vmpr->sr_lock); 278 return; 279 } 280 vmpr->scanned = vmpr->reclaimed = 0; 281 spin_unlock(&vmpr->sr_lock); 282 283 level = vmpressure_calc_level(scanned, reclaimed); 284 285 if (level > VMPRESSURE_LOW) { 286 /* 287 * Let the socket buffer allocator know that 288 * we are having trouble reclaiming LRU pages. 289 * 290 * For hysteresis keep the pressure state 291 * asserted for a second in which subsequent 292 * pressure events can occur. 293 */ 294 memcg->socket_pressure = jiffies + HZ; 295 } 296 } 297 } 298 299 /** 300 * vmpressure_prio() - Account memory pressure through reclaimer priority level 301 * @gfp: reclaimer's gfp mask 302 * @memcg: cgroup memory controller handle 303 * @prio: reclaimer's priority 304 * 305 * This function should be called from the reclaim path every time when 306 * the vmscan's reclaiming priority (scanning depth) changes. 307 * 308 * This function does not return any value. 309 */ 310 void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio) 311 { 312 /* 313 * We only use prio for accounting critical level. For more info 314 * see comment for vmpressure_level_critical_prio variable above. 315 */ 316 if (prio > vmpressure_level_critical_prio) 317 return; 318 319 /* 320 * OK, the prio is below the threshold, updating vmpressure 321 * information before shrinker dives into long shrinking of long 322 * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0 323 * to the vmpressure() basically means that we signal 'critical' 324 * level. 325 */ 326 vmpressure(gfp, memcg, true, vmpressure_win, 0); 327 } 328 329 /** 330 * vmpressure_register_event() - Bind vmpressure notifications to an eventfd 331 * @memcg: memcg that is interested in vmpressure notifications 332 * @eventfd: eventfd context to link notifications with 333 * @args: event arguments (used to set up a pressure level threshold) 334 * 335 * This function associates eventfd context with the vmpressure 336 * infrastructure, so that the notifications will be delivered to the 337 * @eventfd. The @args parameter is a string that denotes pressure level 338 * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or 339 * "critical"). 340 * 341 * To be used as memcg event method. 342 */ 343 int vmpressure_register_event(struct mem_cgroup *memcg, 344 struct eventfd_ctx *eventfd, const char *args) 345 { 346 struct vmpressure *vmpr = memcg_to_vmpressure(memcg); 347 struct vmpressure_event *ev; 348 int level; 349 350 for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) { 351 if (!strcmp(vmpressure_str_levels[level], args)) 352 break; 353 } 354 355 if (level >= VMPRESSURE_NUM_LEVELS) 356 return -EINVAL; 357 358 ev = kzalloc(sizeof(*ev), GFP_KERNEL); 359 if (!ev) 360 return -ENOMEM; 361 362 ev->efd = eventfd; 363 ev->level = level; 364 365 mutex_lock(&vmpr->events_lock); 366 list_add(&ev->node, &vmpr->events); 367 mutex_unlock(&vmpr->events_lock); 368 369 return 0; 370 } 371 372 /** 373 * vmpressure_unregister_event() - Unbind eventfd from vmpressure 374 * @memcg: memcg handle 375 * @eventfd: eventfd context that was used to link vmpressure with the @cg 376 * 377 * This function does internal manipulations to detach the @eventfd from 378 * the vmpressure notifications, and then frees internal resources 379 * associated with the @eventfd (but the @eventfd itself is not freed). 380 * 381 * To be used as memcg event method. 382 */ 383 void vmpressure_unregister_event(struct mem_cgroup *memcg, 384 struct eventfd_ctx *eventfd) 385 { 386 struct vmpressure *vmpr = memcg_to_vmpressure(memcg); 387 struct vmpressure_event *ev; 388 389 mutex_lock(&vmpr->events_lock); 390 list_for_each_entry(ev, &vmpr->events, node) { 391 if (ev->efd != eventfd) 392 continue; 393 list_del(&ev->node); 394 kfree(ev); 395 break; 396 } 397 mutex_unlock(&vmpr->events_lock); 398 } 399 400 /** 401 * vmpressure_init() - Initialize vmpressure control structure 402 * @vmpr: Structure to be initialized 403 * 404 * This function should be called on every allocated vmpressure structure 405 * before any usage. 406 */ 407 void vmpressure_init(struct vmpressure *vmpr) 408 { 409 spin_lock_init(&vmpr->sr_lock); 410 mutex_init(&vmpr->events_lock); 411 INIT_LIST_HEAD(&vmpr->events); 412 INIT_WORK(&vmpr->work, vmpressure_work_fn); 413 } 414 415 /** 416 * vmpressure_cleanup() - shuts down vmpressure control structure 417 * @vmpr: Structure to be cleaned up 418 * 419 * This function should be called before the structure in which it is 420 * embedded is cleaned up. 421 */ 422 void vmpressure_cleanup(struct vmpressure *vmpr) 423 { 424 /* 425 * Make sure there is no pending work before eventfd infrastructure 426 * goes away. 427 */ 428 flush_work(&vmpr->work); 429 } 430