Tim Chen | 67afa38 | 2017-02-22 15:45:39 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Manage cache of swap slots to be used for and returned from |
| 3 | * swap. |
| 4 | * |
| 5 | * Copyright(c) 2016 Intel Corporation. |
| 6 | * |
| 7 | * Author: Tim Chen <tim.c.chen@linux.intel.com> |
| 8 | * |
| 9 | * We allocate the swap slots from the global pool and put |
| 10 | * it into local per cpu caches. This has the advantage |
| 11 | * of no needing to acquire the swap_info lock every time |
| 12 | * we need a new slot. |
| 13 | * |
| 14 | * There is also opportunity to simply return the slot |
| 15 | * to local caches without needing to acquire swap_info |
| 16 | * lock. We do not reuse the returned slots directly but |
| 17 | * move them back to the global pool in a batch. This |
| 18 | * allows the slots to coaellesce and reduce fragmentation. |
| 19 | * |
| 20 | * The swap entry allocated is marked with SWAP_HAS_CACHE |
| 21 | * flag in map_count that prevents it from being allocated |
| 22 | * again from the global pool. |
| 23 | * |
| 24 | * The swap slots cache is protected by a mutex instead of |
| 25 | * a spin lock as when we search for slots with scan_swap_map, |
| 26 | * we can possibly sleep. |
| 27 | */ |
| 28 | |
| 29 | #include <linux/swap_slots.h> |
| 30 | #include <linux/cpu.h> |
| 31 | #include <linux/cpumask.h> |
| 32 | #include <linux/vmalloc.h> |
| 33 | #include <linux/mutex.h> |
| 34 | |
| 35 | #ifdef CONFIG_SWAP |
| 36 | |
| 37 | static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots); |
| 38 | static bool swap_slot_cache_active; |
Huang Ying | ba81f83 | 2017-02-22 15:45:46 -0800 | [diff] [blame] | 39 | bool swap_slot_cache_enabled; |
Tim Chen | 67afa38 | 2017-02-22 15:45:39 -0800 | [diff] [blame] | 40 | static bool swap_slot_cache_initialized; |
| 41 | DEFINE_MUTEX(swap_slots_cache_mutex); |
| 42 | /* Serialize swap slots cache enable/disable operations */ |
| 43 | DEFINE_MUTEX(swap_slots_cache_enable_mutex); |
| 44 | |
| 45 | static void __drain_swap_slots_cache(unsigned int type); |
| 46 | static void deactivate_swap_slots_cache(void); |
| 47 | static void reactivate_swap_slots_cache(void); |
| 48 | |
| 49 | #define use_swap_slot_cache (swap_slot_cache_active && \ |
| 50 | swap_slot_cache_enabled && swap_slot_cache_initialized) |
| 51 | #define SLOTS_CACHE 0x1 |
| 52 | #define SLOTS_CACHE_RET 0x2 |
| 53 | |
| 54 | static void deactivate_swap_slots_cache(void) |
| 55 | { |
| 56 | mutex_lock(&swap_slots_cache_mutex); |
| 57 | swap_slot_cache_active = false; |
| 58 | __drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET); |
| 59 | mutex_unlock(&swap_slots_cache_mutex); |
| 60 | } |
| 61 | |
| 62 | static void reactivate_swap_slots_cache(void) |
| 63 | { |
| 64 | mutex_lock(&swap_slots_cache_mutex); |
| 65 | swap_slot_cache_active = true; |
| 66 | mutex_unlock(&swap_slots_cache_mutex); |
| 67 | } |
| 68 | |
| 69 | /* Must not be called with cpu hot plug lock */ |
| 70 | void disable_swap_slots_cache_lock(void) |
| 71 | { |
| 72 | mutex_lock(&swap_slots_cache_enable_mutex); |
| 73 | swap_slot_cache_enabled = false; |
| 74 | if (swap_slot_cache_initialized) { |
| 75 | /* serialize with cpu hotplug operations */ |
| 76 | get_online_cpus(); |
| 77 | __drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET); |
| 78 | put_online_cpus(); |
| 79 | } |
| 80 | } |
| 81 | |
| 82 | static void __reenable_swap_slots_cache(void) |
| 83 | { |
| 84 | swap_slot_cache_enabled = has_usable_swap(); |
| 85 | } |
| 86 | |
| 87 | void reenable_swap_slots_cache_unlock(void) |
| 88 | { |
| 89 | __reenable_swap_slots_cache(); |
| 90 | mutex_unlock(&swap_slots_cache_enable_mutex); |
| 91 | } |
| 92 | |
| 93 | static bool check_cache_active(void) |
| 94 | { |
| 95 | long pages; |
| 96 | |
| 97 | if (!swap_slot_cache_enabled || !swap_slot_cache_initialized) |
| 98 | return false; |
| 99 | |
| 100 | pages = get_nr_swap_pages(); |
| 101 | if (!swap_slot_cache_active) { |
| 102 | if (pages > num_online_cpus() * |
| 103 | THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE) |
| 104 | reactivate_swap_slots_cache(); |
| 105 | goto out; |
| 106 | } |
| 107 | |
| 108 | /* if global pool of slot caches too low, deactivate cache */ |
| 109 | if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE) |
| 110 | deactivate_swap_slots_cache(); |
| 111 | out: |
| 112 | return swap_slot_cache_active; |
| 113 | } |
| 114 | |
| 115 | static int alloc_swap_slot_cache(unsigned int cpu) |
| 116 | { |
| 117 | struct swap_slots_cache *cache; |
| 118 | swp_entry_t *slots, *slots_ret; |
| 119 | |
| 120 | /* |
| 121 | * Do allocation outside swap_slots_cache_mutex |
| 122 | * as vzalloc could trigger reclaim and get_swap_page, |
| 123 | * which can lock swap_slots_cache_mutex. |
| 124 | */ |
| 125 | slots = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE); |
| 126 | if (!slots) |
| 127 | return -ENOMEM; |
| 128 | |
| 129 | slots_ret = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE); |
| 130 | if (!slots_ret) { |
| 131 | vfree(slots); |
| 132 | return -ENOMEM; |
| 133 | } |
| 134 | |
| 135 | mutex_lock(&swap_slots_cache_mutex); |
| 136 | cache = &per_cpu(swp_slots, cpu); |
| 137 | if (cache->slots || cache->slots_ret) |
| 138 | /* cache already allocated */ |
| 139 | goto out; |
| 140 | if (!cache->lock_initialized) { |
| 141 | mutex_init(&cache->alloc_lock); |
| 142 | spin_lock_init(&cache->free_lock); |
| 143 | cache->lock_initialized = true; |
| 144 | } |
| 145 | cache->nr = 0; |
| 146 | cache->cur = 0; |
| 147 | cache->n_ret = 0; |
| 148 | cache->slots = slots; |
| 149 | slots = NULL; |
| 150 | cache->slots_ret = slots_ret; |
| 151 | slots_ret = NULL; |
| 152 | out: |
| 153 | mutex_unlock(&swap_slots_cache_mutex); |
| 154 | if (slots) |
| 155 | vfree(slots); |
| 156 | if (slots_ret) |
| 157 | vfree(slots_ret); |
| 158 | return 0; |
| 159 | } |
| 160 | |
| 161 | static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type, |
| 162 | bool free_slots) |
| 163 | { |
| 164 | struct swap_slots_cache *cache; |
| 165 | swp_entry_t *slots = NULL; |
| 166 | |
| 167 | cache = &per_cpu(swp_slots, cpu); |
| 168 | if ((type & SLOTS_CACHE) && cache->slots) { |
| 169 | mutex_lock(&cache->alloc_lock); |
| 170 | swapcache_free_entries(cache->slots + cache->cur, cache->nr); |
| 171 | cache->cur = 0; |
| 172 | cache->nr = 0; |
| 173 | if (free_slots && cache->slots) { |
| 174 | vfree(cache->slots); |
| 175 | cache->slots = NULL; |
| 176 | } |
| 177 | mutex_unlock(&cache->alloc_lock); |
| 178 | } |
| 179 | if ((type & SLOTS_CACHE_RET) && cache->slots_ret) { |
| 180 | spin_lock_irq(&cache->free_lock); |
| 181 | swapcache_free_entries(cache->slots_ret, cache->n_ret); |
| 182 | cache->n_ret = 0; |
| 183 | if (free_slots && cache->slots_ret) { |
| 184 | slots = cache->slots_ret; |
| 185 | cache->slots_ret = NULL; |
| 186 | } |
| 187 | spin_unlock_irq(&cache->free_lock); |
| 188 | if (slots) |
| 189 | vfree(slots); |
| 190 | } |
| 191 | } |
| 192 | |
| 193 | static void __drain_swap_slots_cache(unsigned int type) |
| 194 | { |
| 195 | unsigned int cpu; |
| 196 | |
| 197 | /* |
| 198 | * This function is called during |
| 199 | * 1) swapoff, when we have to make sure no |
| 200 | * left over slots are in cache when we remove |
| 201 | * a swap device; |
| 202 | * 2) disabling of swap slot cache, when we run low |
| 203 | * on swap slots when allocating memory and need |
| 204 | * to return swap slots to global pool. |
| 205 | * |
| 206 | * We cannot acquire cpu hot plug lock here as |
| 207 | * this function can be invoked in the cpu |
| 208 | * hot plug path: |
| 209 | * cpu_up -> lock cpu_hotplug -> cpu hotplug state callback |
| 210 | * -> memory allocation -> direct reclaim -> get_swap_page |
| 211 | * -> drain_swap_slots_cache |
| 212 | * |
| 213 | * Hence the loop over current online cpu below could miss cpu that |
| 214 | * is being brought online but not yet marked as online. |
| 215 | * That is okay as we do not schedule and run anything on a |
| 216 | * cpu before it has been marked online. Hence, we will not |
| 217 | * fill any swap slots in slots cache of such cpu. |
| 218 | * There are no slots on such cpu that need to be drained. |
| 219 | */ |
| 220 | for_each_online_cpu(cpu) |
| 221 | drain_slots_cache_cpu(cpu, type, false); |
| 222 | } |
| 223 | |
| 224 | static int free_slot_cache(unsigned int cpu) |
| 225 | { |
| 226 | mutex_lock(&swap_slots_cache_mutex); |
| 227 | drain_slots_cache_cpu(cpu, SLOTS_CACHE | SLOTS_CACHE_RET, true); |
| 228 | mutex_unlock(&swap_slots_cache_mutex); |
| 229 | return 0; |
| 230 | } |
| 231 | |
| 232 | int enable_swap_slots_cache(void) |
| 233 | { |
| 234 | int ret = 0; |
| 235 | |
| 236 | mutex_lock(&swap_slots_cache_enable_mutex); |
| 237 | if (swap_slot_cache_initialized) { |
| 238 | __reenable_swap_slots_cache(); |
| 239 | goto out_unlock; |
| 240 | } |
| 241 | |
| 242 | ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache", |
| 243 | alloc_swap_slot_cache, free_slot_cache); |
| 244 | if (ret < 0) |
| 245 | goto out_unlock; |
| 246 | swap_slot_cache_initialized = true; |
| 247 | __reenable_swap_slots_cache(); |
| 248 | out_unlock: |
| 249 | mutex_unlock(&swap_slots_cache_enable_mutex); |
| 250 | return 0; |
| 251 | } |
| 252 | |
| 253 | /* called with swap slot cache's alloc lock held */ |
| 254 | static int refill_swap_slots_cache(struct swap_slots_cache *cache) |
| 255 | { |
| 256 | if (!use_swap_slot_cache || cache->nr) |
| 257 | return 0; |
| 258 | |
| 259 | cache->cur = 0; |
| 260 | if (swap_slot_cache_active) |
| 261 | cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE, cache->slots); |
| 262 | |
| 263 | return cache->nr; |
| 264 | } |
| 265 | |
| 266 | int free_swap_slot(swp_entry_t entry) |
| 267 | { |
| 268 | struct swap_slots_cache *cache; |
| 269 | |
Tim Chen | 67afa38 | 2017-02-22 15:45:39 -0800 | [diff] [blame] | 270 | cache = &get_cpu_var(swp_slots); |
| 271 | if (use_swap_slot_cache && cache->slots_ret) { |
| 272 | spin_lock_irq(&cache->free_lock); |
| 273 | /* Swap slots cache may be deactivated before acquiring lock */ |
| 274 | if (!use_swap_slot_cache) { |
| 275 | spin_unlock_irq(&cache->free_lock); |
| 276 | goto direct_free; |
| 277 | } |
| 278 | if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) { |
| 279 | /* |
| 280 | * Return slots to global pool. |
| 281 | * The current swap_map value is SWAP_HAS_CACHE. |
| 282 | * Set it to 0 to indicate it is available for |
| 283 | * allocation in global pool |
| 284 | */ |
| 285 | swapcache_free_entries(cache->slots_ret, cache->n_ret); |
| 286 | cache->n_ret = 0; |
| 287 | } |
| 288 | cache->slots_ret[cache->n_ret++] = entry; |
| 289 | spin_unlock_irq(&cache->free_lock); |
| 290 | } else { |
| 291 | direct_free: |
| 292 | swapcache_free_entries(&entry, 1); |
| 293 | } |
| 294 | put_cpu_var(swp_slots); |
| 295 | |
| 296 | return 0; |
| 297 | } |
| 298 | |
| 299 | swp_entry_t get_swap_page(void) |
| 300 | { |
| 301 | swp_entry_t entry, *pentry; |
| 302 | struct swap_slots_cache *cache; |
| 303 | |
| 304 | /* |
| 305 | * Preemption is allowed here, because we may sleep |
| 306 | * in refill_swap_slots_cache(). But it is safe, because |
| 307 | * accesses to the per-CPU data structure are protected by the |
| 308 | * mutex cache->alloc_lock. |
| 309 | * |
| 310 | * The alloc path here does not touch cache->slots_ret |
| 311 | * so cache->free_lock is not taken. |
| 312 | */ |
| 313 | cache = raw_cpu_ptr(&swp_slots); |
| 314 | |
| 315 | entry.val = 0; |
| 316 | if (check_cache_active()) { |
| 317 | mutex_lock(&cache->alloc_lock); |
| 318 | if (cache->slots) { |
| 319 | repeat: |
| 320 | if (cache->nr) { |
| 321 | pentry = &cache->slots[cache->cur++]; |
| 322 | entry = *pentry; |
| 323 | pentry->val = 0; |
| 324 | cache->nr--; |
| 325 | } else { |
| 326 | if (refill_swap_slots_cache(cache)) |
| 327 | goto repeat; |
| 328 | } |
| 329 | } |
| 330 | mutex_unlock(&cache->alloc_lock); |
| 331 | if (entry.val) |
| 332 | return entry; |
| 333 | } |
| 334 | |
| 335 | get_swap_pages(1, &entry); |
| 336 | |
| 337 | return entry; |
| 338 | } |
| 339 | |
| 340 | #endif /* CONFIG_SWAP */ |