lib/percpu_ida.c

   1 /*
   2  * Percpu IDA library
   3  *
   4  * Copyright (C) 2013 Datera, Inc. Kent Overstreet
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 2, or (at
   9  * your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  */
  16
  17 #include <linux/mm.h>
  18 #include <linux/bitmap.h>
  19 #include <linux/bitops.h>
  20 #include <linux/bug.h>
  21 #include <linux/err.h>
  22 #include <linux/export.h>
  23 #include <linux/init.h>
  24 #include <linux/kernel.h>
  25 #include <linux/percpu.h>
  26 #include <linux/sched/signal.h>
  27 #include <linux/string.h>
  28 #include <linux/spinlock.h>
  29 #include <linux/percpu_ida.h>
  30
  31 struct percpu_ida_cpu {
  32         /*
  33          * Even though this is percpu, we need a lock for tag stealing by remote
  34          * CPUs:
  35          */
  36         spinlock_t                      lock;
  37
  38         /* nr_free/freelist form a stack of free IDs */
  39         unsigned                        nr_free;
  40         unsigned                        freelist[];
  41 };
  42
  43 static inline void move_tags(unsigned *dst, unsigned *dst_nr,
  44                              unsigned *src, unsigned *src_nr,
  45                              unsigned nr)
  46 {
  47         *src_nr -= nr;
  48         memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
  49         *dst_nr += nr;
  50 }
  51
  52 /*
  53  * Try to steal tags from a remote cpu's percpu freelist.
  54  *
  55  * We first check how many percpu freelists have tags
  56  *
  57  * Then we iterate through the cpus until we find some tags - we don't attempt
  58  * to find the "best" cpu to steal from, to keep cacheline bouncing to a
  59  * minimum.
  60  */
  61 static inline void steal_tags(struct percpu_ida *pool,
  62                               struct percpu_ida_cpu *tags)
  63 {
  64         unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
  65         struct percpu_ida_cpu *remote;
  66
  67         for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
  68              cpus_have_tags; cpus_have_tags--) {
  69                 cpu = cpumask_next(cpu, &pool->cpus_have_tags);
  70
  71                 if (cpu >= nr_cpu_ids) {
  72                         cpu = cpumask_first(&pool->cpus_have_tags);
  73                         if (cpu >= nr_cpu_ids)
  74                                 BUG();
  75                 }
  76
  77                 pool->cpu_last_stolen = cpu;
  78                 remote = per_cpu_ptr(pool->tag_cpu, cpu);
  79
  80                 cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
  81
  82                 if (remote == tags)
  83                         continue;
  84
  85                 spin_lock(&remote->lock);
  86
  87                 if (remote->nr_free) {
  88                         memcpy(tags->freelist,
  89                                remote->freelist,
  90                                sizeof(unsigned) * remote->nr_free);
  91
  92                         tags->nr_free = remote->nr_free;
  93                         remote->nr_free = 0;
  94                 }
  95
  96                 spin_unlock(&remote->lock);
  97
  98                 if (tags->nr_free)
  99                         break;
 100         }
 101 }
 102
 103 /*
 104  * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
 105  * our percpu freelist:
 106  */
 107 static inline void alloc_global_tags(struct percpu_ida *pool,
 108                                      struct percpu_ida_cpu *tags)
 109 {
 110         move_tags(tags->freelist, &tags->nr_free,
 111                   pool->freelist, &pool->nr_free,
 112                   min(pool->nr_free, pool->percpu_batch_size));
 113 }
 114
 115 static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
 116 {
 117         int tag = -ENOSPC;
 118
 119         spin_lock(&tags->lock);
 120         if (tags->nr_free)
 121                 tag = tags->freelist[--tags->nr_free];
 122         spin_unlock(&tags->lock);
 123
 124         return tag;
 125 }
 126
 127 /**
 128  * percpu_ida_alloc - allocate a tag
 129  * @pool: pool to allocate from
 130  * @state: task state for prepare_to_wait
 131  *
 132  * Returns a tag - an integer in the range [0..nr_tags) (passed to
 133  * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
 134  *
 135  * Safe to be called from interrupt context (assuming it isn't passed
 136  * TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, of course).
 137  *
 138  * @gfp indicates whether or not to wait until a free id is available (it's not
 139  * used for internal memory allocations); thus if passed __GFP_RECLAIM we may sleep
 140  * however long it takes until another thread frees an id (same semantics as a
 141  * mempool).
 142  *
 143  * Will not fail if passed TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE.
 144  */
 145 int percpu_ida_alloc(struct percpu_ida *pool, int state)
 146 {
 147         DEFINE_WAIT(wait);
 148         struct percpu_ida_cpu *tags;
 149         unsigned long flags;
 150         int tag;
 151
 152         local_irq_save(flags);
 153         tags = this_cpu_ptr(pool->tag_cpu);
 154
 155         /* Fastpath */
 156         tag = alloc_local_tag(tags);
 157         if (likely(tag >= 0)) {
 158                 local_irq_restore(flags);
 159                 return tag;
 160         }
 161
 162         while (1) {
 163                 spin_lock(&pool->lock);
 164
 165                 /*
 166                  * prepare_to_wait() must come before steal_tags(), in case
 167                  * percpu_ida_free() on another cpu flips a bit in
 168                  * cpus_have_tags
 169                  *
 170                  * global lock held and irqs disabled, don't need percpu lock
 171                  */
 172                 if (state != TASK_RUNNING)
 173                         prepare_to_wait(&pool->wait, &wait, state);
 174
 175                 if (!tags->nr_free)
 176                         alloc_global_tags(pool, tags);
 177                 if (!tags->nr_free)
 178                         steal_tags(pool, tags);
 179
 180                 if (tags->nr_free) {
 181                         tag = tags->freelist[--tags->nr_free];
 182                         if (tags->nr_free)
 183                                 cpumask_set_cpu(smp_processor_id(),
 184                                                 &pool->cpus_have_tags);
 185                 }
 186
 187                 spin_unlock(&pool->lock);
 188                 local_irq_restore(flags);
 189
 190                 if (tag >= 0 || state == TASK_RUNNING)
 191                         break;
 192
 193                 if (signal_pending_state(state, current)) {
 194                         tag = -ERESTARTSYS;
 195                         break;
 196                 }
 197
 198                 schedule();
 199
 200                 local_irq_save(flags);
 201                 tags = this_cpu_ptr(pool->tag_cpu);
 202         }
 203         if (state != TASK_RUNNING)
 204                 finish_wait(&pool->wait, &wait);
 205
 206         return tag;
 207 }
 208 EXPORT_SYMBOL_GPL(percpu_ida_alloc);
 209
 210 /**
 211  * percpu_ida_free - free a tag
 212  * @pool: pool @tag was allocated from
 213  * @tag: a tag previously allocated with percpu_ida_alloc()
 214  *
 215  * Safe to be called from interrupt context.
 216  */
 217 void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
 218 {
 219         struct percpu_ida_cpu *tags;
 220         unsigned long flags;
 221         unsigned nr_free;
 222
 223         BUG_ON(tag >= pool->nr_tags);
 224
 225         local_irq_save(flags);
 226         tags = this_cpu_ptr(pool->tag_cpu);
 227
 228         spin_lock(&tags->lock);
 229         tags->freelist[tags->nr_free++] = tag;
 230
 231         nr_free = tags->nr_free;
 232         spin_unlock(&tags->lock);
 233
 234         if (nr_free == 1) {
 235                 cpumask_set_cpu(smp_processor_id(),
 236                                 &pool->cpus_have_tags);
 237                 wake_up(&pool->wait);
 238         }
 239
 240         if (nr_free == pool->percpu_max_size) {
 241                 spin_lock(&pool->lock);
 242
 243                 /*
 244                  * Global lock held and irqs disabled, don't need percpu
 245                  * lock
 246                  */
 247                 if (tags->nr_free == pool->percpu_max_size) {
 248                         move_tags(pool->freelist, &pool->nr_free,
 249                                   tags->freelist, &tags->nr_free,
 250                                   pool->percpu_batch_size);
 251
 252                         wake_up(&pool->wait);
 253                 }
 254                 spin_unlock(&pool->lock);
 255         }
 256
 257         local_irq_restore(flags);
 258 }
 259 EXPORT_SYMBOL_GPL(percpu_ida_free);
 260
 261 /**
 262  * percpu_ida_destroy - release a tag pool's resources
 263  * @pool: pool to free
 264  *
 265  * Frees the resources allocated by percpu_ida_init().
 266  */
 267 void percpu_ida_destroy(struct percpu_ida *pool)
 268 {
 269         free_percpu(pool->tag_cpu);
 270         free_pages((unsigned long) pool->freelist,
 271                    get_order(pool->nr_tags * sizeof(unsigned)));
 272 }
 273 EXPORT_SYMBOL_GPL(percpu_ida_destroy);
 274
 275 /**
 276  * percpu_ida_init - initialize a percpu tag pool
 277  * @pool: pool to initialize
 278  * @nr_tags: number of tags that will be available for allocation
 279  *
 280  * Initializes @pool so that it can be used to allocate tags - integers in the
 281  * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
 282  * preallocated array of tag structures.
 283  *
 284  * Allocation is percpu, but sharding is limited by nr_tags - for best
 285  * performance, the workload should not span more cpus than nr_tags / 128.
 286  */
 287 int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
 288         unsigned long max_size, unsigned long batch_size)
 289 {
 290         unsigned i, cpu, order;
 291
 292         memset(pool, 0, sizeof(*pool));
 293
 294         init_waitqueue_head(&pool->wait);
 295         spin_lock_init(&pool->lock);
 296         pool->nr_tags = nr_tags;
 297         pool->percpu_max_size = max_size;
 298         pool->percpu_batch_size = batch_size;
 299
 300         /* Guard against overflow */
 301         if (nr_tags > (unsigned) INT_MAX + 1) {
 302                 pr_err("percpu_ida_init(): nr_tags too large\n");
 303                 return -EINVAL;
 304         }
 305
 306         order = get_order(nr_tags * sizeof(unsigned));
 307         pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
 308         if (!pool->freelist)
 309                 return -ENOMEM;
 310
 311         for (i = 0; i < nr_tags; i++)
 312                 pool->freelist[i] = i;
 313
 314         pool->nr_free = nr_tags;
 315
 316         pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
 317                                        pool->percpu_max_size * sizeof(unsigned),
 318                                        sizeof(unsigned));
 319         if (!pool->tag_cpu)
 320                 goto err;
 321
 322         for_each_possible_cpu(cpu)
 323                 spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
 324
 325         return 0;
 326 err:
 327         percpu_ida_destroy(pool);
 328         return -ENOMEM;
 329 }
 330 EXPORT_SYMBOL_GPL(__percpu_ida_init);
 331
 332 /**
 333  * percpu_ida_for_each_free - iterate free ids of a pool
 334  * @pool: pool to iterate
 335  * @fn: interate callback function
 336  * @data: parameter for @fn
 337  *
 338  * Note, this doesn't guarantee to iterate all free ids restrictly. Some free
 339  * ids might be missed, some might be iterated duplicated, and some might
 340  * be iterated and not free soon.
 341  */
 342 int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
 343         void *data)
 344 {
 345         unsigned long flags;
 346         struct percpu_ida_cpu *remote;
 347         unsigned cpu, i, err = 0;
 348
 349         local_irq_save(flags);
 350         for_each_possible_cpu(cpu) {
 351                 remote = per_cpu_ptr(pool->tag_cpu, cpu);
 352                 spin_lock(&remote->lock);
 353                 for (i = 0; i < remote->nr_free; i++) {
 354                         err = fn(remote->freelist[i], data);
 355                         if (err)
 356                                 break;
 357                 }
 358                 spin_unlock(&remote->lock);
 359                 if (err)
 360                         goto out;
 361         }
 362
 363         spin_lock(&pool->lock);
 364         for (i = 0; i < pool->nr_free; i++) {
 365                 err = fn(pool->freelist[i], data);
 366                 if (err)
 367                         break;
 368         }
 369         spin_unlock(&pool->lock);
 370 out:
 371         local_irq_restore(flags);
 372         return err;
 373 }
 374 EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
 375
 376 /**
 377  * percpu_ida_free_tags - return free tags number of a specific cpu or global pool
 378  * @pool: pool related
 379  * @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
 380  *
 381  * Note: this just returns a snapshot of free tags number.
 382  */
 383 unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
 384 {
 385         struct percpu_ida_cpu *remote;
 386         if (cpu == nr_cpu_ids)
 387                 return pool->nr_free;
 388         remote = per_cpu_ptr(pool->tag_cpu, cpu);
 389         return remote->nr_free;
 390 }
 391 EXPORT_SYMBOL_GPL(percpu_ida_free_tags);