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