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 /*
  34  * Number of tags we move between the percpu freelist and the global freelist at
  35  * a time
  36  */
  37 #define IDA_PCPU_BATCH_MOVE     32U
  38
  39 /* Max size of percpu freelist, */
  40 #define IDA_PCPU_SIZE           ((IDA_PCPU_BATCH_MOVE * 3) / 2)
  41
  42 struct percpu_ida_cpu {
  43         /*
  44          * Even though this is percpu, we need a lock for tag stealing by remote
  45          * CPUs:
  46          */
  47         spinlock_t                      lock;
  48
  49         /* nr_free/freelist form a stack of free IDs */
  50         unsigned                        nr_free;
  51         unsigned                        freelist[];
  52 };
  53
  54 static inline void move_tags(unsigned *dst, unsigned *dst_nr,
  55                              unsigned *src, unsigned *src_nr,
  56                              unsigned nr)
  57 {
  58         *src_nr -= nr;
  59         memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
  60         *dst_nr += nr;
  61 }
  62
  63 /*
  64  * Try to steal tags from a remote cpu's percpu freelist.
  65  *
  66  * We first check how many percpu freelists have tags - we don't steal tags
  67  * unless enough percpu freelists have tags on them that it's possible more than
  68  * half the total tags could be stuck on remote percpu freelists.
  69  *
  70  * Then we iterate through the cpus until we find some tags - we don't attempt
  71  * to find the "best" cpu to steal from, to keep cacheline bouncing to a
  72  * minimum.
  73  */
  74 static inline void steal_tags(struct percpu_ida *pool,
  75                               struct percpu_ida_cpu *tags)
  76 {
  77         unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
  78         struct percpu_ida_cpu *remote;
  79
  80         for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
  81              cpus_have_tags * IDA_PCPU_SIZE > pool->nr_tags / 2;
  82              cpus_have_tags--) {
  83                 cpu = cpumask_next(cpu, &pool->cpus_have_tags);
  84
  85                 if (cpu >= nr_cpu_ids) {
  86                         cpu = cpumask_first(&pool->cpus_have_tags);
  87                         if (cpu >= nr_cpu_ids)
  88                                 BUG();
  89                 }
  90
  91                 pool->cpu_last_stolen = cpu;
  92                 remote = per_cpu_ptr(pool->tag_cpu, cpu);
  93
  94                 cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
  95
  96                 if (remote == tags)
  97                         continue;
  98
  99                 spin_lock(&remote->lock);
 100
 101                 if (remote->nr_free) {
 102                         memcpy(tags->freelist,
 103                                remote->freelist,
 104                                sizeof(unsigned) * remote->nr_free);
 105
 106                         tags->nr_free = remote->nr_free;
 107                         remote->nr_free = 0;
 108                 }
 109
 110                 spin_unlock(&remote->lock);
 111
 112                 if (tags->nr_free)
 113                         break;
 114         }
 115 }
 116
 117 /*
 118  * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
 119  * our percpu freelist:
 120  */
 121 static inline void alloc_global_tags(struct percpu_ida *pool,
 122                                      struct percpu_ida_cpu *tags)
 123 {
 124         move_tags(tags->freelist, &tags->nr_free,
 125                   pool->freelist, &pool->nr_free,
 126                   min(pool->nr_free, IDA_PCPU_BATCH_MOVE));
 127 }
 128
 129 static inline unsigned alloc_local_tag(struct percpu_ida *pool,
 130                                        struct percpu_ida_cpu *tags)
 131 {
 132         int tag = -ENOSPC;
 133
 134         spin_lock(&tags->lock);
 135         if (tags->nr_free)
 136                 tag = tags->freelist[--tags->nr_free];
 137         spin_unlock(&tags->lock);
 138
 139         return tag;
 140 }
 141
 142 /**
 143  * percpu_ida_alloc - allocate a tag
 144  * @pool: pool to allocate from
 145  * @gfp: gfp flags
 146  *
 147  * Returns a tag - an integer in the range [0..nr_tags) (passed to
 148  * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
 149  *
 150  * Safe to be called from interrupt context (assuming it isn't passed
 151  * __GFP_WAIT, of course).
 152  *
 153  * @gfp indicates whether or not to wait until a free id is available (it's not
 154  * used for internal memory allocations); thus if passed __GFP_WAIT we may sleep
 155  * however long it takes until another thread frees an id (same semantics as a
 156  * mempool).
 157  *
 158  * Will not fail if passed __GFP_WAIT.
 159  */
 160 int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp)
 161 {
 162         DEFINE_WAIT(wait);
 163         struct percpu_ida_cpu *tags;
 164         unsigned long flags;
 165         int tag;
 166
 167         local_irq_save(flags);
 168         tags = this_cpu_ptr(pool->tag_cpu);
 169
 170         /* Fastpath */
 171         tag = alloc_local_tag(pool, tags);
 172         if (likely(tag >= 0)) {
 173                 local_irq_restore(flags);
 174                 return tag;
 175         }
 176
 177         while (1) {
 178                 spin_lock(&pool->lock);
 179
 180                 /*
 181                  * prepare_to_wait() must come before steal_tags(), in case
 182                  * percpu_ida_free() on another cpu flips a bit in
 183                  * cpus_have_tags
 184                  *
 185                  * global lock held and irqs disabled, don't need percpu lock
 186                  */
 187                 prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
 188
 189                 if (!tags->nr_free)
 190                         alloc_global_tags(pool, tags);
 191                 if (!tags->nr_free)
 192                         steal_tags(pool, tags);
 193
 194                 if (tags->nr_free) {
 195                         tag = tags->freelist[--tags->nr_free];
 196                         if (tags->nr_free)
 197                                 cpumask_set_cpu(smp_processor_id(),
 198                                                 &pool->cpus_have_tags);
 199                 }
 200
 201                 spin_unlock(&pool->lock);
 202                 local_irq_restore(flags);
 203
 204                 if (tag >= 0 || !(gfp & __GFP_WAIT))
 205                         break;
 206
 207                 schedule();
 208
 209                 local_irq_save(flags);
 210                 tags = this_cpu_ptr(pool->tag_cpu);
 211         }
 212
 213         finish_wait(&pool->wait, &wait);
 214         return tag;
 215 }
 216 EXPORT_SYMBOL_GPL(percpu_ida_alloc);
 217
 218 /**
 219  * percpu_ida_free - free a tag
 220  * @pool: pool @tag was allocated from
 221  * @tag: a tag previously allocated with percpu_ida_alloc()
 222  *
 223  * Safe to be called from interrupt context.
 224  */
 225 void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
 226 {
 227         struct percpu_ida_cpu *tags;
 228         unsigned long flags;
 229         unsigned nr_free;
 230
 231         BUG_ON(tag >= pool->nr_tags);
 232
 233         local_irq_save(flags);
 234         tags = this_cpu_ptr(pool->tag_cpu);
 235
 236         spin_lock(&tags->lock);
 237         tags->freelist[tags->nr_free++] = tag;
 238
 239         nr_free = tags->nr_free;
 240         spin_unlock(&tags->lock);
 241
 242         if (nr_free == 1) {
 243                 cpumask_set_cpu(smp_processor_id(),
 244                                 &pool->cpus_have_tags);
 245                 wake_up(&pool->wait);
 246         }
 247
 248         if (nr_free == IDA_PCPU_SIZE) {
 249                 spin_lock(&pool->lock);
 250
 251                 /*
 252                  * Global lock held and irqs disabled, don't need percpu
 253                  * lock
 254                  */
 255                 if (tags->nr_free == IDA_PCPU_SIZE) {
 256                         move_tags(pool->freelist, &pool->nr_free,
 257                                   tags->freelist, &tags->nr_free,
 258                                   IDA_PCPU_BATCH_MOVE);
 259
 260                         wake_up(&pool->wait);
 261                 }
 262                 spin_unlock(&pool->lock);
 263         }
 264
 265         local_irq_restore(flags);
 266 }
 267 EXPORT_SYMBOL_GPL(percpu_ida_free);
 268
 269 /**
 270  * percpu_ida_destroy - release a tag pool's resources
 271  * @pool: pool to free
 272  *
 273  * Frees the resources allocated by percpu_ida_init().
 274  */
 275 void percpu_ida_destroy(struct percpu_ida *pool)
 276 {
 277         free_percpu(pool->tag_cpu);
 278         free_pages((unsigned long) pool->freelist,
 279                    get_order(pool->nr_tags * sizeof(unsigned)));
 280 }
 281 EXPORT_SYMBOL_GPL(percpu_ida_destroy);
 282
 283 /**
 284  * percpu_ida_init - initialize a percpu tag pool
 285  * @pool: pool to initialize
 286  * @nr_tags: number of tags that will be available for allocation
 287  *
 288  * Initializes @pool so that it can be used to allocate tags - integers in the
 289  * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
 290  * preallocated array of tag structures.
 291  *
 292  * Allocation is percpu, but sharding is limited by nr_tags - for best
 293  * performance, the workload should not span more cpus than nr_tags / 128.
 294  */
 295 int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags)
 296 {
 297         unsigned i, cpu, order;
 298
 299         memset(pool, 0, sizeof(*pool));
 300
 301         init_waitqueue_head(&pool->wait);
 302         spin_lock_init(&pool->lock);
 303         pool->nr_tags = nr_tags;
 304
 305         /* Guard against overflow */
 306         if (nr_tags > (unsigned) INT_MAX + 1) {
 307                 pr_err("percpu_ida_init(): nr_tags too large\n");
 308                 return -EINVAL;
 309         }
 310
 311         order = get_order(nr_tags * sizeof(unsigned));
 312         pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
 313         if (!pool->freelist)
 314                 return -ENOMEM;
 315
 316         for (i = 0; i < nr_tags; i++)
 317                 pool->freelist[i] = i;
 318
 319         pool->nr_free = nr_tags;
 320
 321         pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
 322                                        IDA_PCPU_SIZE * sizeof(unsigned),
 323                                        sizeof(unsigned));
 324         if (!pool->tag_cpu)
 325                 goto err;
 326
 327         for_each_possible_cpu(cpu)
 328                 spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
 329
 330         return 0;
 331 err:
 332         percpu_ida_destroy(pool);
 333         return -ENOMEM;
 334 }
 335 EXPORT_SYMBOL_GPL(percpu_ida_init);