1 files changed, 335 insertions, 0 deletions

diff --git a/lib/percpu_ida.c b/lib/percpu_ida.c
new file mode 100644
index 000000000000..bab1ba2a4c71
--- /dev/null
+++ b/lib/percpu_ida.c
@@ -0,0 +1,335 @@
+/*
+ * Percpu IDA library
+ *
+ * Copyright (C) 2013 Datera, Inc. Kent Overstreet
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/bitmap.h>
+#include <linux/bitops.h>
+#include <linux/bug.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/hardirq.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/spinlock.h>
+#include <linux/percpu_ida.h>
+
+/*
+ * Number of tags we move between the percpu freelist and the global freelist at
+ * a time
+ */
+#define IDA_PCPU_BATCH_MOVE     32U
+
+/* Max size of percpu freelist, */
+#define IDA_PCPU_SIZE           ((IDA_PCPU_BATCH_MOVE * 3) / 2)
+
+struct percpu_ida_cpu {
+        /*
+         * Even though this is percpu, we need a lock for tag stealing by remote
+         * CPUs:
+         */
+        spinlock_t                      lock;
+
+        /* nr_free/freelist form a stack of free IDs */
+        unsigned                        nr_free;
+        unsigned                        freelist[];
+};
+
+static inline void move_tags(unsigned *dst, unsigned *dst_nr,
+                             unsigned *src, unsigned *src_nr,
+                             unsigned nr)
+{
+        *src_nr -= nr;
+        memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
+        *dst_nr += nr;
+}
+
+/*
+ * Try to steal tags from a remote cpu's percpu freelist.
+ *
+ * We first check how many percpu freelists have tags - we don't steal tags
+ * unless enough percpu freelists have tags on them that it's possible more than
+ * half the total tags could be stuck on remote percpu freelists.
+ *
+ * Then we iterate through the cpus until we find some tags - we don't attempt
+ * to find the "best" cpu to steal from, to keep cacheline bouncing to a
+ * minimum.
+ */
+static inline void steal_tags(struct percpu_ida *pool,
+                              struct percpu_ida_cpu *tags)
+{
+        unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
+        struct percpu_ida_cpu *remote;
+
+        for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
+             cpus_have_tags * IDA_PCPU_SIZE > pool->nr_tags / 2;
+             cpus_have_tags--) {
+                cpu = cpumask_next(cpu, &pool->cpus_have_tags);
+
+                if (cpu >= nr_cpu_ids) {
+                        cpu = cpumask_first(&pool->cpus_have_tags);
+                        if (cpu >= nr_cpu_ids)
+                                BUG();
+                }
+
+                pool->cpu_last_stolen = cpu;
+                remote = per_cpu_ptr(pool->tag_cpu, cpu);
+
+                cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
+
+                if (remote == tags)
+                        continue;
+
+                spin_lock(&remote->lock);
+
+                if (remote->nr_free) {
+                        memcpy(tags->freelist,
+                               remote->freelist,
+                               sizeof(unsigned) * remote->nr_free);
+
+                        tags->nr_free = remote->nr_free;
+                        remote->nr_free = 0;
+                }
+
+                spin_unlock(&remote->lock);
+
+                if (tags->nr_free)
+                        break;
+        }
+}
+
+/*
+ * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
+ * our percpu freelist:
+ */
+static inline void alloc_global_tags(struct percpu_ida *pool,
+                                     struct percpu_ida_cpu *tags)
+{
+        move_tags(tags->freelist, &tags->nr_free,
+                  pool->freelist, &pool->nr_free,
+                  min(pool->nr_free, IDA_PCPU_BATCH_MOVE));
+}
+
+static inline unsigned alloc_local_tag(struct percpu_ida *pool,
+                                       struct percpu_ida_cpu *tags)
+{
+        int tag = -ENOSPC;
+
+        spin_lock(&tags->lock);
+        if (tags->nr_free)
+                tag = tags->freelist[--tags->nr_free];
+        spin_unlock(&tags->lock);
+
+        return tag;
+}
+
+/**
+ * percpu_ida_alloc - allocate a tag
+ * @pool: pool to allocate from
+ * @gfp: gfp flags
+ *
+ * Returns a tag - an integer in the range [0..nr_tags) (passed to
+ * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
+ *
+ * Safe to be called from interrupt context (assuming it isn't passed
+ * __GFP_WAIT, of course).
+ *
+ * @gfp indicates whether or not to wait until a free id is available (it's not
+ * used for internal memory allocations); thus if passed __GFP_WAIT we may sleep
+ * however long it takes until another thread frees an id (same semantics as a
+ * mempool).
+ *
+ * Will not fail if passed __GFP_WAIT.
+ */
+int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp)
+{
+        DEFINE_WAIT(wait);
+        struct percpu_ida_cpu *tags;
+        unsigned long flags;
+        int tag;
+
+        local_irq_save(flags);
+        tags = this_cpu_ptr(pool->tag_cpu);
+
+        /* Fastpath */
+        tag = alloc_local_tag(pool, tags);
+        if (likely(tag >= 0)) {
+                local_irq_restore(flags);
+                return tag;
+        }
+
+        while (1) {
+                spin_lock(&pool->lock);
+
+                /*
+                 * prepare_to_wait() must come before steal_tags(), in case
+                 * percpu_ida_free() on another cpu flips a bit in
+                 * cpus_have_tags
+                 *
+                 * global lock held and irqs disabled, don't need percpu lock
+                 */
+                prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
+
+                if (!tags->nr_free)
+                        alloc_global_tags(pool, tags);
+                if (!tags->nr_free)
+                        steal_tags(pool, tags);
+
+                if (tags->nr_free) {
+                        tag = tags->freelist[--tags->nr_free];
+                        if (tags->nr_free)
+                                cpumask_set_cpu(smp_processor_id(),
+                                                &pool->cpus_have_tags);
+                }
+
+                spin_unlock(&pool->lock);
+                local_irq_restore(flags);
+
+                if (tag >= 0 || !(gfp & __GFP_WAIT))
+                        break;
+
+                schedule();
+
+                local_irq_save(flags);
+                tags = this_cpu_ptr(pool->tag_cpu);
+        }
+
+        finish_wait(&pool->wait, &wait);
+        return tag;
+}
+EXPORT_SYMBOL_GPL(percpu_ida_alloc);
+
+/**
+ * percpu_ida_free - free a tag
+ * @pool: pool @tag was allocated from
+ * @tag: a tag previously allocated with percpu_ida_alloc()
+ *
+ * Safe to be called from interrupt context.
+ */
+void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
+{
+        struct percpu_ida_cpu *tags;
+        unsigned long flags;
+        unsigned nr_free;
+
+        BUG_ON(tag >= pool->nr_tags);
+
+        local_irq_save(flags);
+        tags = this_cpu_ptr(pool->tag_cpu);
+
+        spin_lock(&tags->lock);
+        tags->freelist[tags->nr_free++] = tag;
+
+        nr_free = tags->nr_free;
+        spin_unlock(&tags->lock);
+
+        if (nr_free == 1) {
+                cpumask_set_cpu(smp_processor_id(),
+                                &pool->cpus_have_tags);
+                wake_up(&pool->wait);
+        }
+
+        if (nr_free == IDA_PCPU_SIZE) {
+                spin_lock(&pool->lock);
+
+                /*
+                 * Global lock held and irqs disabled, don't need percpu
+                 * lock
+                 */
+                if (tags->nr_free == IDA_PCPU_SIZE) {
+                        move_tags(pool->freelist, &pool->nr_free,
+                                  tags->freelist, &tags->nr_free,
+                                  IDA_PCPU_BATCH_MOVE);
+
+                        wake_up(&pool->wait);
+                }
+                spin_unlock(&pool->lock);
+        }
+
+        local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(percpu_ida_free);
+
+/**
+ * percpu_ida_destroy - release a tag pool's resources
+ * @pool: pool to free
+ *
+ * Frees the resources allocated by percpu_ida_init().
+ */
+void percpu_ida_destroy(struct percpu_ida *pool)
+{
+        free_percpu(pool->tag_cpu);
+        free_pages((unsigned long) pool->freelist,
+                   get_order(pool->nr_tags * sizeof(unsigned)));
+}
+EXPORT_SYMBOL_GPL(percpu_ida_destroy);
+
+/**
+ * percpu_ida_init - initialize a percpu tag pool
+ * @pool: pool to initialize
+ * @nr_tags: number of tags that will be available for allocation
+ *
+ * Initializes @pool so that it can be used to allocate tags - integers in the
+ * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
+ * preallocated array of tag structures.
+ *
+ * Allocation is percpu, but sharding is limited by nr_tags - for best
+ * performance, the workload should not span more cpus than nr_tags / 128.
+ */
+int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags)
+{
+        unsigned i, cpu, order;
+
+        memset(pool, 0, sizeof(*pool));
+
+        init_waitqueue_head(&pool->wait);
+        spin_lock_init(&pool->lock);
+        pool->nr_tags = nr_tags;
+
+        /* Guard against overflow */
+        if (nr_tags > (unsigned) INT_MAX + 1) {
+                pr_err("percpu_ida_init(): nr_tags too large\n");
+                return -EINVAL;
+        }
+
+        order = get_order(nr_tags * sizeof(unsigned));
+        pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
+        if (!pool->freelist)
+                return -ENOMEM;
+
+        for (i = 0; i < nr_tags; i++)
+                pool->freelist[i] = i;
+
+        pool->nr_free = nr_tags;
+
+        pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
+                                       IDA_PCPU_SIZE * sizeof(unsigned),
+                                       sizeof(unsigned));
+        if (!pool->tag_cpu)
+                goto err;
+
+        for_each_possible_cpu(cpu)
+                spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
+
+        return 0;
+err:
+        percpu_ida_destroy(pool);
+        return -ENOMEM;
+}
+EXPORT_SYMBOL_GPL(percpu_ida_init);