cregit-Linux how code gets into the kernel

Release 4.7 lib/percpu_ida.c

Directory: lib
 * 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
 * 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/init.h>
#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/percpu_ida.h>

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; }


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/* * Try to steal tags from a remote cpu's percpu freelist. * * We first check how many percpu freelists have tags * * 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; 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; } }


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/* * 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, pool->percpu_batch_size)); }


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static inline unsigned alloc_local_tag(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; }


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/** * percpu_ida_alloc - allocate a tag * @pool: pool to allocate from * @state: task state for prepare_to_wait * * 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 * TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 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_RECLAIM we may sleep * however long it takes until another thread frees an id (same semantics as a * mempool). * * Will not fail if passed TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE. */
int percpu_ida_alloc(struct percpu_ida *pool, int state) { 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(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 */ if (state != TASK_RUNNING) prepare_to_wait(&pool->wait, &wait, state); 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 || state == TASK_RUNNING) break; if (signal_pending_state(state, current)) { tag = -ERESTARTSYS; break; } schedule(); local_irq_save(flags); tags = this_cpu_ptr(pool->tag_cpu); } if (state != TASK_RUNNING) finish_wait(&pool->wait, &wait); return tag; }


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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 == pool->percpu_max_size) { spin_lock(&pool->lock); /* * Global lock held and irqs disabled, don't need percpu * lock */ if (tags->nr_free == pool->percpu_max_size) { move_tags(pool->freelist, &pool->nr_free, tags->freelist, &tags->nr_free, pool->percpu_batch_size); wake_up(&pool->wait); } spin_unlock(&pool->lock); } local_irq_restore(flags); }


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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))); }


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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 long max_size, unsigned long batch_size) { unsigned i, cpu, order; memset(pool, 0, sizeof(*pool)); init_waitqueue_head(&pool->wait); spin_lock_init(&pool->lock); pool->nr_tags = nr_tags; pool->percpu_max_size = max_size; pool->percpu_batch_size = batch_size; /* 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) + pool->percpu_max_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; }


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EXPORT_SYMBOL_GPL(__percpu_ida_init); /** * percpu_ida_for_each_free - iterate free ids of a pool * @pool: pool to iterate * @fn: interate callback function * @data: parameter for @fn * * Note, this doesn't guarantee to iterate all free ids restrictly. Some free * ids might be missed, some might be iterated duplicated, and some might * be iterated and not free soon. */
int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn, void *data) { unsigned long flags; struct percpu_ida_cpu *remote; unsigned cpu, i, err = 0; local_irq_save(flags); for_each_possible_cpu(cpu) { remote = per_cpu_ptr(pool->tag_cpu, cpu); spin_lock(&remote->lock); for (i = 0; i < remote->nr_free; i++) { err = fn(remote->freelist[i], data); if (err) break; } spin_unlock(&remote->lock); if (err) goto out; } spin_lock(&pool->lock); for (i = 0; i < pool->nr_free; i++) { err = fn(pool->freelist[i], data); if (err) break; } spin_unlock(&pool->lock); out: local_irq_restore(flags); return err; }


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EXPORT_SYMBOL_GPL(percpu_ida_for_each_free); /** * percpu_ida_free_tags - return free tags number of a specific cpu or global pool * @pool: pool related * @cpu: specific cpu or global pool if @cpu == nr_cpu_ids * * Note: this just returns a snapshot of free tags number. */
unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu) { struct percpu_ida_cpu *remote; if (cpu == nr_cpu_ids) return pool->nr_free; remote = per_cpu_ptr(pool->tag_cpu, cpu); return remote->nr_free; }


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Directory: lib
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