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/*
* Functions related to io context handling
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/bootmem.h> /* for max_pfn/max_low_pfn */
#include <linux/slab.h>
#include "blk.h"
/*
* For io context allocations
*/
static struct kmem_cache *iocontext_cachep;
struct request *blk_ioc_get_cached_request(struct io_context *ioc)
{
struct request *rq = NULL;
/*
* See if there are available cached requests
*/
if (!list_empty_careful(&ioc->free_list)) {
spin_lock_irq(&ioc->lock);
if (!list_empty(&ioc->free_list)) {
rq = list_entry(ioc->free_list.next, struct request,
queuelist);
list_del_init(&rq->queuelist);
}
spin_unlock_irq(&ioc->lock);
}
return rq;
}
bool blk_ioc_cache_request(struct request_queue *q, struct io_context *ioc,
struct request *rq)
{
/*
* Don't cache something that came from the emergency pool
*/
if (rq->cmd_flags & REQ_MEMPOOL)
return false;
/*
* cache this request for reuse
*/
if ((rq->cmd_flags & REQ_ALLOCED) &&
(ioc->free_requests < 2 * q->nr_requests)) {
list_add(&rq->queuelist, &ioc->free_list);
return true;
}
return false;
}
static void cfq_dtor(struct io_context *ioc)
{
if (!hlist_empty(&ioc->cic_list)) {
struct cfq_io_context *cic;
cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
cic_list);
cic->dtor(ioc);
}
}
/*
* IO Context helper functions. put_io_context() returns 1 if there are no
* more users of this io context, 0 otherwise.
*/
int put_io_context(struct io_context *ioc)
{
if (ioc == NULL)
return 1;
BUG_ON(atomic_long_read(&ioc->refcount) == 0);
if (atomic_long_dec_and_test(&ioc->refcount)) {
rcu_read_lock();
cfq_dtor(ioc);
rcu_read_unlock();
/*
* free cached requests, if any. this is safe without the
* lock, since we are the only ones that are still holding
* a reference to it and others cannot grab a ref to it now.
*/
while (!list_empty(&ioc->free_list)) {
struct request *rq;
rq = list_entry(ioc->free_list.next, struct request,
queuelist);
list_del(&rq->queuelist);
blk_slab_free_request(rq);
}
kmem_cache_free(iocontext_cachep, ioc);
return 1;
}
return 0;
}
EXPORT_SYMBOL(put_io_context);
static void cfq_exit(struct io_context *ioc)
{
rcu_read_lock();
if (!hlist_empty(&ioc->cic_list)) {
struct cfq_io_context *cic;
cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
cic_list);
cic->exit(ioc);
}
rcu_read_unlock();
}
/* Called by the exiting task */
void exit_io_context(struct task_struct *task)
{
struct io_context *ioc;
task_lock(task);
ioc = task->io_context;
task->io_context = NULL;
task_unlock(task);
if (atomic_dec_and_test(&ioc->nr_tasks))
cfq_exit(ioc);
put_io_context(ioc);
}
struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
{
struct io_context *ret;
ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
if (ret) {
atomic_long_set(&ret->refcount, 1);
atomic_set(&ret->nr_tasks, 1);
spin_lock_init(&ret->lock);
ret->ioprio_changed = 0;
ret->ioprio = 0;
init_waitqueue_head(&ret->wait[BLK_RW_SYNC]);
init_waitqueue_head(&ret->wait[BLK_RW_ASYNC]);
INIT_LIST_HEAD(&ret->free_list);
ret->free_requests = 0;
ret->count[BLK_RW_SYNC] = ret->count[BLK_RW_ASYNC] = 0;
INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);
INIT_HLIST_HEAD(&ret->cic_list);
ret->ioc_data = NULL;
}
return ret;
}
/*
* If the current task has no IO context then create one and initialise it.
* Otherwise, return its existing IO context.
*
* This returned IO context doesn't have a specifically elevated refcount,
* but since the current task itself holds a reference, the context can be
* used in general code, so long as it stays within `current` context.
*/
struct io_context *current_io_context(gfp_t gfp_flags, int node)
{
struct task_struct *tsk = current;
struct io_context *ret;
ret = tsk->io_context;
if (likely(ret))
return ret;
ret = alloc_io_context(gfp_flags, node);
if (ret) {
/* make sure set_task_ioprio() sees the settings above */
smp_wmb();
tsk->io_context = ret;
}
return ret;
}
/*
* If the current task has no IO context then create one and initialise it.
* If it does have a context, take a ref on it.
*
* This is always called in the context of the task which submitted the I/O.
*/
struct io_context *get_io_context(gfp_t gfp_flags, int node)
{
struct io_context *ret = NULL;
/*
* Check for unlikely race with exiting task. ioc ref count is
* zero when ioc is being detached.
*/
do {
ret = current_io_context(gfp_flags, node);
if (unlikely(!ret))
break;
} while (!atomic_long_inc_not_zero(&ret->refcount));
return ret;
}
EXPORT_SYMBOL(get_io_context);
static int __init blk_ioc_init(void)
{
iocontext_cachep = kmem_cache_create("blkdev_ioc",
sizeof(struct io_context), 0, SLAB_PANIC, NULL);
return 0;
}
subsys_initcall(blk_ioc_init);
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