/*
* Copyright (C) 2007 Oracle. All rights reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* 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.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*/
#include <linux/kthread.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/freezer.h>
#include "async-thread.h"
#define WORK_QUEUED_BIT 0
#define WORK_DONE_BIT 1
#define WORK_ORDER_DONE_BIT 2
#define WORK_HIGH_PRIO_BIT 3
/*
* container for the kthread task pointer and the list of pending work
* One of these is allocated per thread.
*/
struct btrfs_worker_thread {
/* pool we belong to */
struct btrfs_workers *workers;
/* list of struct btrfs_work that are waiting for service */
struct list_head pending;
struct list_head prio_pending;
/* list of worker threads from struct btrfs_workers */
struct list_head worker_list;
/* kthread */
struct task_struct *task;
/* number of things on the pending list */
atomic_t num_pending;
/* reference counter for this struct */
atomic_t refs;
unsigned long sequence;
/* protects the pending list. */
spinlock_t lock;
/* set to non-zero when this thread is already awake and kicking */
int working;
/* are we currently idle */
int idle;
};
static int __btrfs_start_workers(struct btrfs_workers *workers);
/*
* btrfs_start_workers uses kthread_run, which can block waiting for memory
* for a very long time. It will actually throttle on page writeback,
* and so it may not make progress until after our btrfs worker threads
* process all of the pending work structs in their queue
*
* This means we can't use btrfs_start_workers from inside a btrfs worker
* thread that is used as part of cleaning dirty memory, which pretty much
* involves all of the worker threads.
*
* Instead we have a helper queue who never has more than one thread
* where we scheduler thread start operations. This worker_start struct
* is used to contain the work and hold a pointer to the queue that needs
* another worker.
*/
struct worker_start {
struct btrfs_work work;
struct btrfs_workers *queue;
};
static void start_new_worker_func(struct btrfs_work *work)
{
struct worker_start *start;
start = container_of(work, struct worker_start, work);
__btrfs_start_workers(start->queue);
kfree(start);
}
/*
* helper function to move a thread onto the idle list after it
* has finished some requests.
*/
static void check_idle_worker(struct btrfs_worker_thread *worker)
{
if (!worker->idle && atomic_read(&worker->num_pending) <
worker->workers->idle_thresh / 2) {
unsigned long flags;
spin_lock_irqsave(&worker->workers->lock, flags);
worker->idle = 1;
/* the list may be empty if the worker is just starting */
if (!list_empty(&worker->worker_list)) {
list_move(&worker->worker_list,
&worker->workers->idle_list);
}
spin_unlock_irqrestore(&worker->workers->lock, flags);
}
}
/*
* helper function to move a thread off the idle list after new
* pending work is added.
*/
static void check_busy_worker(struct btrfs_worker_thread *worker)
{
if (worker->idle && atomic_read(&worker->num_pending) >=
worker->workers->idle_thresh) {
unsigned long flags;
spin_lock_irqsave(&worker->workers->lock, flags);
worker->idle = 0;
if (!list_empty(&worker->worker_list)) {
list_move_tail(&worker->worker_list,
&worker->workers->worker_list);
}
spin_unlock_irqrestore(&worker->workers->lock, flags);
}
}
static void check_pending_worker_creates(struct btrfs_worker_thread *worker)
{
struct btrfs_workers *workers = worker->workers;
struct worker_start *start;
unsigned long flags;
rmb();
if (!workers->atomic_start_pending)
return;
start = kzalloc(sizeof(*start), GFP_NOFS);
if (!start)
return;
start->work.func = start_new_worker_func;
start->queue = workers;
spin_lock_irqsave(&workers->lock, flags);
if (!workers->atomic_start_pending)
goto out;
workers->atomic_start_pending = 0;
if (workers->num_workers + workers->num_workers_starting >=
workers->max_workers)
goto out;
workers->num_workers_starting += 1;
spin_unlock_irqrestore(&workers->lock, flags);
btrfs_queue_worker(workers->atomic_worker_start, &start->work);
return;
out:
kfree(start);
spin_unlock_irqrestore(&workers->lock, flags);
}
static noinline void run_ordered_completions(struct btrfs_workers *workers,
struct btrfs_work *work)
{
if (!workers->ordered)
return;
set_bit(WORK_DONE_BIT, &work->flags);
spin_lock(&workers->order_lock);
while (1) {
if (!list_empty(&workers->prio_order_list)) {
work = list_entry(workers->prio_order_list.next,
struct btrfs_work, order_list);
} else if (!list_empty(&workers->order_list)) {
work = list_entry(workers->order_list.next,
struct btrfs_work, order_list);
} else {
break;
}
if (!test_bit(WORK_DONE_BIT, &work->flags))
break;
/* we are going to call the ordered done function, but
* we leave the work item on the list as a barrier so
* that later work items that are done don't have their
* functions called before this one returns
*/
if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
break;
spin_unlock(&workers->order_lock);
work->ordered_func(work);
/* now take the lock again and drop our item from the list */
spin_lock(&workers->order_lock);
list_del(&work->order_list);
spin_unlock(&workers->order_lock);
/*
* we don't want to call the ordered free functions
* with the lock held though
*/
work->ordered_free(work);
spin_lock(&workers->order_lock);
}
spin_unlock(&workers->order_lock);
}
static void put_worker(struct btrfs_worker_thread *worker)
{
if (atomic_dec_and_test(&worker->refs))
kfree(worker);
}
static int try_worker_shutdown(struct btrfs_worker_thread *worker)
{
int freeit = 0;
spin_lock_irq(&worker->lock);
spin_lock(&worker->workers->lock);
if (worker->workers->num_workers > 1 &&
worker->idle &&
!worker->working &&
!list_empty(&worker->worker_list) &&
list_empty(&worker->prio_pending) &&
list_empty(&worker->pending) &&
atomic_read(&worker->num_pending) == 0) {
freeit = 1;
list_del_init(&worker->worker_list);
worker->workers->num_workers--;
}
spin_unlock(&worker->workers->lock);
spin_unlock_irq(&worker->lock);
if (freeit)
put_worker(worker);
return freeit;
}
static struct btrfs_work *get_next_work(struct btrfs_worker_thread *worker,
struct list_head *prio_head,
struct list_head *head)
{
struct btrfs_work *work = NULL;
struct list_head *cur = NULL;
if(!list_empty(prio_head))
cur = prio_head->next;
smp_mb();
if (!list_empty(&worker->prio_pending))
goto refill;
if (!list_empty(head))
cur = head->next;
if (cur)
goto out;
refill:
spin_lock_irq(&worker->lock);
list_splice_tail_init(&worker->prio_pending, prio_head);
list_splice_tail_init(&worker->pending, head);
if (!list_empty(prio_head))
cur = prio_head->next;
else if (!list_empty(head))
cur = head->next;
spin_unlock_irq(&worker->lock);
if (!cur)
goto out_fail;
out:
work = list_entry(cur, struct btrfs_work, list);
out_fail:
return work;
}
/*
* main loop for servicing work items
*/
static int worker_loop(void *arg)
{
struct btrfs_worker_thread *worker = arg;
struct list_head head;
struct list_head prio_head;
struct btrfs_work *work;
INIT_LIST_HEAD(&head);
INIT_LIST_HEAD(&prio_head);
do {
again:
while (1) {
work = get_next_work(worker, &prio_head, &head);
if (!work)
break;
list_del(&work->list);
clear_bit(WORK_QUEUED_BIT, &work->flags);
work->worker = worker;
work->func(work);
atomic_dec(&worker->num_pending);
/*
* unless this is an ordered work queue,
* 'work' was probably freed by func above.
*/
run_ordered_completions(worker->workers, work);
check_pending_worker_creates(worker);
cond_resched();
}
spin_lock_irq(&worker->lock);
check_idle_worker(worker);
if (freezing(current)) {
worker->working = 0;
spin_unlock_irq(&worker->lock);
try_to_freeze();
} else {
spin_unlock_irq(&worker->lock);
if (!kthread_should_stop()) {
cpu_relax();
/*
* we've dropped the lock, did someone else
* jump_in?
*/
smp_mb();
if (!list_empty(&worker->pending) ||
!list_empty(&worker->prio_pending))
continue;
/*
* this short schedule allows more work to
* come in without the queue functions
* needing to go through wake_up_process()
*
* worker->working is still 1, so nobody
* is going to try and wake us up
*/
schedule_timeout(1);
smp_mb();
if (!list_empty(&worker->pending) ||
!list_empty(&worker->prio_pending))
continue;
if (kthread_should_stop())
break;
/* still no more work?, sleep for real */
spin_lock_irq(&worker->lock);
set_current_state(TASK_INTERRUPTIBLE);
if (!list_empty(&worker->pending) ||
!list_empty(&worker->prio_pending)) {
spin_unlock_irq(&worker->lock);
set_current_state(TASK_RUNNING);
goto again;
}
/*
* this makes sure we get a wakeup when someone
* adds something new to the queue
*/
worker->working = 0;
spin_unlock_irq(&worker->lock);
if (!kthread_should_stop()) {
schedule_timeout(HZ * 120);
if (!worker->working &&
try_worker_shutdown(worker)) {
return 0;
}
}
}
__set_current_state(TASK_RUNNING);
}
} while (!kthread_should_stop());
return 0;
}
/*
* this will wait for all the worker threads to shutdown
*/
void btrfs_stop_workers(struct btrfs_workers *workers)
{
struct list_head *cur;
struct btrfs_worker_thread *worker;
int can_stop;
spin_lock_irq(&workers->lock);
list_splice_init(&workers->idle_list, &workers->worker_list);
while (!list_empty(&workers->worker_list)) {
cur = workers->worker_list.next;
worker = list_entry(cur, struct btrfs_worker_thread,
worker_list);
atomic_inc(&worker->refs);
workers->num_workers -= 1;
if (!list_empty(&worker->worker_list)) {
list_del_init(&worker->worker_list);
put_worker(worker);
can_stop = 1;
} else
can_stop = 0;
spin_unlock_irq(&workers->lock);
if (can_stop)
kthread_stop(worker->task);
spin_lock_irq(&workers->lock);
put_worker(worker);
}
spin_unlock_irq(&workers->lock);
}
/*
* simple init on struct btrfs_workers
*/
void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max,
struct btrfs_workers *async_helper)
{
workers->num_workers = 0;
workers->num_workers_starting = 0;
INIT_LIST_HEAD(&workers->worker_list);
INIT_LIST_HEAD(&workers->idle_list);
INIT_LIST_HEAD(&workers->order_list);
INIT_LIST_HEAD(&workers->prio_order_list);
spin_lock_init(&workers->lock);
spin_lock_init(&workers->order_lock);
workers->max_workers = max;
workers->idle_thresh = 32;
workers->name = name;
workers->ordered = 0;
workers->atomic_start_pending = 0;
workers->atomic_worker_start = async_helper;
}
/*
* starts new worker threads. This does not enforce the max worker
* count in case you need to temporarily go past it.
*/
static int __btrfs_start_workers(struct btrfs_workers *workers)
{
struct btrfs_worker_thread *worker;
int ret = 0;
worker = kzalloc(sizeof(*worker), GFP_NOFS);
if (!worker) {
ret = -ENOMEM;
goto fail;
}
INIT_LIST_HEAD(&worker->pending);
INIT_LIST_HEAD(&worker->prio_pending);
INIT_LIST_HEAD(&worker->worker_list);
spin_lock_init(&worker->lock);
atomic_set(&worker->num_pending, 0);
atomic_set(&worker->refs, 1);
worker->workers = workers;
worker->task = kthread_run(worker_loop, worker,
"btrfs-%s-%d", workers->name,
workers->num_workers + 1);
if (IS_ERR(worker->task)) {
ret = PTR_ERR(worker->task);
kfree(worker);
goto fail;
}
spin_lock_irq(&workers->lock);
list_add_tail(&worker->worker_list, &workers->idle_list);
worker->idle = 1;
workers->num_workers++;
workers->num_workers_starting--;
WARN_ON(workers->num_workers_starting < 0);
spin_unlock_irq(&workers->lock);
return 0;
fail:
spin_lock_irq(&workers->lock);
workers->num_workers_starting--;
spin_unlock_irq(&workers->lock);
return ret;
}
int btrfs_start_workers(struct btrfs_workers *workers)
{
spin_lock_irq(&workers->lock);
workers->num_workers_starting++;
spin_unlock_irq(&workers->lock);
return __btrfs_start_workers(workers);
}
/*
* run through the list and find a worker thread that doesn't have a lot
* to do right now. This can return null if we aren't yet at the thread
* count limit and all of the threads are busy.
*/
static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
{
struct btrfs_worker_thread *worker;
struct list_head *next;
int enforce_min;
enforce_min = (workers->num_workers + workers->num_workers_starting) <
workers->max_workers;
/*
* if we find an idle thread, don't move it to the end of the
* idle list. This improves the chance that the next submission
* will reuse the same thread, and maybe catch it while it is still
* working
*/
if (!list_empty(&workers->idle_list)) {
next = workers->idle_list.next;
worker = list_entry(next, struct btrfs_worker_thread,
worker_list);
return worker;
}
if (enforce_min || list_empty(&workers->worker_list))
return NULL;
/*
* if we pick a busy task, move the task to the end of the list.
* hopefully this will keep things somewhat evenly balanced.
* Do the move in batches based on the sequence number. This groups
* requests submitted at roughly the same time onto the same worker.
*/
next = workers->worker_list.next;
worker = list_entry(next, struct btrfs_worker_thread, worker_list);
worker->sequence++;
if (worker->sequence % workers->idle_thresh == 0)
list_move_tail(next, &workers->worker_list);
return worker;
}
/*
* selects a worker thread to take the next job. This will either find
* an idle worker, start a new worker up to the max count, or just return
* one of the existing busy workers.
*/
static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
{
struct btrfs_worker_thread *worker;
unsigned long flags;
struct list_head *fallback;
int ret;
spin_lock_irqsave(&workers->lock, flags);
again:
worker = next_worker(workers);
if (!worker) {
if (workers->num_workers + workers->num_workers_starting >=
workers->max_workers) {
goto fallback;
} else if (workers->atomic_worker_start) {
workers->atomic_start_pending = 1;
goto fallback;
} else {
workers->num_workers_starting++;
spin_unlock_irqrestore(&workers->lock, flags);
/* we're below the limit, start another worker */
ret = __btrfs_start_workers(workers);
spin_lock_irqsave(&workers->lock, flags);
if (ret)
goto fallback;
goto again;
}
}
goto found;
fallback:
fallback = NULL;
/*
* we have failed to find any workers, just
* return the first one we can find.
*/
if (!list_empty(&workers->worker_list))
fallback = workers->worker_list.next;
if (!list_empty(&workers->idle_list))
fallback = workers->idle_list.next;
BUG_ON(!fallback);
worker = list_entry(fallback,
struct btrfs_worker_thread, worker_list);
found:
/*
* this makes sure the worker doesn't exit before it is placed
* onto a busy/idle list
*/
atomic_inc(&worker->num_pending);
spin_unlock_irqrestore(&workers->lock, flags);
return worker;
}
/*
* btrfs_requeue_work just puts the work item back on the tail of the list
* it was taken from. It is intended for use with long running work functions
* that make some progress and want to give the cpu up for others.
*/
void btrfs_requeue_work(struct btrfs_work *work)
{
struct btrfs_worker_thread *worker = work->worker;
unsigned long flags;
int wake = 0;
if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
return;
spin_lock_irqsave(&worker->lock, flags);
if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
list_add_tail(&work->list, &worker->prio_pending);
else
list_add_tail(&work->list, &worker->pending);
atomic_inc(&worker->num_pending);
/* by definition we're busy, take ourselves off the idle
* list
*/
if (worker->idle) {
spin_lock(&worker->workers->lock);
worker->idle = 0;
list_move_tail(&worker->worker_list,
&worker->workers->worker_list);
spin_unlock(&worker->workers->lock);
}
if (!worker->working) {
wake = 1;
worker->working = 1;
}
if (wake)
wake_up_process(worker->task);
spin_unlock_irqrestore(&worker->lock, flags);
}
void btrfs_set_work_high_prio(struct btrfs_work *work)
{
set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
}
/*
* places a struct btrfs_work into the pending queue of one of the kthreads
*/
void btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
{
struct btrfs_worker_thread *worker;
unsigned long flags;
int wake = 0;
/* don't requeue something already on a list */
if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
return;
worker = find_worker(workers);
if (workers->ordered) {
/*
* you're not allowed to do ordered queues from an
* interrupt handler
*/
spin_lock(&workers->order_lock);
if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
list_add_tail(&work->order_list,
&workers->prio_order_list);
} else {
list_add_tail(&work->order_list, &workers->order_list);
}
spin_unlock(&workers->order_lock);
} else {
INIT_LIST_HEAD(&work->order_list);
}
spin_lock_irqsave(&worker->lock, flags);
if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
list_add_tail(&work->list, &worker->prio_pending);
else
list_add_tail(&work->list, &worker->pending);
check_busy_worker(worker);
/*
* avoid calling into wake_up_process if this thread has already
* been kicked
*/
if (!worker->working)
wake = 1;
worker->working = 1;
if (wake)
wake_up_process(worker->task);
spin_unlock_irqrestore(&worker->lock, flags);
}
