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![Jonathan Corbet](/assets/img/avatar_default.png)
Slow-work appears to delete its timer as soon as the first user unregisters, even though other users could be active. At the same time, it never seems to delete slow_work_oom_timer. Arrange for both to happen in the shutdown path. Signed-off-by: Jonathan Corbet <corbet@lwn.net> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
640 lines
18 KiB
C
640 lines
18 KiB
C
/* Worker thread pool for slow items, such as filesystem lookups or mkdirs
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*
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* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*
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* See Documentation/slow-work.txt
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*/
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#include <linux/module.h>
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#include <linux/slow-work.h>
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#include <linux/kthread.h>
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#include <linux/freezer.h>
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#include <linux/wait.h>
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#define SLOW_WORK_CULL_TIMEOUT (5 * HZ) /* cull threads 5s after running out of
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* things to do */
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#define SLOW_WORK_OOM_TIMEOUT (5 * HZ) /* can't start new threads for 5s after
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* OOM */
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static void slow_work_cull_timeout(unsigned long);
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static void slow_work_oom_timeout(unsigned long);
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#ifdef CONFIG_SYSCTL
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static int slow_work_min_threads_sysctl(struct ctl_table *, int, struct file *,
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void __user *, size_t *, loff_t *);
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static int slow_work_max_threads_sysctl(struct ctl_table *, int , struct file *,
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void __user *, size_t *, loff_t *);
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#endif
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/*
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* The pool of threads has at least min threads in it as long as someone is
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* using the facility, and may have as many as max.
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*
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* A portion of the pool may be processing very slow operations.
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*/
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static unsigned slow_work_min_threads = 2;
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static unsigned slow_work_max_threads = 4;
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static unsigned vslow_work_proportion = 50; /* % of threads that may process
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* very slow work */
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#ifdef CONFIG_SYSCTL
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static const int slow_work_min_min_threads = 2;
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static int slow_work_max_max_threads = 255;
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static const int slow_work_min_vslow = 1;
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static const int slow_work_max_vslow = 99;
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ctl_table slow_work_sysctls[] = {
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "min-threads",
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.data = &slow_work_min_threads,
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.maxlen = sizeof(unsigned),
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.mode = 0644,
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.proc_handler = slow_work_min_threads_sysctl,
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.extra1 = (void *) &slow_work_min_min_threads,
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.extra2 = &slow_work_max_threads,
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},
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "max-threads",
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.data = &slow_work_max_threads,
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.maxlen = sizeof(unsigned),
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.mode = 0644,
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.proc_handler = slow_work_max_threads_sysctl,
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.extra1 = &slow_work_min_threads,
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.extra2 = (void *) &slow_work_max_max_threads,
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},
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "vslow-percentage",
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.data = &vslow_work_proportion,
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.maxlen = sizeof(unsigned),
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.mode = 0644,
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.proc_handler = &proc_dointvec_minmax,
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.extra1 = (void *) &slow_work_min_vslow,
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.extra2 = (void *) &slow_work_max_vslow,
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},
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{ .ctl_name = 0 }
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};
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#endif
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/*
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* The active state of the thread pool
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*/
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static atomic_t slow_work_thread_count;
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static atomic_t vslow_work_executing_count;
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static bool slow_work_may_not_start_new_thread;
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static bool slow_work_cull; /* cull a thread due to lack of activity */
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static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
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static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
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static struct slow_work slow_work_new_thread; /* new thread starter */
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/*
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* The queues of work items and the lock governing access to them. These are
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* shared between all the CPUs. It doesn't make sense to have per-CPU queues
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* as the number of threads bears no relation to the number of CPUs.
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*
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* There are two queues of work items: one for slow work items, and one for
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* very slow work items.
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*/
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static LIST_HEAD(slow_work_queue);
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static LIST_HEAD(vslow_work_queue);
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static DEFINE_SPINLOCK(slow_work_queue_lock);
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/*
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* The thread controls. A variable used to signal to the threads that they
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* should exit when the queue is empty, a waitqueue used by the threads to wait
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* for signals, and a completion set by the last thread to exit.
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*/
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static bool slow_work_threads_should_exit;
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static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);
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static DECLARE_COMPLETION(slow_work_last_thread_exited);
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/*
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* The number of users of the thread pool and its lock. Whilst this is zero we
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* have no threads hanging around, and when this reaches zero, we wait for all
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* active or queued work items to complete and kill all the threads we do have.
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*/
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static int slow_work_user_count;
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static DEFINE_MUTEX(slow_work_user_lock);
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/*
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* Calculate the maximum number of active threads in the pool that are
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* permitted to process very slow work items.
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*
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* The answer is rounded up to at least 1, but may not equal or exceed the
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* maximum number of the threads in the pool. This means we always have at
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* least one thread that can process slow work items, and we always have at
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* least one thread that won't get tied up doing so.
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*/
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static unsigned slow_work_calc_vsmax(void)
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{
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unsigned vsmax;
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vsmax = atomic_read(&slow_work_thread_count) * vslow_work_proportion;
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vsmax /= 100;
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vsmax = max(vsmax, 1U);
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return min(vsmax, slow_work_max_threads - 1);
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}
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/*
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* Attempt to execute stuff queued on a slow thread. Return true if we managed
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* it, false if there was nothing to do.
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*/
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static bool slow_work_execute(void)
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{
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struct slow_work *work = NULL;
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unsigned vsmax;
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bool very_slow;
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vsmax = slow_work_calc_vsmax();
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/* see if we can schedule a new thread to be started if we're not
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* keeping up with the work */
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if (!waitqueue_active(&slow_work_thread_wq) &&
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(!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&
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atomic_read(&slow_work_thread_count) < slow_work_max_threads &&
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!slow_work_may_not_start_new_thread)
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slow_work_enqueue(&slow_work_new_thread);
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/* find something to execute */
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spin_lock_irq(&slow_work_queue_lock);
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if (!list_empty(&vslow_work_queue) &&
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atomic_read(&vslow_work_executing_count) < vsmax) {
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work = list_entry(vslow_work_queue.next,
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struct slow_work, link);
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if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
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BUG();
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list_del_init(&work->link);
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atomic_inc(&vslow_work_executing_count);
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very_slow = true;
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} else if (!list_empty(&slow_work_queue)) {
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work = list_entry(slow_work_queue.next,
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struct slow_work, link);
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if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
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BUG();
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list_del_init(&work->link);
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very_slow = false;
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} else {
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very_slow = false; /* avoid the compiler warning */
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}
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spin_unlock_irq(&slow_work_queue_lock);
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if (!work)
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return false;
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if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
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BUG();
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work->ops->execute(work);
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if (very_slow)
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atomic_dec(&vslow_work_executing_count);
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clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
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/* if someone tried to enqueue the item whilst we were executing it,
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* then it'll be left unenqueued to avoid multiple threads trying to
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* execute it simultaneously
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*
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* there is, however, a race between us testing the pending flag and
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* getting the spinlock, and between the enqueuer setting the pending
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* flag and getting the spinlock, so we use a deferral bit to tell us
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* if the enqueuer got there first
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*/
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if (test_bit(SLOW_WORK_PENDING, &work->flags)) {
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spin_lock_irq(&slow_work_queue_lock);
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if (!test_bit(SLOW_WORK_EXECUTING, &work->flags) &&
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test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags))
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goto auto_requeue;
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spin_unlock_irq(&slow_work_queue_lock);
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}
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work->ops->put_ref(work);
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return true;
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auto_requeue:
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/* we must complete the enqueue operation
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* - we transfer our ref on the item back to the appropriate queue
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* - don't wake another thread up as we're awake already
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*/
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if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
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list_add_tail(&work->link, &vslow_work_queue);
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else
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list_add_tail(&work->link, &slow_work_queue);
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spin_unlock_irq(&slow_work_queue_lock);
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return true;
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}
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/**
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* slow_work_enqueue - Schedule a slow work item for processing
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* @work: The work item to queue
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*
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* Schedule a slow work item for processing. If the item is already undergoing
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* execution, this guarantees not to re-enter the execution routine until the
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* first execution finishes.
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*
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* The item is pinned by this function as it retains a reference to it, managed
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* through the item operations. The item is unpinned once it has been
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* executed.
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*
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* An item may hog the thread that is running it for a relatively large amount
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* of time, sufficient, for example, to perform several lookup, mkdir, create
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* and setxattr operations. It may sleep on I/O and may sleep to obtain locks.
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*
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* Conversely, if a number of items are awaiting processing, it may take some
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* time before any given item is given attention. The number of threads in the
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* pool may be increased to deal with demand, but only up to a limit.
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*
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* If SLOW_WORK_VERY_SLOW is set on the work item, then it will be placed in
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* the very slow queue, from which only a portion of the threads will be
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* allowed to pick items to execute. This ensures that very slow items won't
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* overly block ones that are just ordinarily slow.
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*
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* Returns 0 if successful, -EAGAIN if not.
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*/
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int slow_work_enqueue(struct slow_work *work)
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{
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unsigned long flags;
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BUG_ON(slow_work_user_count <= 0);
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BUG_ON(!work);
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BUG_ON(!work->ops);
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BUG_ON(!work->ops->get_ref);
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/* when honouring an enqueue request, we only promise that we will run
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* the work function in the future; we do not promise to run it once
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* per enqueue request
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*
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* we use the PENDING bit to merge together repeat requests without
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* having to disable IRQs and take the spinlock, whilst still
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* maintaining our promise
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*/
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if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
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spin_lock_irqsave(&slow_work_queue_lock, flags);
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/* we promise that we will not attempt to execute the work
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* function in more than one thread simultaneously
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*
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* this, however, leaves us with a problem if we're asked to
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* enqueue the work whilst someone is executing the work
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* function as simply queueing the work immediately means that
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* another thread may try executing it whilst it is already
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* under execution
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*
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* to deal with this, we set the ENQ_DEFERRED bit instead of
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* enqueueing, and the thread currently executing the work
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* function will enqueue the work item when the work function
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* returns and it has cleared the EXECUTING bit
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*/
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if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
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set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
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} else {
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if (work->ops->get_ref(work) < 0)
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goto cant_get_ref;
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if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
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list_add_tail(&work->link, &vslow_work_queue);
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else
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list_add_tail(&work->link, &slow_work_queue);
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wake_up(&slow_work_thread_wq);
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}
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spin_unlock_irqrestore(&slow_work_queue_lock, flags);
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}
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return 0;
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cant_get_ref:
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spin_unlock_irqrestore(&slow_work_queue_lock, flags);
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return -EAGAIN;
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}
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EXPORT_SYMBOL(slow_work_enqueue);
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/*
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* Worker thread culling algorithm
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*/
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static bool slow_work_cull_thread(void)
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{
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unsigned long flags;
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bool do_cull = false;
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spin_lock_irqsave(&slow_work_queue_lock, flags);
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if (slow_work_cull) {
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slow_work_cull = false;
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if (list_empty(&slow_work_queue) &&
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list_empty(&vslow_work_queue) &&
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atomic_read(&slow_work_thread_count) >
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slow_work_min_threads) {
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mod_timer(&slow_work_cull_timer,
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jiffies + SLOW_WORK_CULL_TIMEOUT);
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do_cull = true;
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}
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}
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spin_unlock_irqrestore(&slow_work_queue_lock, flags);
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return do_cull;
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}
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/*
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* Determine if there is slow work available for dispatch
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*/
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static inline bool slow_work_available(int vsmax)
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{
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return !list_empty(&slow_work_queue) ||
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(!list_empty(&vslow_work_queue) &&
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atomic_read(&vslow_work_executing_count) < vsmax);
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}
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/*
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* Worker thread dispatcher
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*/
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static int slow_work_thread(void *_data)
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{
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int vsmax;
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DEFINE_WAIT(wait);
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set_freezable();
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set_user_nice(current, -5);
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for (;;) {
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vsmax = vslow_work_proportion;
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vsmax *= atomic_read(&slow_work_thread_count);
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vsmax /= 100;
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prepare_to_wait(&slow_work_thread_wq, &wait,
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TASK_INTERRUPTIBLE);
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if (!freezing(current) &&
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!slow_work_threads_should_exit &&
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!slow_work_available(vsmax) &&
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!slow_work_cull)
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schedule();
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finish_wait(&slow_work_thread_wq, &wait);
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try_to_freeze();
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vsmax = vslow_work_proportion;
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vsmax *= atomic_read(&slow_work_thread_count);
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vsmax /= 100;
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if (slow_work_available(vsmax) && slow_work_execute()) {
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cond_resched();
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if (list_empty(&slow_work_queue) &&
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list_empty(&vslow_work_queue) &&
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atomic_read(&slow_work_thread_count) >
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slow_work_min_threads)
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mod_timer(&slow_work_cull_timer,
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jiffies + SLOW_WORK_CULL_TIMEOUT);
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continue;
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}
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if (slow_work_threads_should_exit)
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break;
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if (slow_work_cull && slow_work_cull_thread())
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break;
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}
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if (atomic_dec_and_test(&slow_work_thread_count))
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complete_and_exit(&slow_work_last_thread_exited, 0);
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return 0;
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}
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/*
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* Handle thread cull timer expiration
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*/
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static void slow_work_cull_timeout(unsigned long data)
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{
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slow_work_cull = true;
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wake_up(&slow_work_thread_wq);
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}
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/*
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* Get a reference on slow work thread starter
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*/
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static int slow_work_new_thread_get_ref(struct slow_work *work)
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{
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return 0;
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}
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/*
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* Drop a reference on slow work thread starter
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*/
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static void slow_work_new_thread_put_ref(struct slow_work *work)
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{
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}
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/*
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* Start a new slow work thread
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*/
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static void slow_work_new_thread_execute(struct slow_work *work)
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{
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struct task_struct *p;
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if (slow_work_threads_should_exit)
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return;
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if (atomic_read(&slow_work_thread_count) >= slow_work_max_threads)
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return;
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if (!mutex_trylock(&slow_work_user_lock))
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return;
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slow_work_may_not_start_new_thread = true;
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atomic_inc(&slow_work_thread_count);
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p = kthread_run(slow_work_thread, NULL, "kslowd");
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if (IS_ERR(p)) {
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printk(KERN_DEBUG "Slow work thread pool: OOM\n");
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if (atomic_dec_and_test(&slow_work_thread_count))
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BUG(); /* we're running on a slow work thread... */
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mod_timer(&slow_work_oom_timer,
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jiffies + SLOW_WORK_OOM_TIMEOUT);
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} else {
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/* ratelimit the starting of new threads */
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mod_timer(&slow_work_oom_timer, jiffies + 1);
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}
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mutex_unlock(&slow_work_user_lock);
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}
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static const struct slow_work_ops slow_work_new_thread_ops = {
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.get_ref = slow_work_new_thread_get_ref,
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.put_ref = slow_work_new_thread_put_ref,
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.execute = slow_work_new_thread_execute,
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};
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/*
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* post-OOM new thread start suppression expiration
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*/
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static void slow_work_oom_timeout(unsigned long data)
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{
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slow_work_may_not_start_new_thread = false;
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}
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#ifdef CONFIG_SYSCTL
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/*
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* Handle adjustment of the minimum number of threads
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*/
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static int slow_work_min_threads_sysctl(struct ctl_table *table, int write,
|
|
struct file *filp, void __user *buffer,
|
|
size_t *lenp, loff_t *ppos)
|
|
{
|
|
int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
|
|
int n;
|
|
|
|
if (ret == 0) {
|
|
mutex_lock(&slow_work_user_lock);
|
|
if (slow_work_user_count > 0) {
|
|
/* see if we need to start or stop threads */
|
|
n = atomic_read(&slow_work_thread_count) -
|
|
slow_work_min_threads;
|
|
|
|
if (n < 0 && !slow_work_may_not_start_new_thread)
|
|
slow_work_enqueue(&slow_work_new_thread);
|
|
else if (n > 0)
|
|
mod_timer(&slow_work_cull_timer,
|
|
jiffies + SLOW_WORK_CULL_TIMEOUT);
|
|
}
|
|
mutex_unlock(&slow_work_user_lock);
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Handle adjustment of the maximum number of threads
|
|
*/
|
|
static int slow_work_max_threads_sysctl(struct ctl_table *table, int write,
|
|
struct file *filp, void __user *buffer,
|
|
size_t *lenp, loff_t *ppos)
|
|
{
|
|
int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
|
|
int n;
|
|
|
|
if (ret == 0) {
|
|
mutex_lock(&slow_work_user_lock);
|
|
if (slow_work_user_count > 0) {
|
|
/* see if we need to stop threads */
|
|
n = slow_work_max_threads -
|
|
atomic_read(&slow_work_thread_count);
|
|
|
|
if (n < 0)
|
|
mod_timer(&slow_work_cull_timer,
|
|
jiffies + SLOW_WORK_CULL_TIMEOUT);
|
|
}
|
|
mutex_unlock(&slow_work_user_lock);
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
#endif /* CONFIG_SYSCTL */
|
|
|
|
/**
|
|
* slow_work_register_user - Register a user of the facility
|
|
*
|
|
* Register a user of the facility, starting up the initial threads if there
|
|
* aren't any other users at this point. This will return 0 if successful, or
|
|
* an error if not.
|
|
*/
|
|
int slow_work_register_user(void)
|
|
{
|
|
struct task_struct *p;
|
|
int loop;
|
|
|
|
mutex_lock(&slow_work_user_lock);
|
|
|
|
if (slow_work_user_count == 0) {
|
|
printk(KERN_NOTICE "Slow work thread pool: Starting up\n");
|
|
init_completion(&slow_work_last_thread_exited);
|
|
|
|
slow_work_threads_should_exit = false;
|
|
slow_work_init(&slow_work_new_thread,
|
|
&slow_work_new_thread_ops);
|
|
slow_work_may_not_start_new_thread = false;
|
|
slow_work_cull = false;
|
|
|
|
/* start the minimum number of threads */
|
|
for (loop = 0; loop < slow_work_min_threads; loop++) {
|
|
atomic_inc(&slow_work_thread_count);
|
|
p = kthread_run(slow_work_thread, NULL, "kslowd");
|
|
if (IS_ERR(p))
|
|
goto error;
|
|
}
|
|
printk(KERN_NOTICE "Slow work thread pool: Ready\n");
|
|
}
|
|
|
|
slow_work_user_count++;
|
|
mutex_unlock(&slow_work_user_lock);
|
|
return 0;
|
|
|
|
error:
|
|
if (atomic_dec_and_test(&slow_work_thread_count))
|
|
complete(&slow_work_last_thread_exited);
|
|
if (loop > 0) {
|
|
printk(KERN_ERR "Slow work thread pool:"
|
|
" Aborting startup on ENOMEM\n");
|
|
slow_work_threads_should_exit = true;
|
|
wake_up_all(&slow_work_thread_wq);
|
|
wait_for_completion(&slow_work_last_thread_exited);
|
|
printk(KERN_ERR "Slow work thread pool: Aborted\n");
|
|
}
|
|
mutex_unlock(&slow_work_user_lock);
|
|
return PTR_ERR(p);
|
|
}
|
|
EXPORT_SYMBOL(slow_work_register_user);
|
|
|
|
/**
|
|
* slow_work_unregister_user - Unregister a user of the facility
|
|
*
|
|
* Unregister a user of the facility, killing all the threads if this was the
|
|
* last one.
|
|
*/
|
|
void slow_work_unregister_user(void)
|
|
{
|
|
mutex_lock(&slow_work_user_lock);
|
|
|
|
BUG_ON(slow_work_user_count <= 0);
|
|
|
|
slow_work_user_count--;
|
|
if (slow_work_user_count == 0) {
|
|
printk(KERN_NOTICE "Slow work thread pool: Shutting down\n");
|
|
slow_work_threads_should_exit = true;
|
|
del_timer_sync(&slow_work_cull_timer);
|
|
del_timer_sync(&slow_work_oom_timer);
|
|
wake_up_all(&slow_work_thread_wq);
|
|
wait_for_completion(&slow_work_last_thread_exited);
|
|
printk(KERN_NOTICE "Slow work thread pool:"
|
|
" Shut down complete\n");
|
|
}
|
|
|
|
mutex_unlock(&slow_work_user_lock);
|
|
}
|
|
EXPORT_SYMBOL(slow_work_unregister_user);
|
|
|
|
/*
|
|
* Initialise the slow work facility
|
|
*/
|
|
static int __init init_slow_work(void)
|
|
{
|
|
unsigned nr_cpus = num_possible_cpus();
|
|
|
|
if (slow_work_max_threads < nr_cpus)
|
|
slow_work_max_threads = nr_cpus;
|
|
#ifdef CONFIG_SYSCTL
|
|
if (slow_work_max_max_threads < nr_cpus * 2)
|
|
slow_work_max_max_threads = nr_cpus * 2;
|
|
#endif
|
|
return 0;
|
|
}
|
|
|
|
subsys_initcall(init_slow_work);
|