+++ /dev/null
- ====================================
- SLOW WORK ITEM EXECUTION THREAD POOL
- ====================================
-
-By: David Howells <dhowells@redhat.com>
-
-The slow work item execution thread pool is a pool of threads for performing
-things that take a relatively long time, such as making mkdir calls.
-Typically, when processing something, these items will spend a lot of time
-blocking a thread on I/O, thus making that thread unavailable for doing other
-work.
-
-The standard workqueue model is unsuitable for this class of work item as that
-limits the owner to a single thread or a single thread per CPU. For some
-tasks, however, more threads - or fewer - are required.
-
-There is just one pool per system. It contains no threads unless something
-wants to use it - and that something must register its interest first. When
-the pool is active, the number of threads it contains is dynamic, varying
-between a maximum and minimum setting, depending on the load.
-
-
-====================
-CLASSES OF WORK ITEM
-====================
-
-This pool support two classes of work items:
-
- (*) Slow work items.
-
- (*) Very slow work items.
-
-The former are expected to finish much quicker than the latter.
-
-An operation of the very slow class may do a batch combination of several
-lookups, mkdirs, and a create for instance.
-
-An operation of the ordinarily slow class may, for example, write stuff or
-expand files, provided the time taken to do so isn't too long.
-
-Operations of both types may sleep during execution, thus tying up the thread
-loaned to it.
-
-A further class of work item is available, based on the slow work item class:
-
- (*) Delayed slow work items.
-
-These are slow work items that have a timer to defer queueing of the item for
-a while.
-
-
-THREAD-TO-CLASS ALLOCATION
---------------------------
-
-Not all the threads in the pool are available to work on very slow work items.
-The number will be between one and one fewer than the number of active threads.
-This is configurable (see the "Pool Configuration" section).
-
-All the threads are available to work on ordinarily slow work items, but a
-percentage of the threads will prefer to work on very slow work items.
-
-The configuration ensures that at least one thread will be available to work on
-very slow work items, and at least one thread will be available that won't work
-on very slow work items at all.
-
-
-=====================
-USING SLOW WORK ITEMS
-=====================
-
-Firstly, a module or subsystem wanting to make use of slow work items must
-register its interest:
-
- int ret = slow_work_register_user(struct module *module);
-
-This will return 0 if successful, or a -ve error upon failure. The module
-pointer should be the module interested in using this facility (almost
-certainly THIS_MODULE).
-
-
-Slow work items may then be set up by:
-
- (1) Declaring a slow_work struct type variable:
-
- #include <linux/slow-work.h>
-
- struct slow_work myitem;
-
- (2) Declaring the operations to be used for this item:
-
- struct slow_work_ops myitem_ops = {
- .get_ref = myitem_get_ref,
- .put_ref = myitem_put_ref,
- .execute = myitem_execute,
- };
-
- [*] For a description of the ops, see section "Item Operations".
-
- (3) Initialising the item:
-
- slow_work_init(&myitem, &myitem_ops);
-
- or:
-
- delayed_slow_work_init(&myitem, &myitem_ops);
-
- or:
-
- vslow_work_init(&myitem, &myitem_ops);
-
- depending on its class.
-
-A suitably set up work item can then be enqueued for processing:
-
- int ret = slow_work_enqueue(&myitem);
-
-This will return a -ve error if the thread pool is unable to gain a reference
-on the item, 0 otherwise, or (for delayed work):
-
- int ret = delayed_slow_work_enqueue(&myitem, my_jiffy_delay);
-
-
-The items are reference counted, so there ought to be no need for a flush
-operation. But as the reference counting is optional, means to cancel
-existing work items are also included:
-
- cancel_slow_work(&myitem);
- cancel_delayed_slow_work(&myitem);
-
-can be used to cancel pending work. The above cancel function waits for
-existing work to have been executed (or prevent execution of them, depending
-on timing).
-
-
-When all a module's slow work items have been processed, and the
-module has no further interest in the facility, it should unregister its
-interest:
-
- slow_work_unregister_user(struct module *module);
-
-The module pointer is used to wait for all outstanding work items for that
-module before completing the unregistration. This prevents the put_ref() code
-from being taken away before it completes. module should almost certainly be
-THIS_MODULE.
-
-
-================
-HELPER FUNCTIONS
-================
-
-The slow-work facility provides a function by which it can be determined
-whether or not an item is queued for later execution:
-
- bool queued = slow_work_is_queued(struct slow_work *work);
-
-If it returns false, then the item is not on the queue (it may be executing
-with a requeue pending). This can be used to work out whether an item on which
-another depends is on the queue, thus allowing a dependent item to be queued
-after it.
-
-If the above shows an item on which another depends not to be queued, then the
-owner of the dependent item might need to wait. However, to avoid locking up
-the threads unnecessarily be sleeping in them, it can make sense under some
-circumstances to return the work item to the queue, thus deferring it until
-some other items have had a chance to make use of the yielded thread.
-
-To yield a thread and defer an item, the work function should simply enqueue
-the work item again and return. However, this doesn't work if there's nothing
-actually on the queue, as the thread just vacated will jump straight back into
-the item's work function, thus busy waiting on a CPU.
-
-Instead, the item should use the thread to wait for the dependency to go away,
-but rather than using schedule() or schedule_timeout() to sleep, it should use
-the following function:
-
- bool requeue = slow_work_sleep_till_thread_needed(
- struct slow_work *work,
- signed long *_timeout);
-
-This will add a second wait and then sleep, such that it will be woken up if
-either something appears on the queue that could usefully make use of the
-thread - and behind which this item can be queued, or if the event the caller
-set up to wait for happens. True will be returned if something else appeared
-on the queue and this work function should perhaps return, of false if
-something else woke it up. The timeout is as for schedule_timeout().
-
-For example:
-
- wq = bit_waitqueue(&my_flags, MY_BIT);
- init_wait(&wait);
- requeue = false;
- do {
- prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
- if (!test_bit(MY_BIT, &my_flags))
- break;
- requeue = slow_work_sleep_till_thread_needed(&my_work,
- &timeout);
- } while (timeout > 0 && !requeue);
- finish_wait(wq, &wait);
- if (!test_bit(MY_BIT, &my_flags)
- goto do_my_thing;
- if (requeue)
- return; // to slow_work
-
-
-===============
-ITEM OPERATIONS
-===============
-
-Each work item requires a table of operations of type struct slow_work_ops.
-Only ->execute() is required; the getting and putting of a reference and the
-describing of an item are all optional.
-
- (*) Get a reference on an item:
-
- int (*get_ref)(struct slow_work *work);
-
- This allows the thread pool to attempt to pin an item by getting a
- reference on it. This function should return 0 if the reference was
- granted, or a -ve error otherwise. If an error is returned,
- slow_work_enqueue() will fail.
-
- The reference is held whilst the item is queued and whilst it is being
- executed. The item may then be requeued with the same reference held, or
- the reference will be released.
-
- (*) Release a reference on an item:
-
- void (*put_ref)(struct slow_work *work);
-
- This allows the thread pool to unpin an item by releasing the reference on
- it. The thread pool will not touch the item again once this has been
- called.
-
- (*) Execute an item:
-
- void (*execute)(struct slow_work *work);
-
- This should perform the work required of the item. It may sleep, it may
- perform disk I/O and it may wait for locks.
-
- (*) View an item through /proc:
-
- void (*desc)(struct slow_work *work, struct seq_file *m);
-
- If supplied, this should print to 'm' a small string describing the work
- the item is to do. This should be no more than about 40 characters, and
- shouldn't include a newline character.
-
- See the 'Viewing executing and queued items' section below.
-
-
-==================
-POOL CONFIGURATION
-==================
-
-The slow-work thread pool has a number of configurables:
-
- (*) /proc/sys/kernel/slow-work/min-threads
-
- The minimum number of threads that should be in the pool whilst it is in
- use. This may be anywhere between 2 and max-threads.
-
- (*) /proc/sys/kernel/slow-work/max-threads
-
- The maximum number of threads that should in the pool. This may be
- anywhere between min-threads and 255 or NR_CPUS * 2, whichever is greater.
-
- (*) /proc/sys/kernel/slow-work/vslow-percentage
-
- The percentage of active threads in the pool that may be used to execute
- very slow work items. This may be between 1 and 99. The resultant number
- is bounded to between 1 and one fewer than the number of active threads.
- This ensures there is always at least one thread that can process very
- slow work items, and always at least one thread that won't.
-
-
-==================================
-VIEWING EXECUTING AND QUEUED ITEMS
-==================================
-
-If CONFIG_SLOW_WORK_DEBUG is enabled, a debugfs file is made available:
-
- /sys/kernel/debug/slow_work/runqueue
-
-through which the list of work items being executed and the queues of items to
-be executed may be viewed. The owner of a work item is given the chance to
-add some information of its own.
-
-The contents look something like the following:
-
- THR PID ITEM ADDR FL MARK DESC
- === ===== ================ == ===== ==========
- 0 3005 ffff880023f52348 a 952ms FSC: OBJ17d3: LOOK
- 1 3006 ffff880024e33668 2 160ms FSC: OBJ17e5 OP60d3b: Write1/Store fl=2
- 2 3165 ffff8800296dd180 a 424ms FSC: OBJ17e4: LOOK
- 3 4089 ffff8800262c8d78 a 212ms FSC: OBJ17ea: CRTN
- 4 4090 ffff88002792bed8 2 388ms FSC: OBJ17e8 OP60d36: Write1/Store fl=2
- 5 4092 ffff88002a0ef308 2 388ms FSC: OBJ17e7 OP60d2e: Write1/Store fl=2
- 6 4094 ffff88002abaf4b8 2 132ms FSC: OBJ17e2 OP60d4e: Write1/Store fl=2
- 7 4095 ffff88002bb188e0 a 388ms FSC: OBJ17e9: CRTN
- vsq - ffff880023d99668 1 308ms FSC: OBJ17e0 OP60f91: Write1/EnQ fl=2
- vsq - ffff8800295d1740 1 212ms FSC: OBJ16be OP4d4b6: Write1/EnQ fl=2
- vsq - ffff880025ba3308 1 160ms FSC: OBJ179a OP58dec: Write1/EnQ fl=2
- vsq - ffff880024ec83e0 1 160ms FSC: OBJ17ae OP599f2: Write1/EnQ fl=2
- vsq - ffff880026618e00 1 160ms FSC: OBJ17e6 OP60d33: Write1/EnQ fl=2
- vsq - ffff880025a2a4b8 1 132ms FSC: OBJ16a2 OP4d583: Write1/EnQ fl=2
- vsq - ffff880023cbe6d8 9 212ms FSC: OBJ17eb: LOOK
- vsq - ffff880024d37590 9 212ms FSC: OBJ17ec: LOOK
- vsq - ffff880027746cb0 9 212ms FSC: OBJ17ed: LOOK
- vsq - ffff880024d37ae8 9 212ms FSC: OBJ17ee: LOOK
- vsq - ffff880024d37cb0 9 212ms FSC: OBJ17ef: LOOK
- vsq - ffff880025036550 9 212ms FSC: OBJ17f0: LOOK
- vsq - ffff8800250368e0 9 212ms FSC: OBJ17f1: LOOK
- vsq - ffff880025036aa8 9 212ms FSC: OBJ17f2: LOOK
-
-In the 'THR' column, executing items show the thread they're occupying and
-queued threads indicate which queue they're on. 'PID' shows the process ID of
-a slow-work thread that's executing something. 'FL' shows the work item flags.
-'MARK' indicates how long since an item was queued or began executing. Lastly,
-the 'DESC' column permits the owner of an item to give some information.
-
+++ /dev/null
-/* Worker thread pool for slow items, such as filesystem lookups or mkdirs
- *
- * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
- * Written by David Howells (dhowells@redhat.com)
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public Licence
- * as published by the Free Software Foundation; either version
- * 2 of the Licence, or (at your option) any later version.
- *
- * See Documentation/slow-work.txt
- */
-
-#include <linux/module.h>
-#include <linux/slow-work.h>
-#include <linux/kthread.h>
-#include <linux/freezer.h>
-#include <linux/wait.h>
-#include <linux/debugfs.h>
-#include "slow-work.h"
-
-static void slow_work_cull_timeout(unsigned long);
-static void slow_work_oom_timeout(unsigned long);
-
-#ifdef CONFIG_SYSCTL
-static int slow_work_min_threads_sysctl(struct ctl_table *, int,
- void __user *, size_t *, loff_t *);
-
-static int slow_work_max_threads_sysctl(struct ctl_table *, int ,
- void __user *, size_t *, loff_t *);
-#endif
-
-/*
- * The pool of threads has at least min threads in it as long as someone is
- * using the facility, and may have as many as max.
- *
- * A portion of the pool may be processing very slow operations.
- */
-static unsigned slow_work_min_threads = 2;
-static unsigned slow_work_max_threads = 4;
-static unsigned vslow_work_proportion = 50; /* % of threads that may process
- * very slow work */
-
-#ifdef CONFIG_SYSCTL
-static const int slow_work_min_min_threads = 2;
-static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT;
-static const int slow_work_min_vslow = 1;
-static const int slow_work_max_vslow = 99;
-
-ctl_table slow_work_sysctls[] = {
- {
- .procname = "min-threads",
- .data = &slow_work_min_threads,
- .maxlen = sizeof(unsigned),
- .mode = 0644,
- .proc_handler = slow_work_min_threads_sysctl,
- .extra1 = (void *) &slow_work_min_min_threads,
- .extra2 = &slow_work_max_threads,
- },
- {
- .procname = "max-threads",
- .data = &slow_work_max_threads,
- .maxlen = sizeof(unsigned),
- .mode = 0644,
- .proc_handler = slow_work_max_threads_sysctl,
- .extra1 = &slow_work_min_threads,
- .extra2 = (void *) &slow_work_max_max_threads,
- },
- {
- .procname = "vslow-percentage",
- .data = &vslow_work_proportion,
- .maxlen = sizeof(unsigned),
- .mode = 0644,
- .proc_handler = proc_dointvec_minmax,
- .extra1 = (void *) &slow_work_min_vslow,
- .extra2 = (void *) &slow_work_max_vslow,
- },
- {}
-};
-#endif
-
-/*
- * The active state of the thread pool
- */
-static atomic_t slow_work_thread_count;
-static atomic_t vslow_work_executing_count;
-
-static bool slow_work_may_not_start_new_thread;
-static bool slow_work_cull; /* cull a thread due to lack of activity */
-static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
-static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
-static struct slow_work slow_work_new_thread; /* new thread starter */
-
-/*
- * slow work ID allocation (use slow_work_queue_lock)
- */
-static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
-
-/*
- * Unregistration tracking to prevent put_ref() from disappearing during module
- * unload
- */
-#ifdef CONFIG_MODULES
-static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];
-static struct module *slow_work_unreg_module;
-static struct slow_work *slow_work_unreg_work_item;
-static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);
-static DEFINE_MUTEX(slow_work_unreg_sync_lock);
-
-static void slow_work_set_thread_processing(int id, struct slow_work *work)
-{
- if (work)
- slow_work_thread_processing[id] = work->owner;
-}
-static void slow_work_done_thread_processing(int id, struct slow_work *work)
-{
- struct module *module = slow_work_thread_processing[id];
-
- slow_work_thread_processing[id] = NULL;
- smp_mb();
- if (slow_work_unreg_work_item == work ||
- slow_work_unreg_module == module)
- wake_up_all(&slow_work_unreg_wq);
-}
-static void slow_work_clear_thread_processing(int id)
-{
- slow_work_thread_processing[id] = NULL;
-}
-#else
-static void slow_work_set_thread_processing(int id, struct slow_work *work) {}
-static void slow_work_done_thread_processing(int id, struct slow_work *work) {}
-static void slow_work_clear_thread_processing(int id) {}
-#endif
-
-/*
- * Data for tracking currently executing items for indication through /proc
- */
-#ifdef CONFIG_SLOW_WORK_DEBUG
-struct slow_work *slow_work_execs[SLOW_WORK_THREAD_LIMIT];
-pid_t slow_work_pids[SLOW_WORK_THREAD_LIMIT];
-DEFINE_RWLOCK(slow_work_execs_lock);
-#endif
-
-/*
- * The queues of work items and the lock governing access to them. These are
- * shared between all the CPUs. It doesn't make sense to have per-CPU queues
- * as the number of threads bears no relation to the number of CPUs.
- *
- * There are two queues of work items: one for slow work items, and one for
- * very slow work items.
- */
-LIST_HEAD(slow_work_queue);
-LIST_HEAD(vslow_work_queue);
-DEFINE_SPINLOCK(slow_work_queue_lock);
-
-/*
- * The following are two wait queues that get pinged when a work item is placed
- * on an empty queue. These allow work items that are hogging a thread by
- * sleeping in a way that could be deferred to yield their thread and enqueue
- * themselves.
- */
-static DECLARE_WAIT_QUEUE_HEAD(slow_work_queue_waits_for_occupation);
-static DECLARE_WAIT_QUEUE_HEAD(vslow_work_queue_waits_for_occupation);
-
-/*
- * The thread controls. A variable used to signal to the threads that they
- * should exit when the queue is empty, a waitqueue used by the threads to wait
- * for signals, and a completion set by the last thread to exit.
- */
-static bool slow_work_threads_should_exit;
-static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);
-static DECLARE_COMPLETION(slow_work_last_thread_exited);
-
-/*
- * The number of users of the thread pool and its lock. Whilst this is zero we
- * have no threads hanging around, and when this reaches zero, we wait for all
- * active or queued work items to complete and kill all the threads we do have.
- */
-static int slow_work_user_count;
-static DEFINE_MUTEX(slow_work_user_lock);
-
-static inline int slow_work_get_ref(struct slow_work *work)
-{
- if (work->ops->get_ref)
- return work->ops->get_ref(work);
-
- return 0;
-}
-
-static inline void slow_work_put_ref(struct slow_work *work)
-{
- if (work->ops->put_ref)
- work->ops->put_ref(work);
-}
-
-/*
- * Calculate the maximum number of active threads in the pool that are
- * permitted to process very slow work items.
- *
- * The answer is rounded up to at least 1, but may not equal or exceed the
- * maximum number of the threads in the pool. This means we always have at
- * least one thread that can process slow work items, and we always have at
- * least one thread that won't get tied up doing so.
- */
-static unsigned slow_work_calc_vsmax(void)
-{
- unsigned vsmax;
-
- vsmax = atomic_read(&slow_work_thread_count) * vslow_work_proportion;
- vsmax /= 100;
- vsmax = max(vsmax, 1U);
- return min(vsmax, slow_work_max_threads - 1);
-}
-
-/*
- * Attempt to execute stuff queued on a slow thread. Return true if we managed
- * it, false if there was nothing to do.
- */
-static noinline bool slow_work_execute(int id)
-{
- struct slow_work *work = NULL;
- unsigned vsmax;
- bool very_slow;
-
- vsmax = slow_work_calc_vsmax();
-
- /* see if we can schedule a new thread to be started if we're not
- * keeping up with the work */
- if (!waitqueue_active(&slow_work_thread_wq) &&
- (!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&
- atomic_read(&slow_work_thread_count) < slow_work_max_threads &&
- !slow_work_may_not_start_new_thread)
- slow_work_enqueue(&slow_work_new_thread);
-
- /* find something to execute */
- spin_lock_irq(&slow_work_queue_lock);
- if (!list_empty(&vslow_work_queue) &&
- atomic_read(&vslow_work_executing_count) < vsmax) {
- work = list_entry(vslow_work_queue.next,
- struct slow_work, link);
- if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
- BUG();
- list_del_init(&work->link);
- atomic_inc(&vslow_work_executing_count);
- very_slow = true;
- } else if (!list_empty(&slow_work_queue)) {
- work = list_entry(slow_work_queue.next,
- struct slow_work, link);
- if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
- BUG();
- list_del_init(&work->link);
- very_slow = false;
- } else {
- very_slow = false; /* avoid the compiler warning */
- }
-
- slow_work_set_thread_processing(id, work);
- if (work) {
- slow_work_mark_time(work);
- slow_work_begin_exec(id, work);
- }
-
- spin_unlock_irq(&slow_work_queue_lock);
-
- if (!work)
- return false;
-
- if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
- BUG();
-
- /* don't execute if the work is in the process of being cancelled */
- if (!test_bit(SLOW_WORK_CANCELLING, &work->flags))
- work->ops->execute(work);
-
- if (very_slow)
- atomic_dec(&vslow_work_executing_count);
- clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
-
- /* wake up anyone waiting for this work to be complete */
- wake_up_bit(&work->flags, SLOW_WORK_EXECUTING);
-
- slow_work_end_exec(id, work);
-
- /* if someone tried to enqueue the item whilst we were executing it,
- * then it'll be left unenqueued to avoid multiple threads trying to
- * execute it simultaneously
- *
- * there is, however, a race between us testing the pending flag and
- * getting the spinlock, and between the enqueuer setting the pending
- * flag and getting the spinlock, so we use a deferral bit to tell us
- * if the enqueuer got there first
- */
- if (test_bit(SLOW_WORK_PENDING, &work->flags)) {
- spin_lock_irq(&slow_work_queue_lock);
-
- if (!test_bit(SLOW_WORK_EXECUTING, &work->flags) &&
- test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags))
- goto auto_requeue;
-
- spin_unlock_irq(&slow_work_queue_lock);
- }
-
- /* sort out the race between module unloading and put_ref() */
- slow_work_put_ref(work);
- slow_work_done_thread_processing(id, work);
-
- return true;
-
-auto_requeue:
- /* we must complete the enqueue operation
- * - we transfer our ref on the item back to the appropriate queue
- * - don't wake another thread up as we're awake already
- */
- slow_work_mark_time(work);
- if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
- list_add_tail(&work->link, &vslow_work_queue);
- else
- list_add_tail(&work->link, &slow_work_queue);
- spin_unlock_irq(&slow_work_queue_lock);
- slow_work_clear_thread_processing(id);
- return true;
-}
-
-/**
- * slow_work_sleep_till_thread_needed - Sleep till thread needed by other work
- * work: The work item under execution that wants to sleep
- * _timeout: Scheduler sleep timeout
- *
- * Allow a requeueable work item to sleep on a slow-work processor thread until
- * that thread is needed to do some other work or the sleep is interrupted by
- * some other event.
- *
- * The caller must set up a wake up event before calling this and must have set
- * the appropriate sleep mode (such as TASK_UNINTERRUPTIBLE) and tested its own
- * condition before calling this function as no test is made here.
- *
- * False is returned if there is nothing on the queue; true is returned if the
- * work item should be requeued
- */
-bool slow_work_sleep_till_thread_needed(struct slow_work *work,
- signed long *_timeout)
-{
- wait_queue_head_t *wfo_wq;
- struct list_head *queue;
-
- DEFINE_WAIT(wait);
-
- if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
- wfo_wq = &vslow_work_queue_waits_for_occupation;
- queue = &vslow_work_queue;
- } else {
- wfo_wq = &slow_work_queue_waits_for_occupation;
- queue = &slow_work_queue;
- }
-
- if (!list_empty(queue))
- return true;
-
- add_wait_queue_exclusive(wfo_wq, &wait);
- if (list_empty(queue))
- *_timeout = schedule_timeout(*_timeout);
- finish_wait(wfo_wq, &wait);
-
- return !list_empty(queue);
-}
-EXPORT_SYMBOL(slow_work_sleep_till_thread_needed);
-
-/**
- * slow_work_enqueue - Schedule a slow work item for processing
- * @work: The work item to queue
- *
- * Schedule a slow work item for processing. If the item is already undergoing
- * execution, this guarantees not to re-enter the execution routine until the
- * first execution finishes.
- *
- * The item is pinned by this function as it retains a reference to it, managed
- * through the item operations. The item is unpinned once it has been
- * executed.
- *
- * An item may hog the thread that is running it for a relatively large amount
- * of time, sufficient, for example, to perform several lookup, mkdir, create
- * and setxattr operations. It may sleep on I/O and may sleep to obtain locks.
- *
- * Conversely, if a number of items are awaiting processing, it may take some
- * time before any given item is given attention. The number of threads in the
- * pool may be increased to deal with demand, but only up to a limit.
- *
- * If SLOW_WORK_VERY_SLOW is set on the work item, then it will be placed in
- * the very slow queue, from which only a portion of the threads will be
- * allowed to pick items to execute. This ensures that very slow items won't
- * overly block ones that are just ordinarily slow.
- *
- * Returns 0 if successful, -EAGAIN if not (or -ECANCELED if cancelled work is
- * attempted queued)
- */
-int slow_work_enqueue(struct slow_work *work)
-{
- wait_queue_head_t *wfo_wq;
- struct list_head *queue;
- unsigned long flags;
- int ret;
-
- if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
- return -ECANCELED;
-
- BUG_ON(slow_work_user_count <= 0);
- BUG_ON(!work);
- BUG_ON(!work->ops);
-
- /* when honouring an enqueue request, we only promise that we will run
- * the work function in the future; we do not promise to run it once
- * per enqueue request
- *
- * we use the PENDING bit to merge together repeat requests without
- * having to disable IRQs and take the spinlock, whilst still
- * maintaining our promise
- */
- if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
- if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
- wfo_wq = &vslow_work_queue_waits_for_occupation;
- queue = &vslow_work_queue;
- } else {
- wfo_wq = &slow_work_queue_waits_for_occupation;
- queue = &slow_work_queue;
- }
-
- spin_lock_irqsave(&slow_work_queue_lock, flags);
-
- if (unlikely(test_bit(SLOW_WORK_CANCELLING, &work->flags)))
- goto cancelled;
-
- /* we promise that we will not attempt to execute the work
- * function in more than one thread simultaneously
- *
- * this, however, leaves us with a problem if we're asked to
- * enqueue the work whilst someone is executing the work
- * function as simply queueing the work immediately means that
- * another thread may try executing it whilst it is already
- * under execution
- *
- * to deal with this, we set the ENQ_DEFERRED bit instead of
- * enqueueing, and the thread currently executing the work
- * function will enqueue the work item when the work function
- * returns and it has cleared the EXECUTING bit
- */
- if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
- set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
- } else {
- ret = slow_work_get_ref(work);
- if (ret < 0)
- goto failed;
- slow_work_mark_time(work);
- list_add_tail(&work->link, queue);
- wake_up(&slow_work_thread_wq);
-
- /* if someone who could be requeued is sleeping on a
- * thread, then ask them to yield their thread */
- if (work->link.prev == queue)
- wake_up(wfo_wq);
- }
-
- spin_unlock_irqrestore(&slow_work_queue_lock, flags);
- }
- return 0;
-
-cancelled:
- ret = -ECANCELED;
-failed:
- spin_unlock_irqrestore(&slow_work_queue_lock, flags);
- return ret;
-}
-EXPORT_SYMBOL(slow_work_enqueue);
-
-static int slow_work_wait(void *word)
-{
- schedule();
- return 0;
-}
-
-/**
- * slow_work_cancel - Cancel a slow work item
- * @work: The work item to cancel
- *
- * This function will cancel a previously enqueued work item. If we cannot
- * cancel the work item, it is guarenteed to have run when this function
- * returns.
- */
-void slow_work_cancel(struct slow_work *work)
-{
- bool wait = true, put = false;
-
- set_bit(SLOW_WORK_CANCELLING, &work->flags);
- smp_mb();
-
- /* if the work item is a delayed work item with an active timer, we
- * need to wait for the timer to finish _before_ getting the spinlock,
- * lest we deadlock against the timer routine
- *
- * the timer routine will leave DELAYED set if it notices the
- * CANCELLING flag in time
- */
- if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
- struct delayed_slow_work *dwork =
- container_of(work, struct delayed_slow_work, work);
- del_timer_sync(&dwork->timer);
- }
-
- spin_lock_irq(&slow_work_queue_lock);
-
- if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
- /* the timer routine aborted or never happened, so we are left
- * holding the timer's reference on the item and should just
- * drop the pending flag and wait for any ongoing execution to
- * finish */
- struct delayed_slow_work *dwork =
- container_of(work, struct delayed_slow_work, work);
-
- BUG_ON(timer_pending(&dwork->timer));
- BUG_ON(!list_empty(&work->link));
-
- clear_bit(SLOW_WORK_DELAYED, &work->flags);
- put = true;
- clear_bit(SLOW_WORK_PENDING, &work->flags);
-
- } else if (test_bit(SLOW_WORK_PENDING, &work->flags) &&
- !list_empty(&work->link)) {
- /* the link in the pending queue holds a reference on the item
- * that we will need to release */
- list_del_init(&work->link);
- wait = false;
- put = true;
- clear_bit(SLOW_WORK_PENDING, &work->flags);
-
- } else if (test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags)) {
- /* the executor is holding our only reference on the item, so
- * we merely need to wait for it to finish executing */
- clear_bit(SLOW_WORK_PENDING, &work->flags);
- }
-
- spin_unlock_irq(&slow_work_queue_lock);
-
- /* the EXECUTING flag is set by the executor whilst the spinlock is set
- * and before the item is dequeued - so assuming the above doesn't
- * actually dequeue it, simply waiting for the EXECUTING flag to be
- * released here should be sufficient */
- if (wait)
- wait_on_bit(&work->flags, SLOW_WORK_EXECUTING, slow_work_wait,
- TASK_UNINTERRUPTIBLE);
-
- clear_bit(SLOW_WORK_CANCELLING, &work->flags);
- if (put)
- slow_work_put_ref(work);
-}
-EXPORT_SYMBOL(slow_work_cancel);
-
-/*
- * Handle expiry of the delay timer, indicating that a delayed slow work item
- * should now be queued if not cancelled
- */
-static void delayed_slow_work_timer(unsigned long data)
-{
- wait_queue_head_t *wfo_wq;
- struct list_head *queue;
- struct slow_work *work = (struct slow_work *) data;
- unsigned long flags;
- bool queued = false, put = false, first = false;
-
- if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
- wfo_wq = &vslow_work_queue_waits_for_occupation;
- queue = &vslow_work_queue;
- } else {
- wfo_wq = &slow_work_queue_waits_for_occupation;
- queue = &slow_work_queue;
- }
-
- spin_lock_irqsave(&slow_work_queue_lock, flags);
- if (likely(!test_bit(SLOW_WORK_CANCELLING, &work->flags))) {
- clear_bit(SLOW_WORK_DELAYED, &work->flags);
-
- if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
- /* we discard the reference the timer was holding in
- * favour of the one the executor holds */
- set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
- put = true;
- } else {
- slow_work_mark_time(work);
- list_add_tail(&work->link, queue);
- queued = true;
- if (work->link.prev == queue)
- first = true;
- }
- }
-
- spin_unlock_irqrestore(&slow_work_queue_lock, flags);
- if (put)
- slow_work_put_ref(work);
- if (first)
- wake_up(wfo_wq);
- if (queued)
- wake_up(&slow_work_thread_wq);
-}
-
-/**
- * delayed_slow_work_enqueue - Schedule a delayed slow work item for processing
- * @dwork: The delayed work item to queue
- * @delay: When to start executing the work, in jiffies from now
- *
- * This is similar to slow_work_enqueue(), but it adds a delay before the work
- * is actually queued for processing.
- *
- * The item can have delayed processing requested on it whilst it is being
- * executed. The delay will begin immediately, and if it expires before the
- * item finishes executing, the item will be placed back on the queue when it
- * has done executing.
- */
-int delayed_slow_work_enqueue(struct delayed_slow_work *dwork,
- unsigned long delay)
-{
- struct slow_work *work = &dwork->work;
- unsigned long flags;
- int ret;
-
- if (delay == 0)
- return slow_work_enqueue(&dwork->work);
-
- BUG_ON(slow_work_user_count <= 0);
- BUG_ON(!work);
- BUG_ON(!work->ops);
-
- if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
- return -ECANCELED;
-
- if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
- spin_lock_irqsave(&slow_work_queue_lock, flags);
-
- if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
- goto cancelled;
-
- /* the timer holds a reference whilst it is pending */
- ret = slow_work_get_ref(work);
- if (ret < 0)
- goto cant_get_ref;
-
- if (test_and_set_bit(SLOW_WORK_DELAYED, &work->flags))
- BUG();
- dwork->timer.expires = jiffies + delay;
- dwork->timer.data = (unsigned long) work;
- dwork->timer.function = delayed_slow_work_timer;
- add_timer(&dwork->timer);
-
- spin_unlock_irqrestore(&slow_work_queue_lock, flags);
- }
-
- return 0;
-
-cancelled:
- ret = -ECANCELED;
-cant_get_ref:
- spin_unlock_irqrestore(&slow_work_queue_lock, flags);
- return ret;
-}
-EXPORT_SYMBOL(delayed_slow_work_enqueue);
-
-/*
- * Schedule a cull of the thread pool at some time in the near future
- */
-static void slow_work_schedule_cull(void)
-{
- mod_timer(&slow_work_cull_timer,
- round_jiffies(jiffies + SLOW_WORK_CULL_TIMEOUT));
-}
-
-/*
- * Worker thread culling algorithm
- */
-static bool slow_work_cull_thread(void)
-{
- unsigned long flags;
- bool do_cull = false;
-
- spin_lock_irqsave(&slow_work_queue_lock, flags);
-
- if (slow_work_cull) {
- slow_work_cull = false;
-
- if (list_empty(&slow_work_queue) &&
- list_empty(&vslow_work_queue) &&
- atomic_read(&slow_work_thread_count) >
- slow_work_min_threads) {
- slow_work_schedule_cull();
- do_cull = true;
- }
- }
-
- spin_unlock_irqrestore(&slow_work_queue_lock, flags);
- return do_cull;
-}
-
-/*
- * Determine if there is slow work available for dispatch
- */
-static inline bool slow_work_available(int vsmax)
-{
- return !list_empty(&slow_work_queue) ||
- (!list_empty(&vslow_work_queue) &&
- atomic_read(&vslow_work_executing_count) < vsmax);
-}
-
-/*
- * Worker thread dispatcher
- */
-static int slow_work_thread(void *_data)
-{
- int vsmax, id;
-
- DEFINE_WAIT(wait);
-
- set_freezable();
- set_user_nice(current, -5);
-
- /* allocate ourselves an ID */
- spin_lock_irq(&slow_work_queue_lock);
- id = find_first_zero_bit(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
- BUG_ON(id < 0 || id >= SLOW_WORK_THREAD_LIMIT);
- __set_bit(id, slow_work_ids);
- slow_work_set_thread_pid(id, current->pid);
- spin_unlock_irq(&slow_work_queue_lock);
-
- sprintf(current->comm, "kslowd%03u", id);
-
- for (;;) {
- vsmax = vslow_work_proportion;
- vsmax *= atomic_read(&slow_work_thread_count);
- vsmax /= 100;
-
- prepare_to_wait_exclusive(&slow_work_thread_wq, &wait,
- TASK_INTERRUPTIBLE);
- if (!freezing(current) &&
- !slow_work_threads_should_exit &&
- !slow_work_available(vsmax) &&
- !slow_work_cull)
- schedule();
- finish_wait(&slow_work_thread_wq, &wait);
-
- try_to_freeze();
-
- vsmax = vslow_work_proportion;
- vsmax *= atomic_read(&slow_work_thread_count);
- vsmax /= 100;
-
- if (slow_work_available(vsmax) && slow_work_execute(id)) {
- cond_resched();
- if (list_empty(&slow_work_queue) &&
- list_empty(&vslow_work_queue) &&
- atomic_read(&slow_work_thread_count) >
- slow_work_min_threads)
- slow_work_schedule_cull();
- continue;
- }
-
- if (slow_work_threads_should_exit)
- break;
-
- if (slow_work_cull && slow_work_cull_thread())
- break;
- }
-
- spin_lock_irq(&slow_work_queue_lock);
- slow_work_set_thread_pid(id, 0);
- __clear_bit(id, slow_work_ids);
- spin_unlock_irq(&slow_work_queue_lock);
-
- if (atomic_dec_and_test(&slow_work_thread_count))
- complete_and_exit(&slow_work_last_thread_exited, 0);
- return 0;
-}
-
-/*
- * Handle thread cull timer expiration
- */
-static void slow_work_cull_timeout(unsigned long data)
-{
- slow_work_cull = true;
- wake_up(&slow_work_thread_wq);
-}
-
-/*
- * Start a new slow work thread
- */
-static void slow_work_new_thread_execute(struct slow_work *work)
-{
- struct task_struct *p;
-
- if (slow_work_threads_should_exit)
- return;
-
- if (atomic_read(&slow_work_thread_count) >= slow_work_max_threads)
- return;
-
- if (!mutex_trylock(&slow_work_user_lock))
- return;
-
- slow_work_may_not_start_new_thread = true;
- atomic_inc(&slow_work_thread_count);
- p = kthread_run(slow_work_thread, NULL, "kslowd");
- if (IS_ERR(p)) {
- printk(KERN_DEBUG "Slow work thread pool: OOM\n");
- if (atomic_dec_and_test(&slow_work_thread_count))
- BUG(); /* we're running on a slow work thread... */
- mod_timer(&slow_work_oom_timer,
- round_jiffies(jiffies + SLOW_WORK_OOM_TIMEOUT));
- } else {
- /* ratelimit the starting of new threads */
- mod_timer(&slow_work_oom_timer, jiffies + 1);
- }
-
- mutex_unlock(&slow_work_user_lock);
-}
-
-static const struct slow_work_ops slow_work_new_thread_ops = {
- .owner = THIS_MODULE,
- .execute = slow_work_new_thread_execute,
-#ifdef CONFIG_SLOW_WORK_DEBUG
- .desc = slow_work_new_thread_desc,
-#endif
-};
-
-/*
- * post-OOM new thread start suppression expiration
- */
-static void slow_work_oom_timeout(unsigned long data)
-{
- slow_work_may_not_start_new_thread = false;
-}
-
-#ifdef CONFIG_SYSCTL
-/*
- * Handle adjustment of the minimum number of threads
- */
-static int slow_work_min_threads_sysctl(struct ctl_table *table, int write,
- void __user *buffer,
- size_t *lenp, loff_t *ppos)
-{
- int ret = proc_dointvec_minmax(table, write, 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)
- slow_work_schedule_cull();
- }
- 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,
- void __user *buffer,
- size_t *lenp, loff_t *ppos)
-{
- int ret = proc_dointvec_minmax(table, write, 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)
- slow_work_schedule_cull();
- }
- mutex_unlock(&slow_work_user_lock);
- }
-
- return ret;
-}
-#endif /* CONFIG_SYSCTL */
-
-/**
- * slow_work_register_user - Register a user of the facility
- * @module: The module about to make use 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(struct module *module)
-{
- 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);
-
-/*
- * wait for all outstanding items from the calling module to complete
- * - note that more items may be queued whilst we're waiting
- */
-static void slow_work_wait_for_items(struct module *module)
-{
-#ifdef CONFIG_MODULES
- DECLARE_WAITQUEUE(myself, current);
- struct slow_work *work;
- int loop;
-
- mutex_lock(&slow_work_unreg_sync_lock);
- add_wait_queue(&slow_work_unreg_wq, &myself);
-
- for (;;) {
- spin_lock_irq(&slow_work_queue_lock);
-
- /* first of all, we wait for the last queued item in each list
- * to be processed */
- list_for_each_entry_reverse(work, &vslow_work_queue, link) {
- if (work->owner == module) {
- set_current_state(TASK_UNINTERRUPTIBLE);
- slow_work_unreg_work_item = work;
- goto do_wait;
- }
- }
- list_for_each_entry_reverse(work, &slow_work_queue, link) {
- if (work->owner == module) {
- set_current_state(TASK_UNINTERRUPTIBLE);
- slow_work_unreg_work_item = work;
- goto do_wait;
- }
- }
-
- /* then we wait for the items being processed to finish */
- slow_work_unreg_module = module;
- smp_mb();
- for (loop = 0; loop < SLOW_WORK_THREAD_LIMIT; loop++) {
- if (slow_work_thread_processing[loop] == module)
- goto do_wait;
- }
- spin_unlock_irq(&slow_work_queue_lock);
- break; /* okay, we're done */
-
- do_wait:
- spin_unlock_irq(&slow_work_queue_lock);
- schedule();
- slow_work_unreg_work_item = NULL;
- slow_work_unreg_module = NULL;
- }
-
- remove_wait_queue(&slow_work_unreg_wq, &myself);
- mutex_unlock(&slow_work_unreg_sync_lock);
-#endif /* CONFIG_MODULES */
-}
-
-/**
- * slow_work_unregister_user - Unregister a user of the facility
- * @module: The module whose items should be cleared
- *
- * Unregister a user of the facility, killing all the threads if this was the
- * last one.
- *
- * This waits for all the work items belonging to the nominated module to go
- * away before proceeding.
- */
-void slow_work_unregister_user(struct module *module)
-{
- /* first of all, wait for all outstanding items from the calling module
- * to complete */
- if (module)
- slow_work_wait_for_items(module);
-
- /* then we can actually go about shutting down the facility if need
- * be */
- 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
-#ifdef CONFIG_SLOW_WORK_DEBUG
- {
- struct dentry *dbdir;
-
- dbdir = debugfs_create_dir("slow_work", NULL);
- if (dbdir && !IS_ERR(dbdir))
- debugfs_create_file("runqueue", S_IFREG | 0400, dbdir,
- NULL, &slow_work_runqueue_fops);
- }
-#endif
- return 0;
-}
-
-subsys_initcall(init_slow_work);
projects / cascardo / linux.git / commitdiff