Create a dynamically sized pool of threads for doing very slow work items
Create a dynamically sized pool of threads for doing very slow work items, such as invoking mkdir() or rmdir() - things that may take a long time and may sleep, holding mutexes/semaphores and hogging a thread, and are thus unsuitable for workqueues. The number of threads is always at least a settable minimum, but more are started when there's more work to do, up to a limit. Because of the nature of the load, it's not suitable for a 1-thread-per-CPU type pool. A system with one CPU may well want several threads. This is used by FS-Cache to do slow caching operations in the background, such as looking up, creating or deleting cache objects. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Serge Hallyn <serue@us.ibm.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com>
This commit is contained in:
David Howells
Родитель
8fe74cf053
Коммит
07fe7cb7c7
|
|
@ -0,0 +1,88 @@
|
|||
/* 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.
|
||||
*/
|
||||
|
||||
#ifndef _LINUX_SLOW_WORK_H
|
||||
#define _LINUX_SLOW_WORK_H
|
||||
|
||||
#ifdef CONFIG_SLOW_WORK
|
||||
|
||||
struct slow_work;
|
||||
|
||||
/*
|
||||
* The operations used to support slow work items
|
||||
*/
|
||||
struct slow_work_ops {
|
||||
/* get a ref on a work item
|
||||
* - return 0 if successful, -ve if not
|
||||
*/
|
||||
int (*get_ref)(struct slow_work *work);
|
||||
|
||||
/* discard a ref to a work item */
|
||||
void (*put_ref)(struct slow_work *work);
|
||||
|
||||
/* execute a work item */
|
||||
void (*execute)(struct slow_work *work);
|
||||
};
|
||||
|
||||
/*
|
||||
* A slow work item
|
||||
* - A reference is held on the parent object by the thread pool when it is
|
||||
* queued
|
||||
*/
|
||||
struct slow_work {
|
||||
unsigned long flags;
|
||||
#define SLOW_WORK_PENDING 0 /* item pending (further) execution */
|
||||
#define SLOW_WORK_EXECUTING 1 /* item currently executing */
|
||||
#define SLOW_WORK_ENQ_DEFERRED 2 /* item enqueue deferred */
|
||||
#define SLOW_WORK_VERY_SLOW 3 /* item is very slow */
|
||||
const struct slow_work_ops *ops; /* operations table for this item */
|
||||
struct list_head link; /* link in queue */
|
||||
};
|
||||
|
||||
/**
|
||||
* slow_work_init - Initialise a slow work item
|
||||
* @work: The work item to initialise
|
||||
* @ops: The operations to use to handle the slow work item
|
||||
*
|
||||
* Initialise a slow work item.
|
||||
*/
|
||||
static inline void slow_work_init(struct slow_work *work,
|
||||
const struct slow_work_ops *ops)
|
||||
{
|
||||
work->flags = 0;
|
||||
work->ops = ops;
|
||||
INIT_LIST_HEAD(&work->link);
|
||||
}
|
||||
|
||||
/**
|
||||
* slow_work_init - Initialise a very slow work item
|
||||
* @work: The work item to initialise
|
||||
* @ops: The operations to use to handle the slow work item
|
||||
*
|
||||
* Initialise a very slow work item. This item will be restricted such that
|
||||
* only a certain number of the pool threads will be able to execute items of
|
||||
* this type.
|
||||
*/
|
||||
static inline void vslow_work_init(struct slow_work *work,
|
||||
const struct slow_work_ops *ops)
|
||||
{
|
||||
work->flags = 1 << SLOW_WORK_VERY_SLOW;
|
||||
work->ops = ops;
|
||||
INIT_LIST_HEAD(&work->link);
|
||||
}
|
||||
|
||||
extern int slow_work_enqueue(struct slow_work *work);
|
||||
extern int slow_work_register_user(void);
|
||||
extern void slow_work_unregister_user(void);
|
||||
|
||||
|
||||
#endif /* CONFIG_SLOW_WORK */
|
||||
#endif /* _LINUX_SLOW_WORK_H */
|
||||
12
init/Kconfig
12
init/Kconfig
|
|
@ -1014,6 +1014,18 @@ config MARKERS
|
|||
|
||||
source "arch/Kconfig"
|
||||
|
||||
config SLOW_WORK
|
||||
default n
|
||||
bool "Enable slow work thread pool"
|
||||
help
|
||||
The slow work thread pool provides a number of dynamically allocated
|
||||
threads that can be used by the kernel to perform operations that
|
||||
take a relatively long time.
|
||||
|
||||
An example of this would be CacheFiles doing a path lookup followed
|
||||
by a series of mkdirs and a create call, all of which have to touch
|
||||
disk.
|
||||
|
||||
endmenu # General setup
|
||||
|
||||
config HAVE_GENERIC_DMA_COHERENT
|
||||
|
|
|
|||
|
|
@ -93,6 +93,7 @@ obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
|
|||
obj-$(CONFIG_FUNCTION_TRACER) += trace/
|
||||
obj-$(CONFIG_TRACING) += trace/
|
||||
obj-$(CONFIG_SMP) += sched_cpupri.o
|
||||
obj-$(CONFIG_SLOW_WORK) += slow-work.o
|
||||
|
||||
ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
|
||||
# According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
|
||||
|
|
|
|||
|
|
@ -0,0 +1,388 @@
|
|||
/* 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.
|
||||
*/
|
||||
|
||||
#include <linux/module.h>
|
||||
#include <linux/slow-work.h>
|
||||
#include <linux/kthread.h>
|
||||
#include <linux/freezer.h>
|
||||
#include <linux/wait.h>
|
||||
#include <asm/system.h>
|
||||
|
||||
/*
|
||||
* 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 */
|
||||
static atomic_t slow_work_thread_count;
|
||||
static atomic_t vslow_work_executing_count;
|
||||
|
||||
/*
|
||||
* 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.
|
||||
*/
|
||||
static LIST_HEAD(slow_work_queue);
|
||||
static LIST_HEAD(vslow_work_queue);
|
||||
static DEFINE_SPINLOCK(slow_work_queue_lock);
|
||||
|
||||
/*
|
||||
* 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);
|
||||
|
||||
/*
|
||||
* 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 bool slow_work_execute(void)
|
||||
{
|
||||
struct slow_work *work = NULL;
|
||||
unsigned vsmax;
|
||||
bool very_slow;
|
||||
|
||||
vsmax = slow_work_calc_vsmax();
|
||||
|
||||
/* 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 */
|
||||
}
|
||||
spin_unlock_irq(&slow_work_queue_lock);
|
||||
|
||||
if (!work)
|
||||
return false;
|
||||
|
||||
if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
|
||||
BUG();
|
||||
|
||||
work->ops->execute(work);
|
||||
|
||||
if (very_slow)
|
||||
atomic_dec(&vslow_work_executing_count);
|
||||
clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
|
||||
|
||||
/* 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);
|
||||
}
|
||||
|
||||
work->ops->put_ref(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
|
||||
*/
|
||||
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);
|
||||
return true;
|
||||
}
|
||||
|
||||
/**
|
||||
* 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.
|
||||
*/
|
||||
int slow_work_enqueue(struct slow_work *work)
|
||||
{
|
||||
unsigned long flags;
|
||||
|
||||
BUG_ON(slow_work_user_count <= 0);
|
||||
BUG_ON(!work);
|
||||
BUG_ON(!work->ops);
|
||||
BUG_ON(!work->ops->get_ref);
|
||||
|
||||
/* 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)) {
|
||||
spin_lock_irqsave(&slow_work_queue_lock, flags);
|
||||
|
||||
/* 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 {
|
||||
if (work->ops->get_ref(work) < 0)
|
||||
goto cant_get_ref;
|
||||
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);
|
||||
wake_up(&slow_work_thread_wq);
|
||||
}
|
||||
|
||||
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
|
||||
}
|
||||
return 0;
|
||||
|
||||
cant_get_ref:
|
||||
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
|
||||
return -EAGAIN;
|
||||
}
|
||||
EXPORT_SYMBOL(slow_work_enqueue);
|
||||
|
||||
/*
|
||||
* 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;
|
||||
|
||||
DEFINE_WAIT(wait);
|
||||
|
||||
set_freezable();
|
||||
set_user_nice(current, -5);
|
||||
|
||||
for (;;) {
|
||||
vsmax = vslow_work_proportion;
|
||||
vsmax *= atomic_read(&slow_work_thread_count);
|
||||
vsmax /= 100;
|
||||
|
||||
prepare_to_wait(&slow_work_thread_wq, &wait,
|
||||
TASK_INTERRUPTIBLE);
|
||||
if (!freezing(current) &&
|
||||
!slow_work_threads_should_exit &&
|
||||
!slow_work_available(vsmax))
|
||||
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()) {
|
||||
cond_resched();
|
||||
continue;
|
||||
}
|
||||
|
||||
if (slow_work_threads_should_exit)
|
||||
break;
|
||||
}
|
||||
|
||||
if (atomic_dec_and_test(&slow_work_thread_count))
|
||||
complete_and_exit(&slow_work_last_thread_exited, 0);
|
||||
return 0;
|
||||
}
|
||||
|
||||
/**
|
||||
* 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;
|
||||
|
||||
/* 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;
|
||||
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 (nr_cpus > slow_work_max_threads)
|
||||
slow_work_max_threads = nr_cpus;
|
||||
return 0;
|
||||
}
|
||||
|
||||
subsys_initcall(init_slow_work);
|
||||
Загрузка…
Ссылка в новой задаче