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authorIngo Molnar <mingo@elte.hu>2009-04-08 11:02:50 -0400
committerIngo Molnar <mingo@elte.hu>2009-04-08 11:02:57 -0400
commitff96e612cba32510e263e17b213235fe5746397e (patch)
treea8df57d76b10e0901a4fb76cd2987eb9826a560a /kernel/slow-work.c
parentcd84a42f315e50edd454c27a3da3951ccd3d735a (diff)
parent577c9c456f0e1371cbade38eaf91ae8e8a308555 (diff)
Merge commit 'v2.6.30-rc1' into core/urgent
Merge reason: need latest upstream to queue up dependent fix Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/slow-work.c')
-rw-r--r--kernel/slow-work.c640
1 files changed, 640 insertions, 0 deletions
diff --git a/kernel/slow-work.c b/kernel/slow-work.c
new file mode 100644
index 000000000000..cf2bc01186ef
--- /dev/null
+++ b/kernel/slow-work.c
@@ -0,0 +1,640 @@
1/* Worker thread pool for slow items, such as filesystem lookups or mkdirs
2 *
3 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
10 *
11 * See Documentation/slow-work.txt
12 */
13
14#include <linux/module.h>
15#include <linux/slow-work.h>
16#include <linux/kthread.h>
17#include <linux/freezer.h>
18#include <linux/wait.h>
19
20#define SLOW_WORK_CULL_TIMEOUT (5 * HZ) /* cull threads 5s after running out of
21 * things to do */
22#define SLOW_WORK_OOM_TIMEOUT (5 * HZ) /* can't start new threads for 5s after
23 * OOM */
24
25static void slow_work_cull_timeout(unsigned long);
26static void slow_work_oom_timeout(unsigned long);
27
28#ifdef CONFIG_SYSCTL
29static int slow_work_min_threads_sysctl(struct ctl_table *, int, struct file *,
30 void __user *, size_t *, loff_t *);
31
32static int slow_work_max_threads_sysctl(struct ctl_table *, int , struct file *,
33 void __user *, size_t *, loff_t *);
34#endif
35
36/*
37 * The pool of threads has at least min threads in it as long as someone is
38 * using the facility, and may have as many as max.
39 *
40 * A portion of the pool may be processing very slow operations.
41 */
42static unsigned slow_work_min_threads = 2;
43static unsigned slow_work_max_threads = 4;
44static unsigned vslow_work_proportion = 50; /* % of threads that may process
45 * very slow work */
46
47#ifdef CONFIG_SYSCTL
48static const int slow_work_min_min_threads = 2;
49static int slow_work_max_max_threads = 255;
50static const int slow_work_min_vslow = 1;
51static const int slow_work_max_vslow = 99;
52
53ctl_table slow_work_sysctls[] = {
54 {
55 .ctl_name = CTL_UNNUMBERED,
56 .procname = "min-threads",
57 .data = &slow_work_min_threads,
58 .maxlen = sizeof(unsigned),
59 .mode = 0644,
60 .proc_handler = slow_work_min_threads_sysctl,
61 .extra1 = (void *) &slow_work_min_min_threads,
62 .extra2 = &slow_work_max_threads,
63 },
64 {
65 .ctl_name = CTL_UNNUMBERED,
66 .procname = "max-threads",
67 .data = &slow_work_max_threads,
68 .maxlen = sizeof(unsigned),
69 .mode = 0644,
70 .proc_handler = slow_work_max_threads_sysctl,
71 .extra1 = &slow_work_min_threads,
72 .extra2 = (void *) &slow_work_max_max_threads,
73 },
74 {
75 .ctl_name = CTL_UNNUMBERED,
76 .procname = "vslow-percentage",
77 .data = &vslow_work_proportion,
78 .maxlen = sizeof(unsigned),
79 .mode = 0644,
80 .proc_handler = &proc_dointvec_minmax,
81 .extra1 = (void *) &slow_work_min_vslow,
82 .extra2 = (void *) &slow_work_max_vslow,
83 },
84 { .ctl_name = 0 }
85};
86#endif
87
88/*
89 * The active state of the thread pool
90 */
91static atomic_t slow_work_thread_count;
92static atomic_t vslow_work_executing_count;
93
94static bool slow_work_may_not_start_new_thread;
95static bool slow_work_cull; /* cull a thread due to lack of activity */
96static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
97static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
98static struct slow_work slow_work_new_thread; /* new thread starter */
99
100/*
101 * The queues of work items and the lock governing access to them. These are
102 * shared between all the CPUs. It doesn't make sense to have per-CPU queues
103 * as the number of threads bears no relation to the number of CPUs.
104 *
105 * There are two queues of work items: one for slow work items, and one for
106 * very slow work items.
107 */
108static LIST_HEAD(slow_work_queue);
109static LIST_HEAD(vslow_work_queue);
110static DEFINE_SPINLOCK(slow_work_queue_lock);
111
112/*
113 * The thread controls. A variable used to signal to the threads that they
114 * should exit when the queue is empty, a waitqueue used by the threads to wait
115 * for signals, and a completion set by the last thread to exit.
116 */
117static bool slow_work_threads_should_exit;
118static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);
119static DECLARE_COMPLETION(slow_work_last_thread_exited);
120
121/*
122 * The number of users of the thread pool and its lock. Whilst this is zero we
123 * have no threads hanging around, and when this reaches zero, we wait for all
124 * active or queued work items to complete and kill all the threads we do have.
125 */
126static int slow_work_user_count;
127static DEFINE_MUTEX(slow_work_user_lock);
128
129/*
130 * Calculate the maximum number of active threads in the pool that are
131 * permitted to process very slow work items.
132 *
133 * The answer is rounded up to at least 1, but may not equal or exceed the
134 * maximum number of the threads in the pool. This means we always have at
135 * least one thread that can process slow work items, and we always have at
136 * least one thread that won't get tied up doing so.
137 */
138static unsigned slow_work_calc_vsmax(void)
139{
140 unsigned vsmax;
141
142 vsmax = atomic_read(&slow_work_thread_count) * vslow_work_proportion;
143 vsmax /= 100;
144 vsmax = max(vsmax, 1U);
145 return min(vsmax, slow_work_max_threads - 1);
146}
147
148/*
149 * Attempt to execute stuff queued on a slow thread. Return true if we managed
150 * it, false if there was nothing to do.
151 */
152static bool slow_work_execute(void)
153{
154 struct slow_work *work = NULL;
155 unsigned vsmax;
156 bool very_slow;
157
158 vsmax = slow_work_calc_vsmax();
159
160 /* see if we can schedule a new thread to be started if we're not
161 * keeping up with the work */
162 if (!waitqueue_active(&slow_work_thread_wq) &&
163 (!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&
164 atomic_read(&slow_work_thread_count) < slow_work_max_threads &&
165 !slow_work_may_not_start_new_thread)
166 slow_work_enqueue(&slow_work_new_thread);
167
168 /* find something to execute */
169 spin_lock_irq(&slow_work_queue_lock);
170 if (!list_empty(&vslow_work_queue) &&
171 atomic_read(&vslow_work_executing_count) < vsmax) {
172 work = list_entry(vslow_work_queue.next,
173 struct slow_work, link);
174 if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
175 BUG();
176 list_del_init(&work->link);
177 atomic_inc(&vslow_work_executing_count);
178 very_slow = true;
179 } else if (!list_empty(&slow_work_queue)) {
180 work = list_entry(slow_work_queue.next,
181 struct slow_work, link);
182 if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
183 BUG();
184 list_del_init(&work->link);
185 very_slow = false;
186 } else {
187 very_slow = false; /* avoid the compiler warning */
188 }
189 spin_unlock_irq(&slow_work_queue_lock);
190
191 if (!work)
192 return false;
193
194 if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
195 BUG();
196
197 work->ops->execute(work);
198
199 if (very_slow)
200 atomic_dec(&vslow_work_executing_count);
201 clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
202
203 /* if someone tried to enqueue the item whilst we were executing it,
204 * then it'll be left unenqueued to avoid multiple threads trying to
205 * execute it simultaneously
206 *
207 * there is, however, a race between us testing the pending flag and
208 * getting the spinlock, and between the enqueuer setting the pending
209 * flag and getting the spinlock, so we use a deferral bit to tell us
210 * if the enqueuer got there first
211 */
212 if (test_bit(SLOW_WORK_PENDING, &work->flags)) {
213 spin_lock_irq(&slow_work_queue_lock);
214
215 if (!test_bit(SLOW_WORK_EXECUTING, &work->flags) &&
216 test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags))
217 goto auto_requeue;
218
219 spin_unlock_irq(&slow_work_queue_lock);
220 }
221
222 work->ops->put_ref(work);
223 return true;
224
225auto_requeue:
226 /* we must complete the enqueue operation
227 * - we transfer our ref on the item back to the appropriate queue
228 * - don't wake another thread up as we're awake already
229 */
230 if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
231 list_add_tail(&work->link, &vslow_work_queue);
232 else
233 list_add_tail(&work->link, &slow_work_queue);
234 spin_unlock_irq(&slow_work_queue_lock);
235 return true;
236}
237
238/**
239 * slow_work_enqueue - Schedule a slow work item for processing
240 * @work: The work item to queue
241 *
242 * Schedule a slow work item for processing. If the item is already undergoing
243 * execution, this guarantees not to re-enter the execution routine until the
244 * first execution finishes.
245 *
246 * The item is pinned by this function as it retains a reference to it, managed
247 * through the item operations. The item is unpinned once it has been
248 * executed.
249 *
250 * An item may hog the thread that is running it for a relatively large amount
251 * of time, sufficient, for example, to perform several lookup, mkdir, create
252 * and setxattr operations. It may sleep on I/O and may sleep to obtain locks.
253 *
254 * Conversely, if a number of items are awaiting processing, it may take some
255 * time before any given item is given attention. The number of threads in the
256 * pool may be increased to deal with demand, but only up to a limit.
257 *
258 * If SLOW_WORK_VERY_SLOW is set on the work item, then it will be placed in
259 * the very slow queue, from which only a portion of the threads will be
260 * allowed to pick items to execute. This ensures that very slow items won't
261 * overly block ones that are just ordinarily slow.
262 *
263 * Returns 0 if successful, -EAGAIN if not.
264 */
265int slow_work_enqueue(struct slow_work *work)
266{
267 unsigned long flags;
268
269 BUG_ON(slow_work_user_count <= 0);
270 BUG_ON(!work);
271 BUG_ON(!work->ops);
272 BUG_ON(!work->ops->get_ref);
273
274 /* when honouring an enqueue request, we only promise that we will run
275 * the work function in the future; we do not promise to run it once
276 * per enqueue request
277 *
278 * we use the PENDING bit to merge together repeat requests without
279 * having to disable IRQs and take the spinlock, whilst still
280 * maintaining our promise
281 */
282 if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
283 spin_lock_irqsave(&slow_work_queue_lock, flags);
284
285 /* we promise that we will not attempt to execute the work
286 * function in more than one thread simultaneously
287 *
288 * this, however, leaves us with a problem if we're asked to
289 * enqueue the work whilst someone is executing the work
290 * function as simply queueing the work immediately means that
291 * another thread may try executing it whilst it is already
292 * under execution
293 *
294 * to deal with this, we set the ENQ_DEFERRED bit instead of
295 * enqueueing, and the thread currently executing the work
296 * function will enqueue the work item when the work function
297 * returns and it has cleared the EXECUTING bit
298 */
299 if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
300 set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
301 } else {
302 if (work->ops->get_ref(work) < 0)
303 goto cant_get_ref;
304 if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
305 list_add_tail(&work->link, &vslow_work_queue);
306 else
307 list_add_tail(&work->link, &slow_work_queue);
308 wake_up(&slow_work_thread_wq);
309 }
310
311 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
312 }
313 return 0;
314
315cant_get_ref:
316 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
317 return -EAGAIN;
318}
319EXPORT_SYMBOL(slow_work_enqueue);
320
321/*
322 * Worker thread culling algorithm
323 */
324static bool slow_work_cull_thread(void)
325{
326 unsigned long flags;
327 bool do_cull = false;
328
329 spin_lock_irqsave(&slow_work_queue_lock, flags);
330
331 if (slow_work_cull) {
332 slow_work_cull = false;
333
334 if (list_empty(&slow_work_queue) &&
335 list_empty(&vslow_work_queue) &&
336 atomic_read(&slow_work_thread_count) >
337 slow_work_min_threads) {
338 mod_timer(&slow_work_cull_timer,
339 jiffies + SLOW_WORK_CULL_TIMEOUT);
340 do_cull = true;
341 }
342 }
343
344 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
345 return do_cull;
346}
347
348/*
349 * Determine if there is slow work available for dispatch
350 */
351static inline bool slow_work_available(int vsmax)
352{
353 return !list_empty(&slow_work_queue) ||
354 (!list_empty(&vslow_work_queue) &&
355 atomic_read(&vslow_work_executing_count) < vsmax);
356}
357
358/*
359 * Worker thread dispatcher
360 */
361static int slow_work_thread(void *_data)
362{
363 int vsmax;
364
365 DEFINE_WAIT(wait);
366
367 set_freezable();
368 set_user_nice(current, -5);
369
370 for (;;) {
371 vsmax = vslow_work_proportion;
372 vsmax *= atomic_read(&slow_work_thread_count);
373 vsmax /= 100;
374
375 prepare_to_wait(&slow_work_thread_wq, &wait,
376 TASK_INTERRUPTIBLE);
377 if (!freezing(current) &&
378 !slow_work_threads_should_exit &&
379 !slow_work_available(vsmax) &&
380 !slow_work_cull)
381 schedule();
382 finish_wait(&slow_work_thread_wq, &wait);
383
384 try_to_freeze();
385
386 vsmax = vslow_work_proportion;
387 vsmax *= atomic_read(&slow_work_thread_count);
388 vsmax /= 100;
389
390 if (slow_work_available(vsmax) && slow_work_execute()) {
391 cond_resched();
392 if (list_empty(&slow_work_queue) &&
393 list_empty(&vslow_work_queue) &&
394 atomic_read(&slow_work_thread_count) >
395 slow_work_min_threads)
396 mod_timer(&slow_work_cull_timer,
397 jiffies + SLOW_WORK_CULL_TIMEOUT);
398 continue;
399 }
400
401 if (slow_work_threads_should_exit)
402 break;
403
404 if (slow_work_cull && slow_work_cull_thread())
405 break;
406 }
407
408 if (atomic_dec_and_test(&slow_work_thread_count))
409 complete_and_exit(&slow_work_last_thread_exited, 0);
410 return 0;
411}
412
413/*
414 * Handle thread cull timer expiration
415 */
416static void slow_work_cull_timeout(unsigned long data)
417{
418 slow_work_cull = true;
419 wake_up(&slow_work_thread_wq);
420}
421
422/*
423 * Get a reference on slow work thread starter
424 */
425static int slow_work_new_thread_get_ref(struct slow_work *work)
426{
427 return 0;
428}
429
430/*
431 * Drop a reference on slow work thread starter
432 */
433static void slow_work_new_thread_put_ref(struct slow_work *work)
434{
435}
436
437/*
438 * Start a new slow work thread
439 */
440static void slow_work_new_thread_execute(struct slow_work *work)
441{
442 struct task_struct *p;
443
444 if (slow_work_threads_should_exit)
445 return;
446
447 if (atomic_read(&slow_work_thread_count) >= slow_work_max_threads)
448 return;
449
450 if (!mutex_trylock(&slow_work_user_lock))
451 return;
452
453 slow_work_may_not_start_new_thread = true;
454 atomic_inc(&slow_work_thread_count);
455 p = kthread_run(slow_work_thread, NULL, "kslowd");
456 if (IS_ERR(p)) {
457 printk(KERN_DEBUG "Slow work thread pool: OOM\n");
458 if (atomic_dec_and_test(&slow_work_thread_count))
459 BUG(); /* we're running on a slow work thread... */
460 mod_timer(&slow_work_oom_timer,
461 jiffies + SLOW_WORK_OOM_TIMEOUT);
462 } else {
463 /* ratelimit the starting of new threads */
464 mod_timer(&slow_work_oom_timer, jiffies + 1);
465 }
466
467 mutex_unlock(&slow_work_user_lock);
468}
469
470static const struct slow_work_ops slow_work_new_thread_ops = {
471 .get_ref = slow_work_new_thread_get_ref,
472 .put_ref = slow_work_new_thread_put_ref,
473 .execute = slow_work_new_thread_execute,
474};
475
476/*
477 * post-OOM new thread start suppression expiration
478 */
479static void slow_work_oom_timeout(unsigned long data)
480{
481 slow_work_may_not_start_new_thread = false;
482}
483
484#ifdef CONFIG_SYSCTL
485/*
486 * Handle adjustment of the minimum number of threads
487 */
488static int slow_work_min_threads_sysctl(struct ctl_table *table, int write,
489 struct file *filp, void __user *buffer,
490 size_t *lenp, loff_t *ppos)
491{
492 int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
493 int n;
494
495 if (ret == 0) {
496 mutex_lock(&slow_work_user_lock);
497 if (slow_work_user_count > 0) {
498 /* see if we need to start or stop threads */
499 n = atomic_read(&slow_work_thread_count) -
500 slow_work_min_threads;
501
502 if (n < 0 && !slow_work_may_not_start_new_thread)
503 slow_work_enqueue(&slow_work_new_thread);
504 else if (n > 0)
505 mod_timer(&slow_work_cull_timer,
506 jiffies + SLOW_WORK_CULL_TIMEOUT);
507 }
508 mutex_unlock(&slow_work_user_lock);
509 }
510
511 return ret;
512}
513
514/*
515 * Handle adjustment of the maximum number of threads
516 */
517static int slow_work_max_threads_sysctl(struct ctl_table *table, int write,
518 struct file *filp, void __user *buffer,
519 size_t *lenp, loff_t *ppos)
520{
521 int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
522 int n;
523
524 if (ret == 0) {
525 mutex_lock(&slow_work_user_lock);
526 if (slow_work_user_count > 0) {
527 /* see if we need to stop threads */
528 n = slow_work_max_threads -
529 atomic_read(&slow_work_thread_count);
530
531 if (n < 0)
532 mod_timer(&slow_work_cull_timer,
533 jiffies + SLOW_WORK_CULL_TIMEOUT);
534 }
535 mutex_unlock(&slow_work_user_lock);
536 }
537
538 return ret;
539}
540#endif /* CONFIG_SYSCTL */
541
542/**
543 * slow_work_register_user - Register a user of the facility
544 *
545 * Register a user of the facility, starting up the initial threads if there
546 * aren't any other users at this point. This will return 0 if successful, or
547 * an error if not.
548 */
549int slow_work_register_user(void)
550{
551 struct task_struct *p;
552 int loop;
553
554 mutex_lock(&slow_work_user_lock);
555
556 if (slow_work_user_count == 0) {
557 printk(KERN_NOTICE "Slow work thread pool: Starting up\n");
558 init_completion(&slow_work_last_thread_exited);
559
560 slow_work_threads_should_exit = false;
561 slow_work_init(&slow_work_new_thread,
562 &slow_work_new_thread_ops);
563 slow_work_may_not_start_new_thread = false;
564 slow_work_cull = false;
565
566 /* start the minimum number of threads */
567 for (loop = 0; loop < slow_work_min_threads; loop++) {
568 atomic_inc(&slow_work_thread_count);
569 p = kthread_run(slow_work_thread, NULL, "kslowd");
570 if (IS_ERR(p))
571 goto error;
572 }
573 printk(KERN_NOTICE "Slow work thread pool: Ready\n");
574 }
575
576 slow_work_user_count++;
577 mutex_unlock(&slow_work_user_lock);
578 return 0;
579
580error:
581 if (atomic_dec_and_test(&slow_work_thread_count))
582 complete(&slow_work_last_thread_exited);
583 if (loop > 0) {
584 printk(KERN_ERR "Slow work thread pool:"
585 " Aborting startup on ENOMEM\n");
586 slow_work_threads_should_exit = true;
587 wake_up_all(&slow_work_thread_wq);
588 wait_for_completion(&slow_work_last_thread_exited);
589 printk(KERN_ERR "Slow work thread pool: Aborted\n");
590 }
591 mutex_unlock(&slow_work_user_lock);
592 return PTR_ERR(p);
593}
594EXPORT_SYMBOL(slow_work_register_user);
595
596/**
597 * slow_work_unregister_user - Unregister a user of the facility
598 *
599 * Unregister a user of the facility, killing all the threads if this was the
600 * last one.
601 */
602void slow_work_unregister_user(void)
603{
604 mutex_lock(&slow_work_user_lock);
605
606 BUG_ON(slow_work_user_count <= 0);
607
608 slow_work_user_count--;
609 if (slow_work_user_count == 0) {
610 printk(KERN_NOTICE "Slow work thread pool: Shutting down\n");
611 slow_work_threads_should_exit = true;
612 wake_up_all(&slow_work_thread_wq);
613 wait_for_completion(&slow_work_last_thread_exited);
614 printk(KERN_NOTICE "Slow work thread pool:"
615 " Shut down complete\n");
616 }
617
618 del_timer_sync(&slow_work_cull_timer);
619
620 mutex_unlock(&slow_work_user_lock);
621}
622EXPORT_SYMBOL(slow_work_unregister_user);
623
624/*
625 * Initialise the slow work facility
626 */
627static int __init init_slow_work(void)
628{
629 unsigned nr_cpus = num_possible_cpus();
630
631 if (slow_work_max_threads < nr_cpus)
632 slow_work_max_threads = nr_cpus;
633#ifdef CONFIG_SYSCTL
634 if (slow_work_max_max_threads < nr_cpus * 2)
635 slow_work_max_max_threads = nr_cpus * 2;
636#endif
637 return 0;
638}
639
640subsys_initcall(init_slow_work);