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Make taskq_member() use ->journal_info

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The ->journal_info pointer in the task_struct is reserved for use by
filesystems and because the kernel can have multiple file systems on the
same stack due to direct reclaim, each filesystem that touches
->journal_info in a callback function will save the value at the start
of its frame and restore it at the end of its frame.  This allows us to
safely use ->journal_info to store a pointer to the taskq's struct in
taskq threads so that ZFS code paths can detect the presence of a taskq.
This could break if the ZFS code were to use taskq_member from the
context of direct reclaim. However, there are no such uses of it in that
manner, so this is safe.

This eliminates an O(N) list traversal under a spinlock with an O(1)
unlocked pointer comparison.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: tuxoko <tuxoko@gmail.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes #500
This commit is contained in:
Richard Yao 2015-12-03 14:15:16 -05:00 committed by Brian Behlendorf
parent 1683e75edc
commit a430c11f0b
2 changed files with 4 additions and 35 deletions
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2
include/sys/taskq.h
View File

@ -124,7 +124,7 @@ extern void taskq_wait_id(taskq_t *, taskqid_t);
extern void taskq_wait_outstanding(taskq_t *, taskqid_t);
extern void taskq_wait(taskq_t *);
extern int taskq_cancel_id(taskq_t *, taskqid_t);
extern int taskq_member(taskq_t *, void *);
#define taskq_member(taskq, thread) ((taskq) == ((thread)->journal_info))
#define taskq_create_proc(name, nthreads, pri, min, max, proc, flags) \
taskq_create(name, nthreads, pri, min, max, flags)

37
module/spl/spl-taskq.c
View File

@ -448,40 +448,6 @@ taskq_wait(taskq_t *tq)
}
EXPORT_SYMBOL(taskq_wait);
static int
taskq_member_impl(taskq_t *tq, void *t)
{
struct list_head *l;
taskq_thread_t *tqt;
int found = 0;
ASSERT(tq);
ASSERT(t);
ASSERT(spin_is_locked(&tq->tq_lock));
list_for_each(l, &tq->tq_thread_list) {
tqt = list_entry(l, taskq_thread_t, tqt_thread_list);
if (tqt->tqt_thread == (struct task_struct *)t) {
found = 1;
break;
}
}
return (found);
}
int
taskq_member(taskq_t *tq, void *t)
{
int found;
spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
found = taskq_member_impl(tq, t);
spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
return (found);
}
EXPORT_SYMBOL(taskq_member);
/*
* Cancel an already dispatched task given the task id. Still pending tasks
* will be immediately canceled, and if the task is active the function will
@ -812,6 +778,7 @@ taskq_thread(void *args)
ASSERT(tqt);
tq = tqt->tqt_tq;
current->flags |= PF_NOFREEZE;
current->journal_info = tq;
#if defined(PF_MEMALLOC_NOIO)
(void) memalloc_noio_save();
@ -877,6 +844,8 @@ taskq_thread(void *args)
/* Perform the requested task */
t->tqent_func(t->tqent_arg);
ASSERT3P(tq, ==, current->journal_info);
spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
tq->tq_nactive--;
list_del_init(&tqt->tqt_active_list);