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writeback: optimize periodic bdi thread wakeups 

Whe the first inode for a bdi is marked dirty, we wake up the bdi thread which
should take care of the periodic background write-out. However, the write-out
will actually start only 'dirty_writeback_interval' centisecs later, so we can
delay the wake-up.

This change was requested by Nick Piggin who pointed out that if we delay the
wake-up, we weed out 2 unnecessary contex switches, which matters because
'__mark_inode_dirty()' is a hot-path function.

This patch introduces a new function - 'bdi_wakeup_thread_delayed()', which
sets up a timer to wake-up the bdi thread and returns. So the wake-up is
delayed.

We also delete the timer in bdi threads just before writing-back. And
synchronously delete it when unregistering bdi. At the unregister point the bdi
does not have any users, so no one can arm it again.

Since now we take 'bdi->wb_lock' in the timer, which can execute in softirq
context, we have to use 'spin_lock_bh()' for 'bdi->wb_lock'. This patch makes
this change as well.

This patch also moves the 'bdi_wb_init()' function down in the file to avoid
forward-declaration of 'bdi_wakeup_thread_delayed()'.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Artem Bityutskiy 2010-07-25 14:29:22 +03:00 committed by Jens Axboe
parent 253c34e9b1
commit 6467716a37
3 changed files with 70 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
fs/fs-writeback.c
View File

@ -76,7 +76,7 @@ static void bdi_queue_work(struct backing_dev_info *bdi,
{
trace_writeback_queue(bdi, work);
spin_lock(&bdi->wb_lock);
spin_lock_bh(&bdi->wb_lock);
list_add_tail(&work->list, &bdi->work_list);
if (bdi->wb.task) {
wake_up_process(bdi->wb.task);
@ -88,7 +88,7 @@ static void bdi_queue_work(struct backing_dev_info *bdi,
trace_writeback_nothread(bdi, work);
wake_up_process(default_backing_dev_info.wb.task);
}
spin_unlock(&bdi->wb_lock);
spin_unlock_bh(&bdi->wb_lock);
}
static void
@ -704,13 +704,13 @@ get_next_work_item(struct backing_dev_info *bdi)
{
struct wb_writeback_work *work = NULL;
spin_lock(&bdi->wb_lock);
spin_lock_bh(&bdi->wb_lock);
if (!list_empty(&bdi->work_list)) {
work = list_entry(bdi->work_list.next,
struct wb_writeback_work, list);
list_del_init(&work->list);
}
spin_unlock(&bdi->wb_lock);
spin_unlock_bh(&bdi->wb_lock);
return work;
}
@ -810,6 +810,12 @@ int bdi_writeback_thread(void *data)
trace_writeback_thread_start(bdi);
while (!kthread_should_stop()) {
/*
* Remove own delayed wake-up timer, since we are already awake
* and we'll take care of the preriodic write-back.
*/
del_timer(&wb->wakeup_timer);
pages_written = wb_do_writeback(wb, 0);
trace_writeback_pages_written(pages_written);
@ -868,26 +874,6 @@ void wakeup_flusher_threads(long nr_pages)
rcu_read_unlock();
}
/*
* This function is used when the first inode for this bdi is marked dirty. It
* wakes-up the corresponding bdi thread which should then take care of the
* periodic background write-out of dirty inodes.
*/
static void wakeup_bdi_thread(struct backing_dev_info *bdi)
{
spin_lock(&bdi->wb_lock);
if (bdi->wb.task)
wake_up_process(bdi->wb.task);
else
/*
* When bdi tasks are inactive for long time, they are killed.
* In this case we have to wake-up the forker thread which
* should create and run the bdi thread.
*/
wake_up_process(default_backing_dev_info.wb.task);
spin_unlock(&bdi->wb_lock);
}
static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
@ -1019,7 +1005,7 @@ out:
spin_unlock(&inode_lock);
if (wakeup_bdi)
wakeup_bdi_thread(bdi);
bdi_wakeup_thread_delayed(bdi);
}
EXPORT_SYMBOL(__mark_inode_dirty);

2
include/linux/backing-dev.h
View File

@ -52,6 +52,7 @@ struct bdi_writeback {
unsigned long last_active; /* last time bdi thread was active */
struct task_struct *task; /* writeback thread */
struct timer_list wakeup_timer; /* used for delayed bdi thread wakeup */
struct list_head b_dirty; /* dirty inodes */
struct list_head b_io; /* parked for writeback */
struct list_head b_more_io; /* parked for more writeback */
@ -105,6 +106,7 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi);
int bdi_writeback_thread(void *data);
int bdi_has_dirty_io(struct backing_dev_info *bdi);
void bdi_arm_supers_timer(void);
void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi);
extern spinlock_t bdi_lock;
extern struct list_head bdi_list;

73
mm/backing-dev.c
View File

@ -248,17 +248,6 @@ static int __init default_bdi_init(void)
}
subsys_initcall(default_bdi_init);
static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
{
memset(wb, 0, sizeof(*wb));
wb->bdi = bdi;
wb->last_old_flush = jiffies;
INIT_LIST_HEAD(&wb->b_dirty);
INIT_LIST_HEAD(&wb->b_io);
INIT_LIST_HEAD(&wb->b_more_io);
}
int bdi_has_dirty_io(struct backing_dev_info *bdi)
{
return wb_has_dirty_io(&bdi->wb);
@ -316,6 +305,43 @@ static void sync_supers_timer_fn(unsigned long unused)
bdi_arm_supers_timer();
}
static void wakeup_timer_fn(unsigned long data)
{
struct backing_dev_info *bdi = (struct backing_dev_info *)data;
spin_lock_bh(&bdi->wb_lock);
if (bdi->wb.task) {
wake_up_process(bdi->wb.task);
} else {
/*
* When bdi tasks are inactive for long time, they are killed.
* In this case we have to wake-up the forker thread which
* should create and run the bdi thread.
*/
wake_up_process(default_backing_dev_info.wb.task);
}
spin_unlock_bh(&bdi->wb_lock);
}
/*
* This function is used when the first inode for this bdi is marked dirty. It
* wakes-up the corresponding bdi thread which should then take care of the
* periodic background write-out of dirty inodes. Since the write-out would
* starts only 'dirty_writeback_interval' centisecs from now anyway, we just
* set up a timer which wakes the bdi thread up later.
*
* Note, we wouldn't bother setting up the timer, but this function is on the
* fast-path (used by '__mark_inode_dirty()'), so we save few context switches
* by delaying the wake-up.
*/
void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
{
unsigned long timeout;
timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
}
/*
* Calculate the longest interval (jiffies) bdi threads are allowed to be
* inactive.
@ -353,8 +379,10 @@ static int bdi_forker_thread(void *ptr)
* Temporary measure, we want to make sure we don't see
* dirty data on the default backing_dev_info
*/
if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
del_timer(&me->wakeup_timer);
wb_do_writeback(me, 0);
}
spin_lock_bh(&bdi_lock);
set_current_state(TASK_INTERRUPTIBLE);
@ -386,7 +414,7 @@ static int bdi_forker_thread(void *ptr)
break;
}
spin_lock(&bdi->wb_lock);
spin_lock_bh(&bdi->wb_lock);
/*
* If there is no work to do and the bdi thread was
* inactive long enough - kill it. The wb_lock is taken
@ -403,7 +431,7 @@ static int bdi_forker_thread(void *ptr)
action = KILL_THREAD;
break;
}
spin_unlock(&bdi->wb_lock);
spin_unlock_bh(&bdi->wb_lock);
}
spin_unlock_bh(&bdi_lock);
@ -427,9 +455,9 @@ static int bdi_forker_thread(void *ptr)
* The spinlock makes sure we do not lose
* wake-ups when racing with 'bdi_queue_work()'.
*/
spin_lock(&bdi->wb_lock);
spin_lock_bh(&bdi->wb_lock);
bdi->wb.task = task;
spin_unlock(&bdi->wb_lock);
spin_unlock_bh(&bdi->wb_lock);
}
break;
@ -586,6 +614,7 @@ void bdi_unregister(struct backing_dev_info *bdi)
if (bdi->dev) {
trace_writeback_bdi_unregister(bdi);
bdi_prune_sb(bdi);
del_timer_sync(&bdi->wb.wakeup_timer);
if (!bdi_cap_flush_forker(bdi))
bdi_wb_shutdown(bdi);
@ -596,6 +625,18 @@ void bdi_unregister(struct backing_dev_info *bdi)
}
EXPORT_SYMBOL(bdi_unregister);
static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
{
memset(wb, 0, sizeof(*wb));
wb->bdi = bdi;
wb->last_old_flush = jiffies;
INIT_LIST_HEAD(&wb->b_dirty);
INIT_LIST_HEAD(&wb->b_io);
INIT_LIST_HEAD(&wb->b_more_io);
setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
}
int bdi_init(struct backing_dev_info *bdi)
{
int i, err;