From c1955ce32fdb0877b7a1b22feb2669358f65be76 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Sat, 19 Jun 2010 23:08:06 +0200 Subject: writeback: remove wb_list The wb_list member of struct backing_device_info always has exactly one element. Just use the direct bdi->wb pointer instead and simplify some code. Also remove bdi_task_init which is now trivial to prepare for the next patch. Signed-off-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index d5be169..d67989b 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -73,9 +73,9 @@ static void bdi_queue_work(struct backing_dev_info *bdi, * If the default thread isn't there, make sure we add it. When * it gets created and wakes up, we'll run this work. */ - if (unlikely(list_empty_careful(&bdi->wb_list))) + if (unlikely(!bdi->wb.task)) { wake_up_process(default_backing_dev_info.wb.task); - else { + } else { struct bdi_writeback *wb = &bdi->wb; if (wb->task) -- cgit v1.1 From 082439004b31adc146e96e5f1c574dd2b57dcd93 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Sat, 19 Jun 2010 23:08:22 +0200 Subject: writeback: merge bdi_writeback_task and bdi_start_fn Move all code for the writeback thread into fs/fs-writeback.c instead of splitting it over two functions in two files. Signed-off-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index d67989b..c8471b3 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -775,12 +775,36 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait) * Handle writeback of dirty data for the device backed by this bdi. Also * wakes up periodically and does kupdated style flushing. */ -int bdi_writeback_task(struct bdi_writeback *wb) +int bdi_writeback_thread(void *data) { + struct bdi_writeback *wb = data; + struct backing_dev_info *bdi = wb->bdi; unsigned long last_active = jiffies; unsigned long wait_jiffies = -1UL; long pages_written; + /* + * Add us to the active bdi_list + */ + spin_lock_bh(&bdi_lock); + list_add_rcu(&bdi->bdi_list, &bdi_list); + spin_unlock_bh(&bdi_lock); + + current->flags |= PF_FLUSHER | PF_SWAPWRITE; + set_freezable(); + + /* + * Our parent may run at a different priority, just set us to normal + */ + set_user_nice(current, 0); + + /* + * Clear pending bit and wakeup anybody waiting to tear us down + */ + clear_bit(BDI_pending, &bdi->state); + smp_mb__after_clear_bit(); + wake_up_bit(&bdi->state, BDI_pending); + while (!kthread_should_stop()) { pages_written = wb_do_writeback(wb, 0); @@ -813,9 +837,18 @@ int bdi_writeback_task(struct bdi_writeback *wb) try_to_freeze(); } + wb->task = NULL; + + /* + * Flush any work that raced with us exiting. No new work + * will be added, since this bdi isn't discoverable anymore. + */ + if (!list_empty(&bdi->work_list)) + wb_do_writeback(wb, 1); return 0; } + /* * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back * the whole world. -- cgit v1.1 From 455b2864686d3591b3b2f39eb46290c95f76471f Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Wed, 7 Jul 2010 13:24:06 +1000 Subject: writeback: Initial tracing support Trace queue/sched/exec parts of the writeback loop. This provides insight into when and why flusher threads are scheduled to run. e.g a sync invocation leaves traces like: sync-[...]: writeback_queue: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0 flush-8:0-[...]: writeback_exec: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0 This also lays the foundation for adding more writeback tracing to provide deeper insight into the whole writeback path. The original tracing code is from Jens Axboe, though this version is a rewrite as a result of the code being traced changing significantly. Signed-off-by: Dave Chinner Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 38 ++++++++++++++++++++++++++++++-------- 1 file changed, 30 insertions(+), 8 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index c8471b3..73acab4 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -26,15 +26,9 @@ #include #include #include +#include #include "internal.h" -#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info) - -/* - * We don't actually have pdflush, but this one is exported though /proc... - */ -int nr_pdflush_threads; - /* * Passed into wb_writeback(), essentially a subset of writeback_control */ @@ -50,6 +44,21 @@ struct wb_writeback_work { struct completion *done; /* set if the caller waits */ }; +/* + * Include the creation of the trace points after defining the + * wb_writeback_work structure so that the definition remains local to this + * file. + */ +#define CREATE_TRACE_POINTS +#include + +#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info) + +/* + * We don't actually have pdflush, but this one is exported though /proc... + */ +int nr_pdflush_threads; + /** * writeback_in_progress - determine whether there is writeback in progress * @bdi: the device's backing_dev_info structure. @@ -65,6 +74,8 @@ int writeback_in_progress(struct backing_dev_info *bdi) static void bdi_queue_work(struct backing_dev_info *bdi, struct wb_writeback_work *work) { + trace_writeback_queue(bdi, work); + spin_lock(&bdi->wb_lock); list_add_tail(&work->list, &bdi->work_list); spin_unlock(&bdi->wb_lock); @@ -74,6 +85,7 @@ static void bdi_queue_work(struct backing_dev_info *bdi, * it gets created and wakes up, we'll run this work. */ if (unlikely(!bdi->wb.task)) { + trace_writeback_nothread(bdi, work); wake_up_process(default_backing_dev_info.wb.task); } else { struct bdi_writeback *wb = &bdi->wb; @@ -95,8 +107,10 @@ __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages, */ work = kzalloc(sizeof(*work), GFP_ATOMIC); if (!work) { - if (bdi->wb.task) + if (bdi->wb.task) { + trace_writeback_nowork(bdi); wake_up_process(bdi->wb.task); + } return; } @@ -751,6 +765,8 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait) if (force_wait) work->sync_mode = WB_SYNC_ALL; + trace_writeback_exec(bdi, work); + wrote += wb_writeback(wb, work); /* @@ -805,9 +821,13 @@ int bdi_writeback_thread(void *data) smp_mb__after_clear_bit(); wake_up_bit(&bdi->state, BDI_pending); + trace_writeback_thread_start(bdi); + while (!kthread_should_stop()) { pages_written = wb_do_writeback(wb, 0); + trace_writeback_pages_written(pages_written); + if (pages_written) last_active = jiffies; else if (wait_jiffies != -1UL) { @@ -845,6 +865,8 @@ int bdi_writeback_thread(void *data) */ if (!list_empty(&bdi->work_list)) wb_do_writeback(wb, 1); + + trace_writeback_thread_stop(bdi); return 0; } -- cgit v1.1 From 028c2dd184c097809986684f2f0627eea5529fea Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Wed, 7 Jul 2010 13:24:07 +1000 Subject: writeback: Add tracing to balance_dirty_pages Tracing high level background writeback events is good, but it doesn't give the entire picture. Add visibility into write throttling to catch IO dispatched by foreground throttling of processing dirtying lots of pages. Signed-off-by: Dave Chinner Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 73acab4..bf10cbf 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -656,10 +656,14 @@ static long wb_writeback(struct bdi_writeback *wb, wbc.more_io = 0; wbc.nr_to_write = MAX_WRITEBACK_PAGES; wbc.pages_skipped = 0; + + trace_wbc_writeback_start(&wbc, wb->bdi); if (work->sb) __writeback_inodes_sb(work->sb, wb, &wbc); else writeback_inodes_wb(wb, &wbc); + trace_wbc_writeback_written(&wbc, wb->bdi); + work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write; @@ -687,6 +691,7 @@ static long wb_writeback(struct bdi_writeback *wb, if (!list_empty(&wb->b_more_io)) { inode = list_entry(wb->b_more_io.prev, struct inode, i_list); + trace_wbc_writeback_wait(&wbc, wb->bdi); inode_wait_for_writeback(inode); } spin_unlock(&inode_lock); -- cgit v1.1 From 08852b6d6c40f387f2b75e199e2ca1df68970f4c Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Tue, 3 Aug 2010 12:51:16 +0200 Subject: writeback: remove wb in get_next_work_item 83ba7b07 cleans up the writeback. So we don't use wb any more in get_next_work_item. Let's remove unnecessary argument. CC: Christoph Hellwig Signed-off-by: Minchan Kim Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index bf10cbf..261570d 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -704,7 +704,7 @@ static long wb_writeback(struct bdi_writeback *wb, * Return the next wb_writeback_work struct that hasn't been processed yet. */ static struct wb_writeback_work * -get_next_work_item(struct backing_dev_info *bdi, struct bdi_writeback *wb) +get_next_work_item(struct backing_dev_info *bdi) { struct wb_writeback_work *work = NULL; @@ -762,7 +762,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait) struct wb_writeback_work *work; long wrote = 0; - while ((work = get_next_work_item(bdi, wb)) != NULL) { + while ((work = get_next_work_item(bdi)) != NULL) { /* * Override sync mode, in case we must wait for completion * because this thread is exiting now. -- cgit v1.1 From 6f904ff0e39ea88f81eb77e8dfb4e1238492f0a8 Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:11 +0300 Subject: writeback: harmonize writeback threads naming The write-back code mixes words "thread" and "task" for the same things. This is not a big deal, but still an inconsistency. hch: a convention I tend to use and I've seen in various places is to always use _task for the storage of the task_struct pointer, and thread everywhere else. This especially helps with having foo_thread for the actual thread and foo_task for a global variable keeping the task_struct pointer This patch renames: * 'bdi_add_default_flusher_task()' -> 'bdi_add_default_flusher_thread()' * 'bdi_forker_task()' -> 'bdi_forker_thread()' because bdi threads are 'bdi_writeback_thread()', so these names are more consistent. This patch also amends commentaries and makes them refer the forker and bdi threads as "thread", not "task". Also, while on it, make 'bdi_add_default_flusher_thread()' declaration use 'static void' instead of 'void static' and make checkpatch.pl happy. Signed-off-by: Artem Bityutskiy Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 261570d..002be0f 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -840,7 +840,7 @@ int bdi_writeback_thread(void *data) /* * Longest period of inactivity that we tolerate. If we - * see dirty data again later, the task will get + * see dirty data again later, the thread will get * recreated automatically. */ max_idle = max(5UL * 60 * HZ, wait_jiffies); -- cgit v1.1 From 297252c81de8043ca6c36e5984c24fdb5aab9013 Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:15 +0300 Subject: writeback: do not lose wake-ups in bdi threads Currently, bdi threads ('bdi_writeback_thread()') can lose wake-ups. For example, if 'bdi_queue_work()' is executed after the bdi thread have had finished 'wb_do_writeback()' but before it called 'schedule_timeout_interruptible()'. To fix this issue, we have to check whether we have works to process after we have changed the task state to 'TASK_INTERRUPTIBLE'. This patch also clean-ups handling of the cases when 'dirty_writeback_interval' is zero or non-zero. Additionally, this patch also removes unneeded 'list_empty_careful()' call. Signed-off-by: Artem Bityutskiy Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 002be0f..05444ea 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -848,17 +848,18 @@ int bdi_writeback_thread(void *data) break; } - if (dirty_writeback_interval) { - wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10); - schedule_timeout_interruptible(wait_jiffies); - } else { - set_current_state(TASK_INTERRUPTIBLE); - if (list_empty_careful(&wb->bdi->work_list) && - !kthread_should_stop()) - schedule(); + set_current_state(TASK_INTERRUPTIBLE); + if (!list_empty(&bdi->work_list)) { __set_current_state(TASK_RUNNING); + continue; } + if (dirty_writeback_interval) { + wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10); + schedule_timeout(wait_jiffies); + } else + schedule(); + try_to_freeze(); } -- cgit v1.1 From 78c40cb6581a74adc48821f3de6b864a54d4c34d Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:17 +0300 Subject: writeback: do not remove bdi from bdi_list The forker thread removes bdis from 'bdi_list' before forking the bdi thread. But this is wrong for at least 2 reasons. Reason #1: if we temporary remove a bdi from the list, we may miss works which would otherwise be given to us. Reason #2: this is racy; indeed, 'bdi_wb_shutdown()' expects that bdis are always in the 'bdi_list' (see 'bdi_remove_from_list()'), and when it races with the forker thread, it can shut down the bdi thread at the same time as the forker creates it. This patch makes sure the forker thread never removes bdis from 'bdi_list' (which was suggested by Christoph Hellwig). In order to make sure that we do not race with 'bdi_wb_shutdown()', we have to hold the 'bdi_lock' while walking the 'bdi_list' and setting the 'BDI_pending' flag. NOTE! The error path is interesting. Currently, when we fail to create a bdi thread, we move the bdi to the tail of 'bdi_list'. But if we never remove the bdi from the list, we cannot move it to the tail either, because then we can mess up the RCU readers which walk the list. And also, we'll have the race described above in "Reason #2". But I not think that adding to the tail is any important so I just do not do that. Signed-off-by: Artem Bityutskiy Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 7 ------- 1 file changed, 7 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 05444ea..57fbfd0 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -804,13 +804,6 @@ int bdi_writeback_thread(void *data) unsigned long wait_jiffies = -1UL; long pages_written; - /* - * Add us to the active bdi_list - */ - spin_lock_bh(&bdi_lock); - list_add_rcu(&bdi->bdi_list, &bdi_list); - spin_unlock_bh(&bdi_lock); - current->flags |= PF_FLUSHER | PF_SWAPWRITE; set_freezable(); -- cgit v1.1 From ecd584030da67ede1bf17955746a6ce834d9fc6b Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:18 +0300 Subject: writeback: move last_active to bdi Currently bdi threads use local variable 'last_active' which stores last time when the bdi thread did some useful work. Move this local variable to 'struct bdi_writeback'. This is just a preparation for the further patches which will make the forker thread decide when bdi threads should be killed. Signed-off-by: Artem Bityutskiy Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 57fbfd0..9f5cab7 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -800,12 +800,12 @@ int bdi_writeback_thread(void *data) { struct bdi_writeback *wb = data; struct backing_dev_info *bdi = wb->bdi; - unsigned long last_active = jiffies; unsigned long wait_jiffies = -1UL; long pages_written; current->flags |= PF_FLUSHER | PF_SWAPWRITE; set_freezable(); + wb->last_active = jiffies; /* * Our parent may run at a different priority, just set us to normal @@ -827,7 +827,7 @@ int bdi_writeback_thread(void *data) trace_writeback_pages_written(pages_written); if (pages_written) - last_active = jiffies; + wb->last_active = jiffies; else if (wait_jiffies != -1UL) { unsigned long max_idle; @@ -837,7 +837,7 @@ int bdi_writeback_thread(void *data) * recreated automatically. */ max_idle = max(5UL * 60 * HZ, wait_jiffies); - if (time_after(jiffies, max_idle + last_active)) + if (time_after(jiffies, max_idle + wb->last_active)) break; } -- cgit v1.1 From fff5b85aa4225a7be157f208277a055822039a9e Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:20 +0300 Subject: writeback: move bdi threads exiting logic to the forker thread Currently, bdi threads can decide to exit if there were no useful activities for 5 minutes. However, this causes nasty races: we can easily oops in the 'bdi_queue_work()' if the bdi thread decides to exit while we are waking it up. And even if we do not oops, but the bdi tread exits immediately after we wake it up, we'd lose the wake-up event and have an unnecessary delay (up to 5 secs) in the bdi work processing. This patch makes the forker thread to be the central place which not only creates bdi threads, but also kills them if they were inactive long enough. This better design-wise. Another reason why this change was done is to prepare for the further changes which will prevent the bdi threads from waking up every 5 sec and wasting power. Indeed, when the task does not wake up periodically anymore, it won't be able to exit either. This patch also moves the the 'wake_up_bit()' call from the bdi thread to the forker thread as well. So now the forker thread sets the BDI_pending bit, then forks the task or kills it, then clears the bit and wakes up the waiting process. The only process which may wain on the bit is 'bdi_wb_shutdown()'. This function was changed as well - now it first removes the bdi from the 'bdi_list', then waits on the 'BDI_pending' bit. Once it wakes up, it is guaranteed that the forker thread won't race with it, because the bdi is not visible. Note, the forker thread sets the 'BDI_pending' bit under the 'bdi->wb_lock' which is essential for proper serialization. And additionally, when we change 'bdi->wb.task', we now take the 'bdi->work_lock', to make sure that we do not lose wake-ups which we otherwise would when raced with, say, 'bdi_queue_work()'. Signed-off-by: Artem Bityutskiy Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 54 ++++++++++++------------------------------------------ 1 file changed, 12 insertions(+), 42 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 9f5cab7..905f3ea 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -78,21 +78,17 @@ static void bdi_queue_work(struct backing_dev_info *bdi, spin_lock(&bdi->wb_lock); list_add_tail(&work->list, &bdi->work_list); - spin_unlock(&bdi->wb_lock); - - /* - * If the default thread isn't there, make sure we add it. When - * it gets created and wakes up, we'll run this work. - */ - if (unlikely(!bdi->wb.task)) { + if (bdi->wb.task) { + wake_up_process(bdi->wb.task); + } else { + /* + * The bdi thread isn't there, wake up the forker thread which + * will create and run it. + */ trace_writeback_nothread(bdi, work); wake_up_process(default_backing_dev_info.wb.task); - } else { - struct bdi_writeback *wb = &bdi->wb; - - if (wb->task) - wake_up_process(wb->task); } + spin_unlock(&bdi->wb_lock); } static void @@ -800,7 +796,6 @@ int bdi_writeback_thread(void *data) { struct bdi_writeback *wb = data; struct backing_dev_info *bdi = wb->bdi; - unsigned long wait_jiffies = -1UL; long pages_written; current->flags |= PF_FLUSHER | PF_SWAPWRITE; @@ -812,13 +807,6 @@ int bdi_writeback_thread(void *data) */ set_user_nice(current, 0); - /* - * Clear pending bit and wakeup anybody waiting to tear us down - */ - clear_bit(BDI_pending, &bdi->state); - smp_mb__after_clear_bit(); - wake_up_bit(&bdi->state, BDI_pending); - trace_writeback_thread_start(bdi); while (!kthread_should_stop()) { @@ -828,18 +816,6 @@ int bdi_writeback_thread(void *data) if (pages_written) wb->last_active = jiffies; - else if (wait_jiffies != -1UL) { - unsigned long max_idle; - - /* - * Longest period of inactivity that we tolerate. If we - * see dirty data again later, the thread will get - * recreated automatically. - */ - max_idle = max(5UL * 60 * HZ, wait_jiffies); - if (time_after(jiffies, max_idle + wb->last_active)) - break; - } set_current_state(TASK_INTERRUPTIBLE); if (!list_empty(&bdi->work_list)) { @@ -847,21 +823,15 @@ int bdi_writeback_thread(void *data) continue; } - if (dirty_writeback_interval) { - wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10); - schedule_timeout(wait_jiffies); - } else + if (dirty_writeback_interval) + schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10)); + else schedule(); try_to_freeze(); } - wb->task = NULL; - - /* - * Flush any work that raced with us exiting. No new work - * will be added, since this bdi isn't discoverable anymore. - */ + /* Flush any work that raced with us exiting */ if (!list_empty(&bdi->work_list)) wb_do_writeback(wb, 1); -- cgit v1.1 From 253c34e9b10c30d3064be654b5b78fbc1a8b1896 Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:21 +0300 Subject: writeback: prevent unnecessary bdi threads wakeups Finally, we can get rid of unnecessary wake-ups in bdi threads, which are very bad for battery-driven devices. There are two types of activities bdi threads do: 1. process bdi works from the 'bdi->work_list' 2. periodic write-back So there are 2 sources of wake-up events for bdi threads: 1. 'bdi_queue_work()' - submits bdi works 2. '__mark_inode_dirty()' - adds dirty I/O to bdi's The former already has bdi wake-up code. The latter does not, and this patch adds it. '__mark_inode_dirty()' is hot-path function, but this patch adds another 'spin_lock(&bdi->wb_lock)' there. However, it is taken only in rare cases when the bdi has no dirty inodes. So adding this spinlock should be fine and should not affect performance. This patch makes sure bdi threads and the forker thread do not wake-up if there is nothing to do. The forker thread will nevertheless wake up at least every 5 min. to check whether it has to kill a bdi thread. This can also be optimized, but is not worth it. This patch also tidies up the warning about unregistered bid, and turns it from an ugly crocodile to a simple 'WARN()' statement. Signed-off-by: Artem Bityutskiy Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 59 ++++++++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 48 insertions(+), 11 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 905f3ea..55f6e46 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -823,10 +823,16 @@ int bdi_writeback_thread(void *data) continue; } - if (dirty_writeback_interval) + if (wb_has_dirty_io(wb) && dirty_writeback_interval) schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10)); - else + else { + /* + * We have nothing to do, so can go sleep without any + * timeout and save power. When a work is queued or + * something is made dirty - we will be woken up. + */ schedule(); + } try_to_freeze(); } @@ -862,6 +868,26 @@ 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")) { @@ -914,6 +940,8 @@ static noinline void block_dump___mark_inode_dirty(struct inode *inode) void __mark_inode_dirty(struct inode *inode, int flags) { struct super_block *sb = inode->i_sb; + struct backing_dev_info *bdi = NULL; + bool wakeup_bdi = false; /* * Don't do this for I_DIRTY_PAGES - that doesn't actually @@ -967,22 +995,31 @@ void __mark_inode_dirty(struct inode *inode, int flags) * reposition it (that would break b_dirty time-ordering). */ if (!was_dirty) { - struct bdi_writeback *wb = &inode_to_bdi(inode)->wb; - struct backing_dev_info *bdi = wb->bdi; - - if (bdi_cap_writeback_dirty(bdi) && - !test_bit(BDI_registered, &bdi->state)) { - WARN_ON(1); - printk(KERN_ERR "bdi-%s not registered\n", - bdi->name); + bdi = inode_to_bdi(inode); + + if (bdi_cap_writeback_dirty(bdi)) { + WARN(!test_bit(BDI_registered, &bdi->state), + "bdi-%s not registered\n", bdi->name); + + /* + * If this is the first dirty inode for this + * bdi, we have to wake-up the corresponding + * bdi thread to make sure background + * write-back happens later. + */ + if (!wb_has_dirty_io(&bdi->wb)) + wakeup_bdi = true; } inode->dirtied_when = jiffies; - list_move(&inode->i_list, &wb->b_dirty); + list_move(&inode->i_list, &bdi->wb.b_dirty); } } out: spin_unlock(&inode_lock); + + if (wakeup_bdi) + wakeup_bdi_thread(bdi); } EXPORT_SYMBOL(__mark_inode_dirty); -- cgit v1.1 From 6467716a37673e8d47b4984eb19839bdad0a8353 Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:22 +0300 Subject: 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 Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 36 +++++++++++------------------------- 1 file changed, 11 insertions(+), 25 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 55f6e46..bfa2df2 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -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); -- cgit v1.1 From a4ffdde6e56fdf8c34ddadc2674d6eb978083369 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Wed, 2 Jun 2010 17:38:30 -0400 Subject: simplify checks for I_CLEAR/I_FREEING add I_CLEAR instead of replacing I_FREEING with it. I_CLEAR is equivalent to I_FREEING for almost all code looking at either; it's there to keep track of having called clear_inode() exactly once per inode lifetime, at some point after having set I_FREEING. I_CLEAR and I_FREEING never get set at the same time with the current code, so we can switch to setting i_flags to I_FREEING | I_CLEAR instead of I_CLEAR without loss of information. As the result of such change, checks become simpler and the amount of code that needs to know about I_CLEAR shrinks a lot. Signed-off-by: Al Viro --- fs/fs-writeback.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index d5be169..7608880 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -352,7 +352,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc) spin_lock(&inode_lock); inode->i_state &= ~I_SYNC; - if (!(inode->i_state & (I_FREEING | I_CLEAR))) { + if (!(inode->i_state & I_FREEING)) { if ((inode->i_state & I_DIRTY_PAGES) && wbc->for_kupdate) { /* * More pages get dirtied by a fast dirtier. @@ -499,7 +499,7 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb, if (inode_dirtied_after(inode, wbc->wb_start)) return 1; - BUG_ON(inode->i_state & (I_FREEING | I_CLEAR)); + BUG_ON(inode->i_state & I_FREEING); __iget(inode); pages_skipped = wbc->pages_skipped; writeback_single_inode(inode, wbc); @@ -935,7 +935,7 @@ void __mark_inode_dirty(struct inode *inode, int flags) if (hlist_unhashed(&inode->i_hash)) goto out; } - if (inode->i_state & (I_FREEING|I_CLEAR)) + if (inode->i_state & I_FREEING) goto out; /* @@ -1001,7 +1001,7 @@ static void wait_sb_inodes(struct super_block *sb) list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { struct address_space *mapping; - if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW)) + if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) continue; mapping = inode->i_mapping; if (mapping->nrpages == 0) -- cgit v1.1