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 --- include/linux/backing-dev.h | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'include/linux/backing-dev.h') diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index e9aec0d099df..50f146146169 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -45,8 +45,6 @@ enum bdi_stat_item { #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids))) struct bdi_writeback { - struct list_head list; /* hangs off the bdi */ - struct backing_dev_info *bdi; /* our parent bdi */ unsigned int nr; @@ -80,8 +78,7 @@ struct backing_dev_info { unsigned int max_ratio, max_prop_frac; struct bdi_writeback wb; /* default writeback info for this bdi */ - spinlock_t wb_lock; /* protects update side of wb_list */ - struct list_head wb_list; /* the flusher threads hanging off this bdi */ + spinlock_t wb_lock; /* protects work_list */ struct list_head work_list; -- cgit v1.2.3 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 --- include/linux/backing-dev.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/backing-dev.h') diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index 50f146146169..e536f3a74e60 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -102,7 +102,7 @@ void bdi_unregister(struct backing_dev_info *bdi); int bdi_setup_and_register(struct backing_dev_info *, char *, unsigned int); void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages); void bdi_start_background_writeback(struct backing_dev_info *bdi); -int bdi_writeback_task(struct bdi_writeback *wb); +int bdi_writeback_thread(void *data); int bdi_has_dirty_io(struct backing_dev_info *bdi); void bdi_arm_supers_timer(void); -- cgit v1.2.3 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 --- include/linux/backing-dev.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/backing-dev.h') diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index e536f3a74e60..f0936f5f85dd 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -50,7 +50,7 @@ struct bdi_writeback { unsigned long last_old_flush; /* last old data flush */ - struct task_struct *task; /* writeback task */ + struct task_struct *task; /* writeback thread */ 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 */ -- cgit v1.2.3 From 080dcec41709be72613133f695be75b98dd43e88 Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 25 Jul 2010 14:29:16 +0300 Subject: writeback: simplify bdi code a little This patch simplifies bdi code a little by removing the 'pending_list' which is redundant. Indeed, currently the forker thread ('bdi_forker_thread()') is working like this: 1. In a loop, fetch all bdi's which have works but have no writeback thread and move them to the 'pending_list'. 2. If the list is empty, sleep for 5 sec. 3. Otherwise, take one bdi from the list, fork the writeback thread for this bdi, and repeat the loop. IOW, it first moves everything to the 'pending_list', then process only one element, and so on. This patch simplifies the algorithm, which is now as follows. 1. Find the first bdi which has a work and remove it from the global list of bdi's (bdi_list). 2. If there was not such bdi, sleep 5 sec. 3. Fork the writeback thread for this bdi and repeat the loop. IOW, now we find the first bdi to process, process it, and so on. This is simpler and involves less lists. The bonus now is that we can get rid of a couple of functions, as well as remove complications which involve 'rcu_call()' and 'bdi->rcu_head'. This patch also makes sure we use 'list_add_tail_rcu()', instead of plain 'list_add_tail()', but this piece of code is going to be removed in the next patch anyway. Signed-off-by: Artem Bityutskiy Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- include/linux/backing-dev.h | 1 - 1 file changed, 1 deletion(-) (limited to 'include/linux/backing-dev.h') diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index f0936f5f85dd..95ecb2bebca8 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -58,7 +58,6 @@ struct bdi_writeback { struct backing_dev_info { struct list_head bdi_list; - struct rcu_head rcu_head; unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */ unsigned long state; /* Always use atomic bitops on this */ unsigned int capabilities; /* Device capabilities */ -- cgit v1.2.3 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 --- include/linux/backing-dev.h | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'include/linux/backing-dev.h') diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index 95ecb2bebca8..71b6223e0a77 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -45,15 +45,16 @@ enum bdi_stat_item { #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids))) struct bdi_writeback { - struct backing_dev_info *bdi; /* our parent bdi */ + struct backing_dev_info *bdi; /* our parent bdi */ unsigned int nr; - unsigned long last_old_flush; /* last old data flush */ + unsigned long last_old_flush; /* last old data flush */ + unsigned long last_active; /* last time bdi thread was active */ - struct task_struct *task; /* writeback thread */ - 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 */ + struct task_struct *task; /* writeback thread */ + 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 */ }; struct backing_dev_info { -- cgit v1.2.3 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 --- include/linux/backing-dev.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux/backing-dev.h') diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index 71b6223e0a77..7628219e5386 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -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; -- cgit v1.2.3 From 81d73a32d775ae9674ea6edf0b5b721fc3bc57d9 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 11 Aug 2010 14:17:44 -0700 Subject: mm: fix writeback_in_progress() Commit 83ba7b071f3 ("writeback: simplify the write back thread queue") broke writeback_in_progress() as in that commit we started to remove work items from the list at the moment we start working on them and not at the moment they are finished. Thus if the flusher thread was doing some work but there was no other work queued, writeback_in_progress() returned false. This could in particular cause unnecessary queueing of background writeback from balance_dirty_pages() or writeout work from writeback_sb_if_idle(). This patch fixes the problem by introducing a bit in the bdi state which indicates that the flusher thread is processing some work and uses this bit for writeback_in_progress() test. NOTE: Both callsites of writeback_in_progress() (namely, writeback_inodes_sb_if_idle() and balance_dirty_pages()) would actually need a different information than what writeback_in_progress() provides. They would need to know whether *the kind of writeback they are going to submit* is already queued. But this information isn't that simple to provide so let's fix writeback_in_progress() for the time being. Signed-off-by: Jan Kara Cc: Christoph Hellwig Cc: Wu Fengguang Acked-by: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/backing-dev.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/backing-dev.h') diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index 7628219e5386..35b00746c712 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -31,6 +31,7 @@ enum bdi_state { BDI_async_congested, /* The async (write) queue is getting full */ BDI_sync_congested, /* The sync queue is getting full */ BDI_registered, /* bdi_register() was done */ + BDI_writeback_running, /* Writeback is in progress */ BDI_unused, /* Available bits start here */ }; -- cgit v1.2.3