Re: [PATCH 04/10] writeback: move backing_dev_info->wb_lock and ->worklist into bdi_writeback
From: Jan Kara
Date: Thu Nov 20 2014 - 11:01:37 EST
On Tue 18-11-14 03:37:22, Tejun Heo wrote:
> Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
> and the role of the separation is unclear. For cgroup support for
> writeback IOs, a bdi will be updated to host multiple wb's where each
> wb serves writeback IOs of a different cgroup on the bdi. To achieve
> that, a wb should carry all states necessary for servicing writeback
> IOs for a cgroup independently.
>
> This patch moves bdi->wb_lock and ->worklist into wb.
>
> * The lock protects bdi->worklist and bdi->wb.dwork scheduling. While
> moving, rename it to wb->work_lock as wb->wb_lock is confusing.
> Also, move wb->dwork downwards so that it's colocated with the new
> ->work_lock and ->work_list fields.
>
> * bdi_writeback_workfn() -> wb_workfn()
> bdi_wakeup_thread_delayed(bdi) -> wb_wakeup_delayed(wb)
> bdi_wakeup_thread(bdi) -> wb_wakeup(wb)
> bdi_queue_work(bdi, ...) -> wb_queue_work(wb, ...)
> __bdi_start_writeback(bdi, ...) -> __wb_start_writeback(wb, ...)
> get_next_work_item(bdi) -> get_next_work_item(wb)
>
> * bdi_wb_shutdown() is renamed to wb_shutdown() and now takes @wb.
> The function contained parts which belong to the containing bdi
> rather than the wb itself - testing cap_writeback_dirty and
> bdi_remove_from_list() invocation. Those are moved to
> bdi_unregister().
>
> * bdi_wb_{init|exit}() are renamed to wb_{init|exit}().
> Initializations of the moved bdi->wb_lock and ->work_list are
> relocated from bdi_init() to wb_init().
>
> * As there's still only one bdi_writeback per backing_dev_info, all
> uses of bdi->state are mechanically replaced with bdi->wb.state
> introducing no behavior changes.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Does this mean you want to have per-device, per-cgroup flusher workqueues?
Otherwise this change doesn't make sense...
Honza
> ---
> fs/fs-writeback.c | 84 +++++++++++++++++++++------------------------
> include/linux/backing-dev.h | 12 +++----
> mm/backing-dev.c | 64 +++++++++++++++++-----------------
> 3 files changed, 77 insertions(+), 83 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index daa91ae..41c9f1e 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -91,34 +91,33 @@ static inline struct inode *wb_inode(struct list_head *head)
>
> EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
>
> -static void bdi_wakeup_thread(struct backing_dev_info *bdi)
> +static void wb_wakeup(struct bdi_writeback *wb)
> {
> - spin_lock_bh(&bdi->wb_lock);
> - if (test_bit(WB_registered, &bdi->wb.state))
> - mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
> - spin_unlock_bh(&bdi->wb_lock);
> + spin_lock_bh(&wb->work_lock);
> + if (test_bit(WB_registered, &wb->state))
> + mod_delayed_work(bdi_wq, &wb->dwork, 0);
> + spin_unlock_bh(&wb->work_lock);
> }
> -static void bdi_queue_work(struct backing_dev_info *bdi,
> - struct wb_writeback_work *work)
> +static void wb_queue_work(struct bdi_writeback *wb,
> + struct wb_writeback_work *work)
> {
> - trace_writeback_queue(bdi, work);
> + trace_writeback_queue(wb->bdi, work);
>
> - spin_lock_bh(&bdi->wb_lock);
> - if (!test_bit(WB_registered, &bdi->wb.state)) {
> + spin_lock_bh(&wb->work_lock);
> + if (!test_bit(WB_registered, &wb->state)) {
> if (work->done)
> complete(work->done);
> goto out_unlock;
> }
> - list_add_tail(&work->list, &bdi->work_list);
> - mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
> + list_add_tail(&work->list, &wb->work_list);
> + mod_delayed_work(bdi_wq, &wb->dwork, 0);
> out_unlock:
> - spin_unlock_bh(&bdi->wb_lock);
> + spin_unlock_bh(&wb->work_lock);
> }
>
> -static void
> -__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
> - bool range_cyclic, enum wb_reason reason)
> +static void __wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
> + bool range_cyclic, enum wb_reason reason)
> {
> struct wb_writeback_work *work;
>
> @@ -128,8 +127,8 @@ __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
> */
> work = kzalloc(sizeof(*work), GFP_ATOMIC);
> if (!work) {
> - trace_writeback_nowork(bdi);
> - bdi_wakeup_thread(bdi);
> + trace_writeback_nowork(wb->bdi);
> + wb_wakeup(wb);
> return;
> }
>
> @@ -138,7 +137,7 @@ __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
> work->range_cyclic = range_cyclic;
> work->reason = reason;
>
> - bdi_queue_work(bdi, work);
> + wb_queue_work(wb, work);
> }
>
> /**
> @@ -156,7 +155,7 @@ __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
> void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
> enum wb_reason reason)
> {
> - __bdi_start_writeback(bdi, nr_pages, true, reason);
> + __wb_start_writeback(&bdi->wb, nr_pages, true, reason);
> }
>
> /**
> @@ -176,7 +175,7 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi)
> * writeback as soon as there is no other work to do.
> */
> trace_writeback_wake_background(bdi);
> - bdi_wakeup_thread(bdi);
> + wb_wakeup(&bdi->wb);
> }
>
> /*
> @@ -848,7 +847,7 @@ static long wb_writeback(struct bdi_writeback *wb,
> * after the other works are all done.
> */
> if ((work->for_background || work->for_kupdate) &&
> - !list_empty(&wb->bdi->work_list))
> + !list_empty(&wb->work_list))
> break;
>
> /*
> @@ -919,18 +918,17 @@ 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)
> +static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
> {
> struct wb_writeback_work *work = NULL;
>
> - spin_lock_bh(&bdi->wb_lock);
> - if (!list_empty(&bdi->work_list)) {
> - work = list_entry(bdi->work_list.next,
> + spin_lock_bh(&wb->work_lock);
> + if (!list_empty(&wb->work_list)) {
> + work = list_entry(wb->work_list.next,
> struct wb_writeback_work, list);
> list_del_init(&work->list);
> }
> - spin_unlock_bh(&bdi->wb_lock);
> + spin_unlock_bh(&wb->work_lock);
> return work;
> }
>
> @@ -1002,14 +1000,13 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
> */
> static long wb_do_writeback(struct bdi_writeback *wb)
> {
> - struct backing_dev_info *bdi = wb->bdi;
> struct wb_writeback_work *work;
> long wrote = 0;
>
> set_bit(WB_writeback_running, &wb->state);
> - while ((work = get_next_work_item(bdi)) != NULL) {
> + while ((work = get_next_work_item(wb)) != NULL) {
>
> - trace_writeback_exec(bdi, work);
> + trace_writeback_exec(wb->bdi, work);
>
> wrote += wb_writeback(wb, work);
>
> @@ -1037,43 +1034,42 @@ static long wb_do_writeback(struct bdi_writeback *wb)
> * Handle writeback of dirty data for the device backed by this bdi. Also
> * reschedules periodically and does kupdated style flushing.
> */
> -void bdi_writeback_workfn(struct work_struct *work)
> +void wb_workfn(struct work_struct *work)
> {
> struct bdi_writeback *wb = container_of(to_delayed_work(work),
> struct bdi_writeback, dwork);
> - struct backing_dev_info *bdi = wb->bdi;
> long pages_written;
>
> - set_worker_desc("flush-%s", dev_name(bdi->dev));
> + set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
> current->flags |= PF_SWAPWRITE;
>
> if (likely(!current_is_workqueue_rescuer() ||
> !test_bit(WB_registered, &wb->state))) {
> /*
> - * The normal path. Keep writing back @bdi until its
> + * The normal path. Keep writing back @wb until its
> * work_list is empty. Note that this path is also taken
> - * if @bdi is shutting down even when we're running off the
> + * if @wb is shutting down even when we're running off the
> * rescuer as work_list needs to be drained.
> */
> do {
> pages_written = wb_do_writeback(wb);
> trace_writeback_pages_written(pages_written);
> - } while (!list_empty(&bdi->work_list));
> + } while (!list_empty(&wb->work_list));
> } else {
> /*
> * bdi_wq can't get enough workers and we're running off
> * the emergency worker. Don't hog it. Hopefully, 1024 is
> * enough for efficient IO.
> */
> - pages_written = writeback_inodes_wb(&bdi->wb, 1024,
> + pages_written = writeback_inodes_wb(wb, 1024,
> WB_REASON_FORKER_THREAD);
> trace_writeback_pages_written(pages_written);
> }
>
> - if (!list_empty(&bdi->work_list))
> + if (!list_empty(&wb->work_list))
> mod_delayed_work(bdi_wq, &wb->dwork, 0);
> else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
> - bdi_wakeup_thread_delayed(bdi);
> + wb_wakeup_delayed(wb);
>
> current->flags &= ~PF_SWAPWRITE;
> }
> @@ -1093,7 +1089,7 @@ void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
> list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
> if (!bdi_has_dirty_io(bdi))
> continue;
> - __bdi_start_writeback(bdi, nr_pages, false, reason);
> + __wb_start_writeback(&bdi->wb, nr_pages, false, reason);
> }
> rcu_read_unlock();
> }
> @@ -1228,7 +1224,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> spin_unlock(&bdi->wb.list_lock);
>
> if (wakeup_bdi)
> - bdi_wakeup_thread_delayed(bdi);
> + wb_wakeup_delayed(&bdi->wb);
> return;
> }
> }
> @@ -1318,7 +1314,7 @@ void writeback_inodes_sb_nr(struct super_block *sb,
> if (sb->s_bdi == &noop_backing_dev_info)
> return;
> WARN_ON(!rwsem_is_locked(&sb->s_umount));
> - bdi_queue_work(sb->s_bdi, &work);
> + wb_queue_work(&sb->s_bdi->wb, &work);
> wait_for_completion(&done);
> }
> EXPORT_SYMBOL(writeback_inodes_sb_nr);
> @@ -1402,7 +1398,7 @@ void sync_inodes_sb(struct super_block *sb)
> return;
> WARN_ON(!rwsem_is_locked(&sb->s_umount));
>
> - bdi_queue_work(sb->s_bdi, &work);
> + wb_queue_work(&sb->s_bdi->wb, &work);
> wait_for_completion(&done);
>
> wait_sb_inodes(sb);
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index a077a8d..6aba0d3 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -52,7 +52,6 @@ struct bdi_writeback {
> unsigned long state; /* Always use atomic bitops on this */
> unsigned long last_old_flush; /* last old data flush */
>
> - struct delayed_work dwork; /* work item used for writeback */
> 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 */
> @@ -77,6 +76,10 @@ struct bdi_writeback {
>
> struct fprop_local_percpu completions;
> int dirty_exceeded;
> +
> + spinlock_t work_lock; /* protects work_list & dwork scheduling */
> + struct list_head work_list;
> + struct delayed_work dwork; /* work item used for writeback */
> };
>
> struct backing_dev_info {
> @@ -92,9 +95,6 @@ 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 work_list & wb.dwork scheduling */
> -
> - struct list_head work_list;
>
> struct device *dev;
>
> @@ -118,9 +118,9 @@ int __must_check bdi_setup_and_register(struct backing_dev_info *, char *, unsig
> void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
> enum wb_reason reason);
> void bdi_start_background_writeback(struct backing_dev_info *bdi);
> -void bdi_writeback_workfn(struct work_struct *work);
> +void wb_workfn(struct work_struct *work);
> int bdi_has_dirty_io(struct backing_dev_info *bdi);
> -void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi);
> +void wb_wakeup_delayed(struct bdi_writeback *wb);
>
> extern spinlock_t bdi_lock;
> extern struct list_head bdi_list;
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 7b9b10e..4904456 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -278,7 +278,7 @@ int bdi_has_dirty_io(struct backing_dev_info *bdi)
> }
>
> /*
> - * This function is used when the first inode for this bdi is marked dirty. It
> + * This function is used when the first inode for this wb 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
> @@ -291,15 +291,15 @@ int bdi_has_dirty_io(struct backing_dev_info *bdi)
> * We have to be careful not to postpone flush work if it is scheduled for
> * earlier. Thus we use queue_delayed_work().
> */
> -void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
> +void wb_wakeup_delayed(struct bdi_writeback *wb)
> {
> unsigned long timeout;
>
> timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> - spin_lock_bh(&bdi->wb_lock);
> - if (test_bit(WB_registered, &bdi->wb.state))
> - queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
> - spin_unlock_bh(&bdi->wb_lock);
> + spin_lock_bh(&wb->work_lock);
> + if (test_bit(WB_registered, &wb->state))
> + queue_delayed_work(bdi_wq, &wb->dwork, timeout);
> + spin_unlock_bh(&wb->work_lock);
> }
>
> /*
> @@ -352,30 +352,22 @@ EXPORT_SYMBOL(bdi_register_dev);
> /*
> * Remove bdi from the global list and shutdown any threads we have running
> */
> -static void bdi_wb_shutdown(struct backing_dev_info *bdi)
> +static void wb_shutdown(struct bdi_writeback *wb)
> {
> - if (!bdi_cap_writeback_dirty(bdi))
> - return;
> -
> - /*
> - * Make sure nobody finds us on the bdi_list anymore
> - */
> - bdi_remove_from_list(bdi);
> -
> /* Make sure nobody queues further work */
> - spin_lock_bh(&bdi->wb_lock);
> - clear_bit(WB_registered, &bdi->wb.state);
> - spin_unlock_bh(&bdi->wb_lock);
> + spin_lock_bh(&wb->work_lock);
> + clear_bit(WB_registered, &wb->state);
> + spin_unlock_bh(&wb->work_lock);
>
> /*
> - * Drain work list and shutdown the delayed_work. At this point,
> - * @bdi->bdi_list is empty telling bdi_Writeback_workfn() that @bdi
> - * is dying and its work_list needs to be drained no matter what.
> + * Drain work list and shutdown the delayed_work. !WB_registered
> + * tells wb_workfn() that @wb is dying and its work_list needs to
> + * be drained no matter what.
> */
> - mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
> - flush_delayed_work(&bdi->wb.dwork);
> - WARN_ON(!list_empty(&bdi->work_list));
> - WARN_ON(delayed_work_pending(&bdi->wb.dwork));
> + mod_delayed_work(bdi_wq, &wb->dwork, 0);
> + flush_delayed_work(&wb->dwork);
> + WARN_ON(!list_empty(&wb->work_list));
> + WARN_ON(delayed_work_pending(&wb->dwork));
> }
>
> /*
> @@ -400,7 +392,12 @@ void bdi_unregister(struct backing_dev_info *bdi)
> trace_writeback_bdi_unregister(bdi);
> bdi_prune_sb(bdi);
>
> - bdi_wb_shutdown(bdi);
> + if (bdi_cap_writeback_dirty(bdi)) {
> + /* make sure nobody finds us on the bdi_list anymore */
> + bdi_remove_from_list(bdi);
> + wb_shutdown(&bdi->wb);
> + }
> +
> bdi_debug_unregister(bdi);
> device_unregister(bdi->dev);
> bdi->dev = NULL;
> @@ -413,7 +410,7 @@ EXPORT_SYMBOL(bdi_unregister);
> */
> #define INIT_BW (100 << (20 - PAGE_SHIFT))
>
> -static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
> +static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
> {
> int i, err;
>
> @@ -425,7 +422,6 @@ static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
> INIT_LIST_HEAD(&wb->b_io);
> INIT_LIST_HEAD(&wb->b_more_io);
> spin_lock_init(&wb->list_lock);
> - INIT_DELAYED_WORK(&wb->dwork, bdi_writeback_workfn);
>
> wb->bw_time_stamp = jiffies;
> wb->balanced_dirty_ratelimit = INIT_BW;
> @@ -433,6 +429,10 @@ static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
> wb->write_bandwidth = INIT_BW;
> wb->avg_write_bandwidth = INIT_BW;
>
> + spin_lock_init(&wb->work_lock);
> + INIT_LIST_HEAD(&wb->work_list);
> + INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
> +
> err = fprop_local_init_percpu(&wb->completions, GFP_KERNEL);
> if (err)
> return err;
> @@ -450,7 +450,7 @@ static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
> return 0;
> }
>
> -static void bdi_wb_exit(struct bdi_writeback *wb)
> +static void wb_exit(struct bdi_writeback *wb)
> {
> int i;
>
> @@ -471,11 +471,9 @@ int bdi_init(struct backing_dev_info *bdi)
> bdi->min_ratio = 0;
> bdi->max_ratio = 100;
> bdi->max_prop_frac = FPROP_FRAC_BASE;
> - spin_lock_init(&bdi->wb_lock);
> INIT_LIST_HEAD(&bdi->bdi_list);
> - INIT_LIST_HEAD(&bdi->work_list);
>
> - err = bdi_wb_init(&bdi->wb, bdi);
> + err = wb_init(&bdi->wb, bdi);
> if (err)
> return err;
>
> @@ -510,7 +508,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
> }
>
> bdi_unregister(bdi);
> - bdi_wb_exit(&bdi->wb);
> + wb_exit(&bdi->wb);
> }
> EXPORT_SYMBOL(bdi_destroy);
>
> --
> 1.9.3
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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