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Commit cc395d7f authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

writeback: implement bdi_wait_for_completion() 



If the completion of a wb_writeback_work can be waited upon by setting
its ->done to a struct completion and waiting on it; however, for
cgroup writeback support, it's necessary to issue multiple work items
to multiple bdi_writebacks and wait for the completion of all.

This patch implements wb_completion which can wait for multiple work
items and replaces the struct completion with it.  It can be defined
using DEFINE_WB_COMPLETION_ONSTACK(), used for multiple work items and
waited for by wb_wait_for_completion().

Nobody currently issues multiple work items and this patch doesn't
introduce any behavior changes.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent ac7b19a3

fs/fs-writeback.c

+46 −12
Original line number Diff line number Diff line
@@ -34,6 +34,10 @@ 
 */

#define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_CACHE_SHIFT - 10))



struct wb_completion {

	atomic_t		cnt;

};



/*

 * Passed into wb_writeback(), essentially a subset of writeback_control

 */
@@ -51,9 +55,22 @@ struct wb_writeback_work { 
	enum wb_reason reason;		/* why was writeback initiated? */



	struct list_head list;		/* pending work list */

	struct completion *done;	/* set if the caller waits */

	struct wb_completion *done;	/* set if the caller waits */

};



/*

 * If one wants to wait for one or more wb_writeback_works, each work's

 * ->done should be set to a wb_completion defined using the following

 * macro.  Once all work items are issued with wb_queue_work(), the caller

 * can wait for the completion of all using wb_wait_for_completion().  Work

 * items which are waited upon aren't freed automatically on completion.

 */

#define DEFINE_WB_COMPLETION_ONSTACK(cmpl)				\

	struct wb_completion cmpl = {					\

		.cnt		= ATOMIC_INIT(1),			\

	}





/*

 * If an inode is constantly having its pages dirtied, but then the

 * updates stop dirtytime_expire_interval seconds in the past, it's
@@ -161,17 +178,34 @@ static void wb_queue_work(struct bdi_writeback *wb, 
	trace_writeback_queue(wb->bdi, work);



	spin_lock_bh(&wb->work_lock);

	if (!test_bit(WB_registered, &wb->state)) {

		if (work->done)

			complete(work->done);

	if (!test_bit(WB_registered, &wb->state))

		goto out_unlock;

	}

	if (work->done)

		atomic_inc(&work->done->cnt);

	list_add_tail(&work->list, &wb->work_list);

	mod_delayed_work(bdi_wq, &wb->dwork, 0);

out_unlock:

	spin_unlock_bh(&wb->work_lock);

}



/**

 * wb_wait_for_completion - wait for completion of bdi_writeback_works

 * @bdi: bdi work items were issued to

 * @done: target wb_completion

 *

 * Wait for one or more work items issued to @bdi with their ->done field

 * set to @done, which should have been defined with

 * DEFINE_WB_COMPLETION_ONSTACK().  This function returns after all such

 * work items are completed.  Work items which are waited upon aren't freed

 * automatically on completion.

 */

static void wb_wait_for_completion(struct backing_dev_info *bdi,

				   struct wb_completion *done)

{

	atomic_dec(&done->cnt);		/* put down the initial count */

	wait_event(bdi->wb_waitq, !atomic_read(&done->cnt));

}



#ifdef CONFIG_CGROUP_WRITEBACK



/**
@@ -1143,7 +1177,7 @@ static long wb_do_writeback(struct bdi_writeback *wb) 


	set_bit(WB_writeback_running, &wb->state);

	while ((work = get_next_work_item(wb)) != NULL) {

		struct completion *done = work->done;

		struct wb_completion *done = work->done;



		trace_writeback_exec(wb->bdi, work);
@@ -1151,8 +1185,8 @@ static long wb_do_writeback(struct bdi_writeback *wb) 


		if (work->auto_free)

			kfree(work);

		if (done)

			complete(done);

		if (done && atomic_dec_and_test(&done->cnt))

			wake_up_all(&wb->bdi->wb_waitq);

	}



	/*
@@ -1518,7 +1552,7 @@ void writeback_inodes_sb_nr(struct super_block *sb, 
			    unsigned long nr,

			    enum wb_reason reason)

{

	DECLARE_COMPLETION_ONSTACK(done);

	DEFINE_WB_COMPLETION_ONSTACK(done);

	struct wb_writeback_work work = {

		.sb			= sb,

		.sync_mode		= WB_SYNC_NONE,
@@ -1533,7 +1567,7 @@ void writeback_inodes_sb_nr(struct super_block *sb, 
		return;

	WARN_ON(!rwsem_is_locked(&sb->s_umount));

	wb_queue_work(&bdi->wb, &work);

	wait_for_completion(&done);

	wb_wait_for_completion(bdi, &done);

}

EXPORT_SYMBOL(writeback_inodes_sb_nr);
@@ -1600,7 +1634,7 @@ EXPORT_SYMBOL(try_to_writeback_inodes_sb); 
 */

void sync_inodes_sb(struct super_block *sb)

{

	DECLARE_COMPLETION_ONSTACK(done);

	DEFINE_WB_COMPLETION_ONSTACK(done);

	struct wb_writeback_work work = {

		.sb		= sb,

		.sync_mode	= WB_SYNC_ALL,
@@ -1618,7 +1652,7 @@ void sync_inodes_sb(struct super_block *sb) 
	WARN_ON(!rwsem_is_locked(&sb->s_umount));



	wb_queue_work(&bdi->wb, &work);

	wait_for_completion(&done);

	wb_wait_for_completion(bdi, &done);



	wait_sb_inodes(sb);

}

include/linux/backing-dev-defs.h

+2 −0
Original line number Diff line number Diff line
@@ -155,6 +155,8 @@ struct backing_dev_info { 
	struct rb_root cgwb_congested_tree; /* their congested states */

	atomic_t usage_cnt; /* counts both cgwbs and cgwb_contested's */

#endif

	wait_queue_head_t wb_waitq;



	struct device *dev;



	struct timer_list laptop_mode_wb_timer;

mm/backing-dev.c

+1 −0
Original line number Diff line number Diff line
@@ -768,6 +768,7 @@ int bdi_init(struct backing_dev_info *bdi) 
	bdi->max_ratio = 100;

	bdi->max_prop_frac = FPROP_FRAC_BASE;

	INIT_LIST_HEAD(&bdi->bdi_list);

	init_waitqueue_head(&bdi->wb_waitq);



	err = wb_init(&bdi->wb, bdi, GFP_KERNEL);

	if (err)