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Commit db125360 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
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writeback: make writeback initiation functions handle multiple bdi_writeback's 



[try_]writeback_inodes_sb[_nr]() and sync_inodes_sb() currently only
handle dirty inodes on the root wb (bdi_writeback) of the target bdi.
This patch implements bdi_split_work_to_wbs() and use it to make these
functions handle multiple wb's.

bdi_split_work_to_wbs() takes a base wb_writeback_work and create
clones of it and issue them to the wb's of the target bdi.  The base
work's nr_pages is distributed using wb_split_bdi_pages() -
ie. according to each wb's write bandwidth's proportion in the bdi.

Cloning a bdi involves memory allocation which may fail.  In such
cases, bdi_split_work_to_wbs() issues the base work directly and waits
for its completion before proceeding to the next wb to guarantee
forward progress and correctness under memory pressure.

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 f30a7d0c

fs/fs-writeback.c

+91 −5
Original line number Diff line number Diff line
@@ -292,6 +292,80 @@ static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages) 
		return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);

}



/**

 * wb_clone_and_queue_work - clone a wb_writeback_work and issue it to a wb

 * @wb: target bdi_writeback

 * @base_work: source wb_writeback_work

 *

 * Try to make a clone of @base_work and issue it to @wb.  If cloning

 * succeeds, %true is returned; otherwise, @base_work is issued directly

 * and %false is returned.  In the latter case, the caller is required to

 * wait for @base_work's completion using wb_wait_for_single_work().

 *

 * A clone is auto-freed on completion.  @base_work never is.

 */

static bool wb_clone_and_queue_work(struct bdi_writeback *wb,

				    struct wb_writeback_work *base_work)

{

	struct wb_writeback_work *work;



	work = kmalloc(sizeof(*work), GFP_ATOMIC);

	if (work) {

		*work = *base_work;

		work->auto_free = 1;

		work->single_wait = 0;

	} else {

		work = base_work;

		work->auto_free = 0;

		work->single_wait = 1;

	}

	work->single_done = 0;

	wb_queue_work(wb, work);

	return work != base_work;

}



/**

 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi

 * @bdi: target backing_dev_info

 * @base_work: wb_writeback_work to issue

 * @skip_if_busy: skip wb's which already have writeback in progress

 *

 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which

 * have dirty inodes.  If @base_work->nr_page isn't %LONG_MAX, it's

 * distributed to the busy wbs according to each wb's proportion in the

 * total active write bandwidth of @bdi.

 */

static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,

				  struct wb_writeback_work *base_work,

				  bool skip_if_busy)

{

	long nr_pages = base_work->nr_pages;

	int next_blkcg_id = 0;

	struct bdi_writeback *wb;

	struct wb_iter iter;



	might_sleep();



	if (!bdi_has_dirty_io(bdi))

		return;

restart:

	rcu_read_lock();

	bdi_for_each_wb(wb, bdi, &iter, next_blkcg_id) {

		if (!wb_has_dirty_io(wb) ||

		    (skip_if_busy && writeback_in_progress(wb)))

			continue;



		base_work->nr_pages = wb_split_bdi_pages(wb, nr_pages);

		if (!wb_clone_and_queue_work(wb, base_work)) {

			next_blkcg_id = wb->blkcg_css->id + 1;

			rcu_read_unlock();

			wb_wait_for_single_work(bdi, base_work);

			goto restart;

		}

	}

	rcu_read_unlock();

}



#else	/* CONFIG_CGROUP_WRITEBACK */



static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
@@ -299,6 +373,21 @@ static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages) 
	return nr_pages;

}



static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,

				  struct wb_writeback_work *base_work,

				  bool skip_if_busy)

{

	might_sleep();



	if (bdi_has_dirty_io(bdi) &&

	    (!skip_if_busy || !writeback_in_progress(&bdi->wb))) {

		base_work->auto_free = 0;

		base_work->single_wait = 0;

		base_work->single_done = 0;

		wb_queue_work(&bdi->wb, base_work);

	}

}



#endif	/* CONFIG_CGROUP_WRITEBACK */



void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
@@ -1599,10 +1688,7 @@ static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr, 
		return;

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



	if (skip_if_busy && writeback_in_progress(&bdi->wb))

		return;



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

	bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);

	wb_wait_for_completion(bdi, &done);

}
@@ -1700,7 +1786,7 @@ void sync_inodes_sb(struct super_block *sb) 
		return;

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



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

	bdi_split_work_to_wbs(bdi, &work, false);

	wb_wait_for_completion(bdi, &done);



	wait_sb_inodes(sb);