// SPDX-License-Identifier: GPL-2.0-only
/*
 * Complete scope from Linux v6.18 fs/fs-writeback.c.
 * Source: https://github.com/torvalds/linux/blob/v6.18/fs/fs-writeback.c
 * Kernel excerpt; not a standalone program.
 * The book exact source tag is not asserted.
 */

/*
 * fs/fs-writeback.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 *
 * Contains all the functions related to writing back and waiting
 * upon dirty inodes against superblocks, and writing back dirty
 * pages against inodes.  ie: data writeback.  Writeout of the
 * inode itself is not handled here.
 *
 * 10Apr2002	Andrew Morton
 *		Split out of fs/inode.c
 *		Additions for address_space-based writeback
 */

static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
{
	if (!wb_has_dirty_io(wb))
		return;

	/*
	 * All callers of this function want to start writeback of all
	 * dirty pages. Places like vmscan can call this at a very
	 * high frequency, causing pointless allocations of tons of
	 * work items and keeping the flusher threads busy retrieving
	 * that work. Ensure that we only allow one of them pending and
	 * inflight at the time.
	 */
	if (test_bit(WB_start_all, &wb->state) ||
	    test_and_set_bit(WB_start_all, &wb->state))
		return;

	wb->start_all_reason = reason;
	wb_wakeup(wb);
}