Function bwillwrite

freebsd/kern/vfs_bio.c:2577–2590

* bwillwrite: * * Called prior to the locking of any vnodes when we are expecting to * write. We do not want to starve the buffer cache with too many * dirty buffers so we block here. By blocking prior to the locking * of any vnodes we attempt to avoid the situation where a locked vnode * prevents the various system daemons from flushing related buffers. */

 *	prevents the various system daemons from flushing related buffers.
 */
void
bwillwrite(void)
{

	if (buf_dirty_count_severe()) {
		mtx_lock(&bdirtylock);
		while (buf_dirty_count_severe()) {
			bdirtywait = 1;
			msleep(&bdirtywait, &bdirtylock, (PRIBIO + 4),
			    "flswai", 0);
		}
		mtx_unlock(&bdirtylock);
	}
}

/*
 * Return true if we have too many dirty buffers.