writeback: disable periodic old data writeback for !dirty_writeback_centisecs (69b62d01) · Commits · 戴 / test

Prior to 2.6.32, setting /proc/sys/vm/dirty_writeback_centisecs disabled periodic dirty writeback from kupdate. This got broken and now causes excessive sys CPU usage if set to zero, as we'll keep beating on schedule(). Cc: stable@kernel.org Reported-by:

Justin Maggard <jmaggard10@gmail.com> Signed-off-by:

Jens Axboe <jens.axboe@oracle.com>

fs/fs-writeback.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -852,6 +852,12 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
		unsigned long expired;
		long nr_pages;

		/*
		* When set to zero, disable periodic writeback
		*/
		if (!dirty_writeback_interval)
		return 0;

		expired = wb->last_old_flush +
		msecs_to_jiffies(dirty_writeback_interval * 10);
		if (time_before(jiffies, expired))
		@@ -947,8 +953,12 @@ int bdi_writeback_task(struct bdi_writeback *wb)
		break;
		}

		if (dirty_writeback_interval) {
		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
		schedule_timeout_interruptible(wait_jiffies);
		} else
		schedule();

		try_to_freeze();
		}

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