writeback: disable periodic old data writeback for !dirty_writeback_centisecs
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>
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@ -852,6 +852,12 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
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unsigned long expired;
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long nr_pages;
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/*
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* When set to zero, disable periodic writeback
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*/
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if (!dirty_writeback_interval)
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return 0;
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expired = wb->last_old_flush +
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msecs_to_jiffies(dirty_writeback_interval * 10);
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if (time_before(jiffies, expired))
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@ -947,8 +953,12 @@ int bdi_writeback_task(struct bdi_writeback *wb)
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break;
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}
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wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
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schedule_timeout_interruptible(wait_jiffies);
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if (dirty_writeback_interval) {
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wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
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schedule_timeout_interruptible(wait_jiffies);
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} else
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schedule();
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try_to_freeze();
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}
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