After disable periodic writeback by writing 0 to dirty_writeback_centisecs, the handler wb_workfn() will not be entered again until the dirty background limit reaches or sync syscall is executed or no enough free memory available or vmscan is triggered. So the periodic writeback can't be enabled by writing a non-zero value to dirty_writeback_centisecs As it can be disabled by sysctl, it should be able to enable by sysctl as well.
Signed-off-by: Yafang Shao <[email protected]> --- mm/page-writeback.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 0b9c5cb..e202f37 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1972,7 +1972,13 @@ bool wb_over_bg_thresh(struct bdi_writeback *wb) int dirty_writeback_centisecs_handler(struct ctl_table *table, int write, void __user *buffer, size_t *length, loff_t *ppos) { - proc_dointvec(table, write, buffer, length, ppos); + unsigned int old_interval = dirty_writeback_interval; + int ret; + + ret = proc_dointvec(table, write, buffer, length, ppos); + if (!ret && !old_interval && dirty_writeback_interval) + wakeup_flusher_threads(0, WB_REASON_PERIODIC); + return 0; } -- 1.8.3.1
