On Fri, Oct 08, 2010 at 09:57:04PM +0800, Wu Fengguang wrote: > On Fri, Oct 08, 2010 at 06:27:09PM +0800, Yong Wang wrote: > > On Fri, Oct 08, 2010 at 01:28:07PM +0300, Artem Bityutskiy wrote: > > > On Fri, 2010-10-08 at 18:27 +0800, Wu, Xia wrote: > > > > > However, when the next wake-up interrupt happens is not defined. It can > > > > > happen 1ms after, or 1 minute after, or 1 hour after. What Christoph > > > > > says is that there should be some guarantee that sb writeout starts, > > > > > say, within 5 to 10 seconds interval. Deferrable timers do not guarantee > > > > > this. But take a look at the range hrtimers - they do exactly this. > > > > > > > > If the system is in sleep state, is there any data which should be written? > > > > > > May be yes, may be no. > > > > > > > Thanks for the quick response, Artem. May I know what might need to be > > written out when system is really idle? > > system idle != no dirty inodes Ah sorry -- I missed the context. Please ignore the following paragraphs for sync_supers.. Thanks, Fengguang > Imagine an application dirties 100MB data and quits. The system then > goes quiet for very long time. In this case we still want the flusher > thread to wake up within 30 seconds to flush the 100MB dirty data. > It's a contract that dirty data will be synced to disk after 30s > (which is the default value of /proc/sys/vm/dirty_expire_centisecs). > > Note that 30s is not an exact value. A dirty page may be synced to > disk when it's been dirtied for 35s. The 5s error comes from the > flusher wakeup interval (/proc/sys/vm/dirty_writeback_centisecs). > > Thanks, > Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>