Messages in this thread | | | Date | Mon, 17 Jun 2002 14:21:33 -0700 | From | Andrew Morton <> | Subject | Re: [patch 1/19] writeback tunables |
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Russell King wrote: > > On Mon, Jun 17, 2002 at 12:33:18PM +0200, Martin Dalecki wrote: > ... > > > +int dirty_expire_centisecs = 30 * 100; > > > + > > > > Blind guess - didn't the 100 wan't to be HZ?! > > The units are centiseconds (as the name suggests). 5 * 100 centiseconds = 5 > seconds, so the dirty writeback timeout is 5 seconds. Check the code a > little further and you'll see HZ gets factored into them on use. >
Yup. Sorry about the "_centisecs" thing. That's a bit anal, but I tend to think that it's best to be really explicit about the units, make it a bit easier to use. I don't know how many times I've had to peer in fs/buffer.c to remember what those dang numbers do.
Possibly, "seconds" may be sufficiently high resolution for these things. But I wasn't sure - maybe someone wants to run the kupdate function five times per second? Dunno.
There are some departures from 2.4 tradition which are worth mentioning here:
- There is no range checking on the settings. (But a divide-by zero isn't possible, so I think that's OK)
- Unlike the 2.4 bdflush settings, these parameters are not updated in a single hit. So if you modify them by a large amount while the system is under heavy writeback load, perhaps some whacky things will happen if you create an irrational intermediate state. But that's quite unlikely.
- Unlike 2.4, the settings are scaled by HZ. So that bdflush tuning tool whose name I forget will no longer make kupdate run ten times too fast on Alphas.
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