On Thu, Apr 14, 2011 at 07:31:22AM +0800, Wu Fengguang wrote: > On Thu, Apr 14, 2011 at 06:04:44AM +0800, Jan Kara wrote: > > On Wed 13-04-11 16:59:41, Wu Fengguang wrote: > > > Reduce the dampening for the control system, yielding faster > > > convergence. The change is a bit conservative, as smaller values may > > > lead to noticeable bdi threshold fluctuates in low memory JBOD setup. > > > > > > CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > > > CC: Richard Kennedy <richard@xxxxxxxxxxxxxxx> > > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > Well, I have nothing against this change as such but what I don't like is > > that it just changes magical +2 for similarly magical +0. It's clear that > > The patch tends to make the rampup time a bit more reasonable for > common desktops. From 100s to 25s (see below). > > > this will lead to more rapid updates of proportions of bdi's share of > > writeback and thread's share of dirtying but why +0? Why not +1 or -1? So > > Yes, it will especially be a problem on _small memory_ JBOD setups. > Richard actually has requested for a much radical change (decrease by > 6) but that looks too much. > > My team has a 12-disk JBOD with only 6G memory. The memory is pretty > small as a server, but it's a real setup and serves well as the > reference minimal setup that Linux should be able to run well on. FWIW, linux runs on a lot of low power NAS boxes with jbod and/or raid setups that have <= 1GB of RAM (many of them run XFS), so even your setup could be considered large by a significant fraction of the storage world. Hence you need to be careful of optimising for what you think is a "normal" server, because there simply isn't such a thing.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
