On Fri, 2013-01-11 at 12:25 +0100, Zlatko Calusic wrote: > On 11.01.2013 02:25, Simon Jeons wrote: > > On Wed, 2013-01-09 at 22:41 +0100, Zlatko Calusic wrote: > >> From: Zlatko Calusic <zlatko.calusic@xxxxxxxx> > >> > >> Currently we take a short nap (HZ/10) and wait for congestion to clear > >> before taking another pass with lower priority in balance_pgdat(). But > >> we do that only for the highest zone that we encounter is unbalanced > >> and congested. > >> > >> This patch changes that to wait on all congested zones in a single > >> pass in the hope that it will save us some scanning that way. Also we > >> take a nap as soon as congested zone is encountered and sc.priority < > >> DEF_PRIORITY - 2 (aka kswapd in trouble). > > > > But you still didn't explain what's the problem you meat and what > > scenario can get benefit from your change. > > > > I did in my reply to Andrew. Here's the relevant part: > > > I have an observation that without it, under some circumstances that > > are VERY HARD to repeat (many days need to pass and some stars to align > > to see the effect), the page cache gets hit hard, 2/3 of it evicted in > > a split second. And it's not even under high load! So, I'm still > > monitoring it, but so far the memory utilization really seems better > > with the patch applied (no more mysterious page cache shootdowns). > > The scenario that should get benefit is everyday. I observed problems during > light but constant reading from disk (< 10MB/s). And sending that data > over the network at the same time. Think backup that compresses data on the > fly before pushing it over the network (so it's not very fast). > > The trouble is that you can't just fix up a quick benchmark and measure the > impact, because many days need to pass for the bug to show up in all it's beauty. > > Is there anybody out there who'd like to comment on the patch logic? I.e. do > you think that waiting on every congested zone is the more correct solution > than waiting on only one (only the highest one, and ignoring the fact that > there may be other even more congested zones)? What's the benefit of waiting on every congested zone than waiting on only one against your scenario? > > Regards, -- Simon Jeons <simon.jeons@xxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>