[gentoo-amd64] Re: System becomes almost unusable when compling c++ code

[Duncan <1i5t5.duncan@cox.net>]

Richard Freeman <rich@thefreemanclan.net> posted
46B33881.2060801@thefreemanclan.net, excerpted below, on  Fri, 03 Aug 2007
10:15:29 -0400:

> Actually, as long as you have enough swap your RAM doesn't really
> matter.  In the worst case it just swaps to disk, which is what it would
> be doing anyway if you didn't have a tmpfs.  Even if only 10% of the
> short-lived files didn't make it to disk it would be a huge savings in
> IO waits.

Thanks for pointing that out, yes.

> Also, consider using ionice (from schedutils I think) - it lets you
> schedule IO the way nice schedules CPU.  It can have a big impact if you
> have a lot of disk churn.

It can.  However, with the proper i/o scheduler (CFQ), plain nice is 
often good enough, since the i/o scheduler implements logical defaults 
based on nice value -- higher nice means higher default ionice.

That did get me to switch i/o schedulers here, BTW.  I had been using 
anticipatory until I setup the RAID, at which point I switched to the 
simpler deadline, since anticipatory does its anticipation stuff assuming 
a single spindle.  After reading a bit about the workings of ionice 
however, and how CFQ defaults i/o priority based on CPU timeslice 
priority (and therefore nice), I switched to it.  With the memory I have, 
most disk access after the initial is cached, so it didn't affect me a 
lot, and RAID helps in that regard as well, but it did seem to make some 
difference.

So anyway, I'm in pretty strong agreement with you. =8^)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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