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From: Grant <emailgrant@gmail.com>
Date: Sun, 9 Oct 2016 06:25:20 -0700
Message-ID: <CAN0CFw18hs3UWiNtrmWQQ3vHtccGKjaa=CsTnskMf6+omm9f5Q@mail.gmail.com>
Subject: Re: [gentoo-user] Re: Strive for zero swap usage?
To: Gentoo mailing list <gentoo-user@lists.gentoo.org>
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> Looking at the times, it looks a lot like you are having higher iowait
> only at around 2:00 and 4:20 which are pretty standard cron job times.
> These probably run niced or ioniced. It's normal that you are seeing
> higher iowait for such processes.
>
> You may want to try setting your io scheduler to deadline (or even noop
> if you are using a RAID controller with bbu and write cache). Since you
> seem to prefer response times over throughput you should be using
> deadline io scheduler anyways. Actually, don't use the default CFQ if
> your server is virtualized. At least in my tests, CFQ seems to work a
> lot against what virtualized IO seems to achieve.
I'm using CFQ now, no virtualization. I should use CFQ if I prefer
throughput and deadline for response time?
> I also suggest using maybe XFS as a filesystem. Which one are you using?
I'm using ext3 but I plan to move to ZFS.
> If your server is a web server and it starts swapping, there is not
> much you can do against it. Tuning swappiness will probably not help at
> all. Get more RAM or lower your memory usage. If, for example, MySQL
> runs on the same host, either move it or lower it's memory usage.
> Reduce the amount of apache application processes running at the same
> time (PHP, Perl, whatever), use a layered application stack: One
> frontend for handling static files, one middleware server for handling
> requests over to PHP and doing the request dispatch queue, and reduce
> memory/IO footprint of your backend.
Changing swappiness from 60 to 30 has drastically reduced swap usage
but I'm not sure how much it has done for iowait and response times.
I'll know more in a few days. If swap usage stays very low and I'm
still not happy with the consistency of response times, I would think
reducing memory usage won't help.
- Grant