Not sure I agree with Red Hat's assessment of swappiness = 0. The point is to aggressively not swap 
. This reminds me why Rich Freeman (errr, Prime) and I had similar ideas behind why we leave it off. For me, this sort of "tuning" doesn't directly command behavior or define a policy. So whether 0, 1, 5, or 30, I'm not really telling the kernel directly to, for example:
. This reminds me why Rich Freeman (errr, Prime) and I had similar ideas behind why we leave it off. For me, this sort of "tuning" doesn't directly command behavior or define a policy. So whether 0, 1, 5, or 30, I'm not really telling the kernel directly to, for example:swap only if I am about to run out of memory (e.g. under 1Mb while under memory pressure)
start swapping memory when system usage is under 50%
start swapping memory when user consumption is over 50%
stop swapping and return everything to main memory if I will have more that 30% free when done
You get the idea.
That said, I feel like I might have hijacked K.S.'s update in regards to swapping on SSD's. Putting aside log-structured file systems which are generally better for SSD use, shouldn't swappiness be turned down on SSD's generally? Doesn't a swappiness of 80 mean you are swapping more than when the system is set to 60?
Also, if that is the case, does that imply you have to run fstrim more?
I'm an XFS user and thankfully realtime discarding is available if I am ok with the performance penalty and I don't want to use batch mode. Something to remember for my next server build which will use an SSD for the system drive.
http://xfs.org/index.php/FITRIM/discard
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Keith C. Perry, MS E.E.
Keith C. Perry, MS E.E.
From: "Gavin W. Burris" <bug@wharton.upenn.edu>
To: "Philadelphia Linux User's Group Discussion List" <plug@lists.phillylinux.org>
Sent: Saturday, July 11, 2015 9:30:14 AM
Subject: Re: [PLUG] swappiness and ssd
To: "Philadelphia Linux User's Group Discussion List" <plug@lists.phillylinux.org>
Sent: Saturday, July 11, 2015 9:30:14 AM
Subject: Re: [PLUG] swappiness and ssd
Is 0 really sane? It was my understanding that swappiness=0 was too
aggressive, almost disables swap all-together. Setting swappiness=1 may
be better, only swapping to avoid the OOM. This, and keeping just a few
gigs of swap as a last-ditch protection, provides a metric to monitor
and avoid.
Big fat warning here, on the Performance Tuning Guide:
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Performance_Tuning_Guide/sect-Red_Hat_Enterprise_Linux-Performance_Tuning_Guide-Memory-Configuration_tools.html#sect-Red_Hat_Enterprise_Linux-Performance_Tuning_Guide-Configuration_tools-Configuring_system_memory_capacity
Cheers.
On Fri 07/10/15 09:24PM -0400, Rich Mingin (PLUG) wrote:
Not at all. It's the default I had recommended to me by the Arch wiki, some
knowledgeable friends, and I think also Rich Prime. It works for me, though
I still have an issue where VMware stalls my whole machine for 5-30 seconds
every 3-5 minutes if I don't manually disable khugepaged defrag. Ah well.
On Fri, Jul 10, 2015 at 9:10 PM, Keith C. Perry <kperry@daotechnologies.com>
wrote:
> Ahh so swappiness=0 is not a weird setting.
>
> ---
> KP-
>
> On Jul 10, 2015 9:05 PM, "Rich Mingin (PLUG)" <plug@frags.us> wrote:
> >
> > I was declining to post, but I'll just chime in, I'm also swappiness=0
> on my machines. The two that touch VMs have 32GB of ram, SSDs, and a small
> swap file on some spinning rust, so I get all of the benefits listed,
> without unneeded SSD wear.
> >
> > On Fri, Jul 10, 2015 at 8:46 PM, Rich Freeman <r-plug@thefreemanclan.net>
> wrote:
> >>
> >> On Fri, Jul 10, 2015 at 6:31 PM, Keith C. Perry
> >> <kperry@daotechnologies.com> wrote:
> >> >
> >> > Rich Freeman, you and I both leave off for similar reasons. Did you
> know
> >> > about this? Looks like a lower setting (like 0 LOL) might get swap
> to
> >> > perform in a "sane" way.
> >> >
> >>
> >> I've never really been satisfied with it, even with a swappiness of 0.
> >>
> >> --
> >> Rich
> >>
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--
Gavin W. Burris
Senior Project Leader for Research Computing
The Wharton School
University of Pennsylvania
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