Re: [PLUG] swappiness and ssd

[Josh Zenker <jzenker@gmail.com>]

On Jul 13, 2015 11:47 AM, "Keith C. Perry" <kperry@daotechnologies.com> wrote:
>
> Rich, sounds like K.S. is getting some decent performance...
>
> K.S., I generally run XFS too but have you tried running any other filesystems on your SSD?  Swap usage is one thing but the journaling is going to increase the numbers of writes too and I would be worried about that.  'Not sure how to quantify this or if it really matters in a practical sense.

As long as you're mounting with noatime or relatime and not making frequent changes, I would not expect journaling to add many writes. And I believe relatime is the default in newer versions of the kernel.

>
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
> Keith C. Perry, MS E.E.
> Owner, DAO Technologies LLC
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>
> ----- Original Message -----
> From: "Rich Freeman" <r-plug@thefreemanclan.net>
> To: "Philadelphia Linux User's Group Discussion List" <plug@lists.phillylinux.org>
> Sent: Sunday, July 12, 2015 3:49:49 PM
> Subject: Re: [PLUG] swappiness and ssd
>
> On Sun, Jul 12, 2015 at 10:14 AM, K.S. Bhaskar <bhaskar@bhaskars.com> wrote:
> >
> > The traditional view of swapping is that it is undesirable because reading
> > from swap is slow, and swap should therefore be used only if unavoidable.
> > Therefore, the received wisdom is to set a low value of swappiness, to swap
> > only when unavoidable, and take a performance hit when that happened.
> >
> > But, write cycle limits aside, I believe SSDs require a rethink.
>
> I'd be very interested in feedback from those using swap on SSD.
> However, I never thought that swapiness=0 was conventional wisdom on
> Linux.  I can think of a million reasons why a higher setting /should/
> be better.  The problem is that it often isn't, and that is just due
> to limitations in Linux and how it is used.  The defaults probably
> make running updatedb twice in a row a lot faster, but the problem is
> that nobody actually does that, and all that swapping after running it
> once kills everything else you do.
>
> It has been a while since I've run with swap, so it is possible that
> things have gotten better.  I do agree that performance of swap should
> be much better on an SSD.
>
> The other thing I'd be concerned with is ssd write cycles.  I've tried
> to move a lot of my heavy-modification activities off of ssd for this
> reason.  Swap is going to tend to wear it faster.
>
> --
> Rich
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