Setting sysctl vfs.zfs.arc_max failed: 22

[Steven Hartland]

Thanks for testing Nathan, that is the expected behaviour it might be 
nice if we had the concept of a sysctl which is at its auto value and 
hence we could use that to determine if we should recalculate said 
automatic values which hadn't been manually set but we don't have that 
unfortunately.

On 08/07/2016 07:48, Nathan Bosley wrote:
> I was just testing this a bit.
> I can now set max in loader.conf as expected.
>
> I did notice one thing that I thought was a bit strange though.
>
> As a reference, here are my defaults without any ARC tunables/sysctls:
>
> vfs.zfs.arc_meta_limit: 3903459328
> vfs.zfs.arc_min: 1951729664
> vfs.zfs.arc_max: 15613837312
>
> If I put vfs.zfs.arc_max="8589934592" in loader.conf, the results are:
>
> vfs.zfs.arc_meta_limit: 2147483648
> vfs.zfs.arc_min: 1073741824
> vfs.zfs.arc_max: 8589934592
>
> So meta_limit and min are also changed, which is reasonable.
>
> If I remove all of my ARC tunables in loader.conf, so that I have the 
> default values after booting, and then use:
> # sysctl vfs.zfs.arc_max="8589934592"
>
> The result is:
>
> vfs.zfs.arc_meta_limit: 2147483648
> vfs.zfs.arc_min: 1951729664
> vfs.zfs.arc_max: 8589934592
>
> Max was set as requested.
> meta_limit was set to max/4.
> But min is still at the default.
>
> In other words, if I use loader.conf to set max, then min and 
> meta_limit are also recalculated.
> But if I use sysctl to set max, only meta_limit is recalculated; min 
> remains at the default.
> I'm not sure if that's the intent.
>
> Just a heads-up.
>
> Thanks again.
>
> On Wed, Jul 6, 2016 at 7:51 PM, Steven Hartland 
> <killing at multiplay.co.uk <mailto:killing at multiplay.co.uk>> wrote:
>
>     On 06/07/2016 21:39, Eric van Gyzen wrote:
>
>         On 07/06/16 03:35 PM, Steven Hartland wrote:
>
>             The ARC settings and kmem aren't initialised when tunables
>             are loaded
>             so the tests fail.
>
>             I've fixed this locally by blindly setting if ARC is not
>             configured.
>             Request to commit the fix is with re@
>
>             In the mean time the patch is attached.
>
>             Thanks for the report and sorry about the breakage.
>
>         No worries.  Thanks for the quick fix.
>
>     https://svnweb.freebsd.org/changeset/base/302382
>
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