Memory usage appears a bit high

[James B. Byrne]

On Wed, January 16, 2019 13:11, Steve O'Hara-Smith wrote:
> On Wed, 16 Jan 2019 12:46:39 -0500
> "James B. Byrne" <byrnejb at harte-lyne.ca> wrote:
>
>>
>>
>> On Wed, January 16, 2019 12:36, Steve O'Hara-Smith wrote:
>> > On Wed, 16 Jan 2019 12:31:14 -0500
>> > "James B. Byrne via freebsd-questions"
>> <freebsd-questions at freebsd.org>
>> > wrote:
>> >
>> >> We have an Cyrus IMAP service running on a BHyve FreeBSD-11.2p7
>> vm.
>> >> It has 4 Gb allocated.  I have noticed that top reports this:
>> >>
>> >> Mem: 164M Active, 204M Inact, 22M Laundry, 3426M Wired, 111M Free
>> >
>> > 	Are you running ZFS ? If so then most of the wired memory is
>> > probably ARC.
>> >
>>
>> Yes, we are running the vm using zfs.
>>
>> ARC: 2432M Total, 451M MFU, 1683M MRU, 8480K Anon, 38M Header,
>>      252M Other
>>      1828M Compressed, 3768M Uncompressed, 2.06:1 Ratio
>
> The ARC - ZFS cache is always in wired memory because it's kernel
> space buffers and it does have a tendency to eat all the memory
> it can get unless you constrain it by setting vfs.zfs.arc_max sysctl.
>

As I have never meddled with the sysctl settings on this bhyve host I
infer that this setting in sysctl is calculated based on the total
memory allocated when the vm is created:

vfs.zfs.arc_max: 3043799040

How much should be committed to arc in a 4GB system?  What are the
benefits / costs of more or less ram allocated to arc?

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James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
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