Date: Wed, 16 Jan 2019 15:45:08 -0500 From: "James B. Byrne" <byrnejb@harte-lyne.ca> To: "Steve O'Hara-Smith" <steve@sohara.org> Cc: byrnejb@harte-lyne.ca, freebsd-questions@freebsd.org Subject: Re: Memory usage appears a bit high Message-ID: <8f1f1f6c5532a9b076d878ff98a9044c.squirrel@webmail.harte-lyne.ca> In-Reply-To: <20190116181146.375e2358d2091380c74a8291@sohara.org> References: <35c451bc1733004b7d868f60da68c639.squirrel@webmail.harte-lyne.ca> <20190116173621.9d90157c1adf526298763415@sohara.org> <0c45ab67b1480d39dd87059495f6a27c.squirrel@webmail.harte-lyne.ca> <20190116181146.375e2358d2091380c74a8291@sohara.org>
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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@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@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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