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Date:      Sun, 19 May 2019 08:53:15 -0700
From:      Mark Millard <marklmi@yahoo.com>
To:        Wojciech Puchar <wojtek@puchar.net>
Cc:        RW <rwmaillists@googlemail.com>, freebsd-hackers@freebsd.org
Subject:   Re: total configured swap  exceeds maximum 
Message-ID:  <18598E43-CFB1-4C3C-BC46-A4F0DEB569CF@yahoo.com>
In-Reply-To: <alpine.BSF.2.20.1905191733230.61441@puchar.net>
References:  <alpine.BSF.2.20.1905191204540.4805@puchar.net> <20190519160033.0b0e47fa@gumby.homeunix.com> <alpine.BSF.2.20.1905191733230.61441@puchar.net>
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On 2019-May-19, at 08:33, Wojciech Puchar <wojtek@puchar.net> wrote:

>>> what should i set kern.maxswzone to ? it is 0
>>> 
>>> # sysctl  kern.maxswzone
>>> kern.maxswzone: 0
>> 
>> IIRC for amd64 kern.maxswzone=0 represents the maximum allowed.
> so i cannot have more VM than 5*RAM?

There is is a kernel memory tradeoff structure to increase in
kern.maxswzone being larger as I understand. Quoting "man 8 loader"
(but the "eight times" is system/architecture specific and will
likely be different):

   kern.maxswzone
                 Limits the amount of KVM to be used to hold swap metadata,
                 which directly governs the maximum amount of swap the
                 system can support, at the rate of approximately 200 MB of
                 swap space per 1 MB of metadata.  This value is specified
                 in bytes of KVA space.  If no value is provided, the system
                 allocates enough memory to handle an amount of swap that
                 corresponds to eight times the amount of physical memory
                 present in the system.

                 Note that swap metadata can be fragmented, which means that
                 the system can run out of space before it reaches the
                 theoretical limit.  Therefore, care should be taken to not
                 configure more swap than approximately half of the
                 theoretical maximum.

                 Running out of space for swap metadata can leave the system
                 in an unrecoverable state.  Therefore, you should only
                 change this parameter if you need to greatly extend the KVM
                 reservation for other resources such as the buffer cache or
                 kern.ipc.nmbclusters.  Modifies kernel option
                 VM_SWZONE_SIZE_MAX.

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)

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