Date: Sun, 19 May 2019 17:40:30 +0100 From: RW <rwmaillists@googlemail.com> To: freebsd-hackers@freebsd.org Subject: Re: total configured swap exceeds maximum Message-ID: <20190519174030.0206eb41@gumby.homeunix.com> In-Reply-To: <18598E43-CFB1-4C3C-BC46-A4F0DEB569CF@yahoo.com> References: <alpine.BSF.2.20.1905191204540.4805@puchar.net> <20190519160033.0b0e47fa@gumby.homeunix.com> <alpine.BSF.2.20.1905191733230.61441@puchar.net> <18598E43-CFB1-4C3C-BC46-A4F0DEB569CF@yahoo.com>
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On Sun, 19 May 2019 08:53:15 -0700
Mark Millard wrote:
> 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.
In swap_pager.c
/*
* Initialize our zone, guessing on the number we need based
* on the number of pages in the system.
*/
n = vm_cnt.v_page_count / 2;
if (maxswzone && n > maxswzone / sizeof(struct swblk))
n = maxswzone / sizeof(struct swblk);
In i386 maxswzone defaults to a specific value and it is possible to
increase the size. In amd64 maxswzone defaults to 0 which give the
highest value of n permitted.
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