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Date:      Mon, 28 Dec 2020 04:53:58 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 252227] Default value of vm.max_wired is too low in 12.2
Message-ID:  <bug-252227-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D252227

            Bug ID: 252227
           Summary: Default value of vm.max_wired is too low in 12.2
           Product: Base System
           Version: 12.2-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: vvd@unislabs.com

On 12.2 look like vm.max_wired is a hard limit for number of wired pages for
user processes.
With 48GB of RAM default value is 9727317 - it's 9727317*4096/1024/1024/102=
4 =3D
~37.1GB only.
Use case:
1) I see 9GB of free RAM
2) started VM in VirtualBox with 8GB
3) started applications in VM
4) VM freezes with VERR_NO_MEMORY error in VBox.log
5) stopped VM
6) 46*1024*1024*1024/4096 =3D 12058624
sysctl vm.max_wired=3D12058624
7) repeat 2) and 3)
8) VM work fine now

/usr/src/sys/vm/vm_pageout.c (2082):
vm_page_max_user_wired =3D 4 * freecount / 5;

>From dmesg: avail memory =3D 50130972672 (47808 MB)
47808 MB * 4/5/1024 =3D 37.35GB ~=3D 37.1GB

IMHO, it's very incorrect!
Something like 99/100 look more correct for VM servers with total RAM 48GB:
47808*99/100/1024 =3D 46.220625

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