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Hermes SMTP Server) with ESMTPA ID 9fd0a045fe28989fd439c03eed71057a; Tue, 11 Nov 2025 18:24:58 +0000 (UTC) Content-Type: text/plain; charset=utf-8 List-Id: Discussions about the use of FreeBSD-current List-Archive: https://lists.freebsd.org/archives/freebsd-current List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-current@FreeBSD.org Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.700.81\)) Subject: Re: kernel: warning: total configured swap (493567 pages) exceeds maximum recommended amount From: Mark Millard In-Reply-To: <86ms4sv73u.fsf@ltc.des.dev> Date: Tue, 11 Nov 2025 10:24:47 -0800 Cc: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= , freebsd-current@freebsd.org, freebsd-arm@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: <3C656BFD-BDBD-4E83-AD62-9FBDE14A94D2@yahoo.com> References: <86qzu4vazw.fsf@ltc.des.dev> <86ms4sv73u.fsf@ltc.des.dev> To: bob prohaska X-Mailer: Apple Mail (2.3826.700.81) X-Spamd-Bar: ---- X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[] X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Rspamd-Queue-Id: 4d5ZhM0hZ2z3ymm On Nov 11, 2025, at 08:58, Dag-Erling Sm=C3=B8rgrav = wrote: > bob prohaska writes: >> So I'm flirting with trouble on a system (Pi2/armv7 FWIW) reporting >> warning: total configured swap (1024000 pages) exceeds maximum = recommended amount (467488 pages). >> warning: increase kern.maxswzone or reduce amount of swap. ? >=20 > The maximum recommended amount is half the maximum supported amount, = so > you not only have more swap than recommended, you have more swap than > the kernel can actually use (467488 * 2 =3D 934976 pages) and should > consider either increasing kern.maxswzone so the kernel can use all of > the swap you've configured (at the cost of slightly reducing usasble > physical memory) or decreasing the amount of swap. Beyond the issue of having more swap than can even be used under the best-case kind of contexts, given other defaults in use, there is the following documented property. (In order to put a copy of the below note with this other related material.) QUOTE man 8 loader_simp reports: kern.maxswzone . . . 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. . . . END QUOTE This means that using more than the 467488 pages of swap, given the default kern.maxswzone (or vm.swzone), runs the greater risk of having fragmentation in the data structure lead to running out of space before the swap space is fully used. But another paragraph for kern.maxswzone in that man page reports: "Running out of space for swap metadata can leave the system in an unrecoverable state. . . ." However, if I remember right, you have reported testing with the swap adjusted to not produce the warning --and still got the status of losing control and getting no more output to look at. If so, the above is not directly a solution to the specific problem. (It still may be a good idea to not be oddly configured while trying to find a solution to your active problem.) That paragraph continues by mentioning other tradeoffs related to kern.maxswzone adjustments: ". . . 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." [I wonder if the "only change" wording should explicitly indicate a specific direction (increase vs. decrease) instead.] Side note: I'll note that FreeBSD updates can change the detailed 467488 figure that is computed some. Using the exact figure can lead to future warning messages. Leaving some margin for variation can cut down on this. =3D=3D=3D Mark Millard marklmi at yahoo.com