Re: ZFS deadlocks/memory accounting issues

<<On Mon, 16 Mar 2026 15:55:59 -0600, Alan Somers <asomers@freebsd.org> said:

> On Mon, Mar 16, 2026 at 3:39 PM Garrett Wollman <wollman@bimajority.org> wrote:

>> None of our systems are set up for that.  They all have huge memory
>> and pretty tiny swap partitions, and in any case, they don't panic,
>> they just deadlock.  Or the OOM killer just shoots all user processes;
>> these are nearly indistinguishable from a service provider's
>> perspective.

> Pretty tiny swap partitions?

Tiny compared to RAM, typically 16 or 32 GiB.  After all, these are
NFS servers, they shouldn't have more than a few dozen MiB of
swappable anonymous memory.(*)  We're not going to put a 2T SSD as a
hopefully-never-to-be-used swap drive in a file server.

I configured a dump device on the server that crashed today, if it
crashes again when I'm at a keyboard I'll see if I can get to write a
dump in the 32 GiB of swap that it has configured.

-GAWollman

(*) If the kernel erroneously thinks it's out of free memory and
swapping stuff out only opens up a few MiB, that would certainly
explain why it goes on to ARC eviction and eventual OOM.  On this
server, after two hours of uptime, I see:

Device          1K-blocks     Used    Avail Capacity
/dev/gpt/swap0   33554432    32132 33522300     0%