Date: Sat, 4 Jan 2025 19:47:16 +0100 From: Miroslav Lachman <000.fbsd@quip.cz> To: Karl Denninger <karl@denninger.net>, freebsd-hackers@freebsd.org Subject: Re: curious crashes when under memory pressure Message-ID: <7276b34f-bba9-41a7-afd9-8505c83f8e08@quip.cz> In-Reply-To: <33db3282-25c4-42fb-8d97-1918d52fa9e2@denninger.net> References: <CAPx1GvfwqFqvMm0RkTvxa4BJStvOdG0=pNx2dCuWEzCXsqhqHw@mail.gmail.com> <slrnvnij2h.26bu.pmc@disp.intra.daemon.contact> <CAPx1GvfOh4g1AeOcYXC26W5jbPAgA_E_t7CW9chg4miC8c15-w@mail.gmail.com> <9e71d8eb-74c3-4bcb-89b1-90d4f9746168@quip.cz> <33db3282-25c4-42fb-8d97-1918d52fa9e2@denninger.net>
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On 04/01/2025 18:36, Karl Denninger wrote: > > On 1/4/2025 12:30, Miroslav Lachman wrote: >> On 04/01/2025 17:27, Chris Torek wrote: >>> On Sat, Jan 4, 2025 at 7:01 AM Peter 'PMc' Much [..] >> Do you have swap on ZFS or not (in the first post you said "swapping >> to a zfs mirror")? If yes then it can cause the problems in memory >> pressure because system has no free memory but ZFS needs memory. >> If you want the swap on a mirror, then use separate partition on 2 >> disks and add gmirror on top of them. >> >> Kind regards >> Miroslav Lachman >> > What's the argument for swapping to a mirror in the first place? If the > issue is throughput IMHO the answer is to swap to multiple devices. Redundancy in case of disk failure. I've seen many disk failures over the years, and when you have a swap concatenated from partitions on 2 disks, the whole system mirrored on 2 disks, and 1 disk fails, the system crashes. That's why we've always used swap over gmirrored partitions. Then we can pull out one disk when system is running and replace it with a new disk. > Putting swap through a filesystem abstraction as noted above runs the > risk of requiring an allocation of RAM for the operation to complete > when you're desperately short on it in the first place resulting in > serious trouble. Kind regards Miroslav Lachman
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