Preserving guest memory across kexec [LWN.net]

Preserving guest memory across kexec

Posted May 20, 2022 16:34 UTC (Fri) by developer122 (guest, #152928)
In reply to: Preserving guest memory across kexec by developer122
Parent article: Preserving guest memory across kexec

I wonder, if at some point in the future we will be asking how the linux kernel might preserve a select few processes across reboots?

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Preserving guest memory across kexec

Posted May 20, 2022 16:47 UTC (Fri) by mb (subscriber, #50428) [Link] (4 responses)

Checkpoint + restore?
https://en.wikipedia.org/wiki/CRIU

Preserving guest memory across kexec

Posted May 21, 2022 6:30 UTC (Sat) by developer122 (guest, #152928) [Link] (3 responses)

That saves it to disk, so I guess you could fetch it from the filesystem after rebooting, but the point is really to leave processes in memory and largely unmolested while the OS reboots around them.

Preserving guest memory across kexec

Posted May 21, 2022 12:37 UTC (Sat) by mb (subscriber, #50428) [Link] (2 responses)

Yes. Processes have lots of kernel state that's not easily retained across reboots. That's basically what checkpoint/restore solves.
If you don't want to access the disk, then the only additional thing needed would be a ramdisk that survives reboots where the checkpoints are stored. Such a ramdisk sounds way easier to implement than reinventing checkpoint/restore just for the kexec case.

Preserving guest memory across kexec

Posted May 26, 2022 2:35 UTC (Thu) by developer122 (guest, #152928) [Link]

checkpoint and restore means a ton of copying application data around and packing and unpacking. But I guess you have to do it at all before you can do it zero-copy.

Preserving guest memory across kexec

Posted May 31, 2022 14:51 UTC (Tue) by simcop2387 (subscriber, #101710) [Link]

That actually sounds a lot like a big use case for the whole NVDIMM stuff that has been appearing lately. Faster than disk, not as fast as memory but it's also made to persist between reboots, power offs, etc.