"PKRAM" Revived For Preserving Memory Pages Across Kexec'ing Kernels

Written by Michael Larabel in Oracle on 31 March 2021 at 02:30 AM EDT. Add A Comment
Patches back in 2013 were proposed for "PRAM" as persistent over-kexec memory storage to allow saving of memory pages across kernel reboots via kexec or when hitting a new kernel via kexec. Nearly one year ago Oracle retook up the effort and sent out PKRAM as their "preserved-over-Kexec" RAM and now finally a second iteration of PKRAM has been published.

PKRAM remains focused on providing the ability to save memory pages of the currently running kernel so that those pages can be restored after a kexecc into a new kernel.

Among the use-cases being eyed for PKRAM if/when the work is mainlined is being able to preserve guest memory or select data for VMM Fast Restart to speed-up the reboot process into new kernels, primarily for enterprise environments where keeping downtime to a minimum is much preferred and PKRAM would allow preserving the state across "reboots" under kexec. Also PKRAM is being evaluated for database servers to preserve shared memory block caches across reboots.

Compared to the PKRAM code sent out last May, the new patch series -- 43 patches in total -- is re-based against the latest Linux 5.12 code, the API has been improved upon, and various other design improvements. With the patches the PKRAM kernel API is tapped into by Tmpfs as a means of allowing Tmpfs files to be preserved across Kexec as a clean example.

These PKRAM v2 patches are under review now on the kernel mailing list. We'll see how this round goes and see if the feature finally is able to be mainlined in the not too distant future.
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