Oracle Working On "PKRAM" For Memory That Survives After Booting Into A New Kexec Kernel
Written by Michael Larabel in Oracle on 8 May 2020 at 03:33 AM EDT. 1 Comment
Oracle's Anthony Yznaga has sent out a proposal for "PKRAM" as a new means of being able to preserve memory pages of the currently running kernel so that they can be restored after launching a new kernel via kexec.

One of the mentioned use-cases for "Preserved-over-Kexec RAM" is preserving guest memory of virtual machines across kexec boots in order to support the Intel proposed VMM Fast Restart. VMM Fast Restart laid out by Intel last year would be using Kexec reboots to avoid system firmware time, seamless guest state saving, and re-using other kernel mappings to save time.

Another use-case brought up by the Oracle engineer would be preserving block caches for database servers stored in shared memory across (kexec-based) reboots.

This PKRAM proposal is just in regards to Kexec usage for this system call that allows booting another kernel from the currently running kernel. Kexec-based execution is increasingly common in the server space to avoid the downtime from the BIOS/UEFI boot/initialization process and others trying to keep system downtime to an absolute minimum.

The 43 patches are based on earlier work from 2013 for "PRAM" as a means of persistent memory storage over kexec. That work wasn't merged but now Oracle is going through with this PKRAM proposal.

With these "request for comments" patches, PKRAM is wired into TMPFS as an example for allowing TMPFS files to be preserved across kexec-ed kernels. We'll see where this Preserved-over-Kexec RAM proposal leads.
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