[crac] RFR: Support repeated checkpoint and restore operations

[Radim Vansa]

On Thu, 13 Apr 2023 13:37:36 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> * VM option CRaCCheckpointTo is recognized when restoring the application (destination can be changed)
>> * The main problem for checkpoint after restore was old checkpoint image mmapped to files (CRaC-specific CRIU optimization for faster boot). Before performing checkpoint we transparently swap this with memory using anonymous mapping.
>
> src/hotspot/os/linux/os_linux.cpp line 392:
> 
>> 390:       next_checkpoint = "";
>> 391:     }
>> 392:     return write_check_error(fd, next_checkpoint, strlen(next_checkpoint) + 1);
> 
> As CRaCCheckpointTo is not the only option that may require this, we probably want a more generic approach. 
> Like a new option attribute (RESTORE_UPDATEABLE?) 
> 
> https://github.com/openjdk/crac/blob/master/src/hotspot/share/runtime/globals.hpp#L57
> 
> The implementation should check only UPDATEABLE options are provided along -XX:CRaCRestoreFrom.
> 
> This be better done in a separate PR.

I agree we should not mix a complex change like that into this PR. Regarding another option - while a generic way to specify updatable options is a good idea I wouldn't add it to each and every option. Many of those options would need careful analysis if it's possible to make them updatable, so I would rather keep an independent list.

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PR Review Comment: https://git.openjdk.org/crac/pull/57#discussion_r1166471872