Synchronous management of disk flush requests

A method comprising:

• recording, by a virtual machine monitor executed by a host computer, a source-generation count representing contents on a source disk associated with a virtual machine;
• recording a writes-mirrored value representing content on a destination disk migrated from a source disk, at a time contents of the source disk and the destination disk were equal;
• recording a flush-request value representing the source-generation count at a time a flush is requested by a guest operating system of a virtual machine;
• recording a writes-flushed value representing the writes-mirrored value at a time of a last flush of the destination disk;
• determining that the flush-request value is less than or equal to the writes-flushed value or the flush-request value is greater than or equal to the source-generation count;
• setting the flush-request value to the source-generation count;
• and
• reporting confirmation of completion of the flush request upon determining that the writes-flushed value is greater than or equal to the source-generation count.

A non-transitory computer readable storage medium including instructions that, when executed by a processing device, cause the processing device to perform operations comprising:

• recording, by a virtual machine monitor executed by the processing device, a source-generation count representing contents on a source disk associated with a virtual machine;
• recording a writes-mirrored value representing content on a destination disk migrated from a source disk, at a time contents of the source disk and the destination disk were equal;
• recording a flush-request value representing the source-generation count at a time a flush is requested by a guest operating system of the virtual machine;
• recording a writes-flushed value representing the writes-mirrored value at a time of a last flush of the destination disk;
• identifying, by the virtual machine monitor, a steady state wherein contents associated with a virtual machine stored on the source disk and a destination disk are equal;
• upon identifying the steady state, setting a writes-mirrored value to the recorded source-generation count;
• determining if a flush request to flush the source disk has been issued by the guest operating system of the virtual machine;
• setting the flush-request value to the source-generation count at a time of the flush request;
• and
• flushing the destination disk upon determining that the flush-request value is greater than the writes-flushed value and the flush-request value is less than or equal to the writes-mirrored value.

A system comprising:

• a memory;
• a processing device, coupled to the memory, the processing device to perform operations comprising:
• recording, by a virtual machine monitor executed by the processing device, a source-generation count representing contents on a source disk associated with a virtual machine;
• recording a writes-mirrored value representing content on a destination disk migrated from a source disk, at a time contents of the source disk and the destination disk were equal;
• recording a flush-request value representing the source-generation count at a time a flush is requested by a guest operating system of the virtual machine;
• recording a writes-flushed value representing the writes-mirrored value at a time of a last flush of the destination disk;
• identifying, by the virtual machine monitor, a steady state wherein contents associated with a virtual machine stored on the source disk and a destination disk are equal;
• upon identifying the steady state, setting a writes-mirrored value to the recorded source-generation count;
• determining if a flush request to flush the source disk has been issued by the guest operating system of the virtual machine;
• setting the flush-request value to the source-generation count at a time of the flush request;
• and
• flushing the destination disk upon determining that the flush-request value is greater than the writes-flushed value and the flush-request value is less than or equal to the writes-mirrored value.