Supporting a lookup structure for a file system implementing hierarchical reference counting

A non-transitory machine readable medium comprising instructions, which when executed by a machine, causes the machine to:

• in response to receiving a snapshot restore operation to restore a file system implementing hierarchical reference counting for pages within storage to a state captured by a snapshot, traverse a lookup structure to invalidate lookup entries that have entry generation counts greater than a file system info generation count of the snapshot;
• and
• in response traversing the lookup structure to invalidate the lookup entries, utilize the lookup structure to restore the file system to the state captured by the snapshot as a restored file system;
• and
• process access to a file within the restored file system by:
• in response to identifying a mismatch between a lookup entry clone generation count of a lookup entry for the file and an inode generation count of an inode for the file, invalidating the lookup entry as being unusable and performing a file system tree traversal to identify an accurate reference count for providing the access to the file.

A computing device implementing a node comprising:

• a memory comprising machine executable code;
• and
• a processor coupled to the memory, the processor configured to execute the machine executable code to cause the computing device to:
• create a snapshot of a file system implementing hierarchical reference counting for pages within storage;
• receive a snapshot restore operation to restore the file system to a state captured by the snapshot;
• traverse a lookup structure to invalidate lookup entries that have entry generation counts greater than a file system info generation count of the snapshot;
• and
• in response traversing the lookup structure to invalidate the lookup entries, utilize the lookup structure to restore the file system to the state captured by the snapshot as a restored file system;
• and
• process access to a file of the restored file system by:
• in response to identifying a match between a lookup entry clone generation count of a lookup entry for the file and an inode generation count of an inode for the file, utilizing the lookup entry to directly access a page storing the file;
• and
• in response to identifying a mismatch between the lookup entry clone generation count and the inode generation count, invalidating the lookup entry as being unusable and performing a file system tree traversal to identify an accurate reference count for providing access to the file.