The btrfs Wiki glossary says this about what a generation is:

• generation

An internal counter which updates for each transaction. When a metadata block is written (using copy on write), current generation is stored in the block, so that blocks which are too new (and hence possibly inconsistent) can be identified.

Another entry mentions that

Under normal circumstances the generation numbers must match. A mismatch can be caused by a lost write after a crash (ie. a dangling block "pointer"; software bug, hardware bug), misdirected write (the block was never written to that location; software bug, hardware bug).

It doesn't tell me very much, and others are asking too, see for example this mail thread.

Actually, the last post in that thread is mentioning something half useful: A "generation error" is "an indication that blocks have not been written", which is basically echoing what the Wiki says.

So, with that information we can draw some conclusions:

• The btrfs filesystem is not fully documented (user-side) with explanation of the output from its tools (the Wiki even says "For now, most of the information exists in people's heads.")

• There was a few errors writing meta information to disk, which, yes, could indicate a problem.

By answering this question, I hope that some btfs guru pops up and gives you a proper answer to the question "What do I do about it?".

Your next port of call may be asking on an btrfs mailing list, such as the one mentioned in the Wiki (I would do this now if I were you).

The btrfs Wiki glossary says this about what a generation is:

• generation

  An internal counter which updates for each transaction. When a metadata block is written (using copy on write), current generation is stored in the block, so that blocks which are too new (and hence possibly inconsistent) can be identified.

Another entry mentions that

Under normal circumstances the generation numbers must match. A mismatch can be caused by a lost write after a crash (ie. a dangling block "pointer"; software bug, hardware bug), misdirected write (the block was never written to that location; software bug, hardware bug).

It doesn't tell me very much, and others are asking too, see for example this mail thread.

Actually, the last post in that thread is mentioning something half useful: A "generation error" is "an indication that blocks have not been written", which is basically echoing what the Wiki says.

So, with that information we can draw some conclusions:

• The btrfs filesystem is not fully documented (user-side) with explanation of the output from its tools (the Wiki even says "For now, most of the information exists in people's heads.")

• There was a few errors writing meta information to disk, which, yes, could indicate a problem.

By answering this question, I hope that some btfs guru pops up and gives you a proper answer to the question "What do I do about it?".

Your next port of call may be asking on an btrfs mailing list, such as the one mentioned in the Wiki (I would do this now if I were you).