What if the rent exemption price goes up?

Question

Given that

1. new Solana accounts must be credited - at creation time - with enough SOL to be "rent-exempt",
2. the balance of an account isn't allowed to go below its corresponding minimum "rent-exempt" amount (unless it's being closed - the action that refunds its entire balance),
3. there's no more periodical rent collection performed by the runtime (as of SIMD-0084) and
4. the "rent-exemption" amount (per byte of account data) may change in the future,

What will happen if (or, rather, "when") an increase in the "rent-exemption" amount leads to a part of the accounts no longer having a big-enough SOL balance to remain "rent-exempt" (according to the new, increased price of the exemption)?

Or if, instead of 2y worth of "rent", a 3y worth of it is required by the runtime?

Answer 1

This would be a tough problem to solve, but I think the general idea would be to "grandfather" existing rent-exempt accounts, and only enforce the higher rent-exempt amount for new accounts. We could maybe reuse the rentEpoch field on accounts to know when it's been created, so the runtime could know when the account was created to calculate the "correct" rent-exempt amount.

Most likely, this would never happen though, and instead, Solana would adopt some form of state expiration, similar to Ethereum: https://notes.ethereum.org/@vbuterin/verkle_and_state_expiry_proposal