feat: disable partitioned rent collection

[jstarry]

Problem

Implement SIMD-0175 (Amended in solana-foundation/solana-improvement-documents#230)

Summary of Changes

Adds new feature gate to conditionally not run partitioned rent collection

Feature Gate Issue: #4562

[brooksprumo]

Here in the SVM code, if partitioned rent collection is disabled, should we skip updating the rent_epoch?

agave/svm/src/account_loader.rs

Lines 245 to 273 in 8263936

	/// Collect rent from an account if rent is still enabled and regardless of
	/// whether rent is enabled, set the rent epoch to u64::MAX if the account is
	/// rent exempt.
	pub fn collect_rent_from_account(
	feature_set: &FeatureSet,
	rent_collector: &dyn SVMRentCollector,
	address: &Pubkey,
	account: &mut AccountSharedData,
	) -> CollectedInfo {
	if !feature_set.is_active(&feature_set::disable_rent_fees_collection::id()) {
	rent_collector.collect_rent(address, account)
	} else {
	// When rent fee collection is disabled, we won't collect rent for any account. If there
	// are any rent paying accounts, their `rent_epoch` won't change either. However, if the
	// account itself is rent-exempted but its `rent_epoch` is not u64::MAX, we will set its
	// `rent_epoch` to u64::MAX. In such case, the behavior stays the same as before.
	if account.rent_epoch() != RENT_EXEMPT_RENT_EPOCH
	&& rent_collector.get_rent_due(
	account.lamports(),
	account.data().len(),
	account.rent_epoch(),
	) == RentDue::Exempt
	{
	account.set_rent_epoch(RENT_EXEMPT_RENT_EPOCH);
	}
	CollectedInfo::default()
	}
	}

My understanding is when the feature is enabled that we should stop modifying any account's rent_epoch field.

[jstarry]

My understanding is when the feature is enabled that we should stop modifying any account's rent_epoch field.

We could do that but I didn't mention this in the SIMD amendment at all. We still set the rent_epoch to a non default value for new accounts as well. How about we amend the SIMD again to be explicitly about not updating the rent_epoch anymore (including for new accounts)? By doing that, we can still remove partitioned rent collection completely. Seems like a better way to clean things up.

[brooksprumo]

We could do that but I didn't mention this in the SIMD amendment at all.

Yes, you're right. I went back and reread the SIMD and see only rent collection during bank freeze is called out.

We still set the rent_epoch to a non default value for new accounts as well. How about we amend the SIMD again to be explicitly about not updating the rent_epoch anymore (including for new accounts)? By doing that, we can still remove partitioned rent collection completely. Seems like a better way to clean things up.

Works for me! I found it unexpected that we still did rent collection for accounts loaded during transaction processing. I do like the idea of removing rent collection everywhere.

[HaoranYi]

Just to be clear. There are two kinds of rent collections. (a) partitioned
rent collection and (2) individual rent collection.

This SIMD only deals with partitioned rent collection, which is fine, because
most of the gain from disabling rent collection is in (a).

We can leave 'individual rent collection' as it is for future works.

[brooksprumo]

We can leave 'individual rent collection' as it is for future works.

Yeah, we could do it separate, but then we'd need another SIMD and another feature gate.

[HaoranYi]

Yeah, we could do it separate, but then we'd need another SIMD and another feature gate.

Then it become a question of how complex it is to disable individual accounts rent collection? Is it complex enough to justify the cost to write a new SIMD and new feature gate?