feature: don't do rewrites in rent collection (#26491)

* feature: don't do rewrites in rent collection

* modify test to specifically test this feature

runtime/src/accounts_db.rs

@@ -7612,7 +7612,10 @@ impl AccountsDb {
     /// 1. pubkey, hash pairs for the slot
     /// 2. us spent scanning
     /// 3. Measure started when we began accumulating
-    fn get_pubkey_hash_for_slot(&self, slot: Slot) -> (Vec<(Pubkey, Hash)>, u64, Measure) {
+    pub(crate) fn get_pubkey_hash_for_slot(
+        &self,
+        slot: Slot,
+    ) -> (Vec<(Pubkey, Hash)>, u64, Measure) {
         let mut scan = Measure::start("scan");
 
         let scan_result: ScanStorageResult<(Pubkey, Hash), DashMapVersionHash> = self

runtime/src/bank.rs

@@ -5342,6 +5342,15 @@ impl Bank {
         }
     }
 
+    /// true if rent collection does NOT rewrite accounts whose pubkey indicates
+    ///  it is time for rent collection, but the account is rent exempt.
+    /// false if rent collection DOES rewrite accounts if the account is rent exempt
+    /// This is the default behavior historically.
+    fn bank_hash_skips_rent_rewrites(&self) -> bool {
+        self.feature_set
+            .is_active(&feature_set::skip_rent_rewrites::id())
+    }
+
     /// Collect rent from `accounts`
     ///
     /// This fn is called inside a parallel loop from `collect_rent_in_partition()`.  Avoid adding
@@ -5363,7 +5372,7 @@ impl Bank {
             Vec::<(&Pubkey, &AccountSharedData)>::with_capacity(accounts.len());
         let mut time_collecting_rent_us = 0;
         let mut time_storing_accounts_us = 0;
-        let can_skip_rewrites = false; // this will be goverened by a feature soon
+        let can_skip_rewrites = self.bank_hash_skips_rent_rewrites();
         let set_exempt_rent_epoch_max: bool = self
             .feature_set
             .is_active(&solana_sdk::feature_set::set_exempt_rent_epoch_max::id());
@@ -10046,28 +10055,48 @@ pub(crate) mod tests {
     fn test_collect_rent_from_accounts() {
         solana_logger::setup();
 
-        let zero_lamport_pubkey = Pubkey::new(&[0; 32]);
+        for skip_rewrites in [false, true] {
+            let zero_lamport_pubkey = Pubkey::new(&[0; 32]);
 
-        let genesis_bank = create_simple_test_arc_bank(100000);
-        let first_bank = Arc::new(new_from_parent(&genesis_bank));
-        let first_slot = 1;
-        assert_eq!(first_slot, first_bank.slot());
-        let epoch_delta = 4;
-        let later_bank = Arc::new(new_from_parent_next_epoch(&first_bank, epoch_delta)); // a bank a few epochs in the future
-        let later_slot = later_bank.slot();
-        assert!(later_bank.epoch() == genesis_bank.epoch() + epoch_delta);
+            let genesis_bank = create_simple_test_arc_bank(100000);
+            let mut first_bank = new_from_parent(&genesis_bank);
+            if skip_rewrites {
+                first_bank.activate_feature(&feature_set::skip_rent_rewrites::id());
+            }
+            let first_bank = Arc::new(first_bank);
 
-        let data_size = 0; // make sure we're rent exempt
-        let lamports = later_bank.get_minimum_balance_for_rent_exemption(data_size); // cannot be 0 or we zero out rent_epoch in rent collection and we need to be rent exempt
-        let mut account = AccountSharedData::new(lamports, data_size, &Pubkey::default());
-        account.set_rent_epoch(later_bank.epoch() - 1); // non-zero, but less than later_bank's epoch
+            let first_slot = 1;
+            assert_eq!(first_slot, first_bank.slot());
+            let epoch_delta = 4;
+            let later_bank = Arc::new(new_from_parent_next_epoch(&first_bank, epoch_delta)); // a bank a few epochs in the future
+            let later_slot = later_bank.slot();
+            assert!(later_bank.epoch() == genesis_bank.epoch() + epoch_delta);
 
-        // loaded from previous slot, so we skip rent collection on it
-        let _result = later_bank.collect_rent_from_accounts(
-            vec![(zero_lamport_pubkey, account, later_slot - 1)],
-            None,
-            PartitionIndex::default(),
-        );
+            let data_size = 0; // make sure we're rent exempt
+            let lamports = later_bank.get_minimum_balance_for_rent_exemption(data_size); // cannot be 0 or we zero out rent_epoch in rent collection and we need to be rent exempt
+            let mut account = AccountSharedData::new(lamports, data_size, &Pubkey::default());
+            account.set_rent_epoch(later_bank.epoch() - 1); // non-zero, but less than later_bank's epoch
+
+            // loaded from previous slot, so we skip rent collection on it
+            let _result = later_bank.collect_rent_from_accounts(
+                vec![(zero_lamport_pubkey, account, later_slot - 1)],
+                None,
+                PartitionIndex::default(),
+            );
+
+            let deltas = later_bank
+                .rc
+                .accounts
+                .accounts_db
+                .get_pubkey_hash_for_slot(later_slot)
+                .0;
+            assert_eq!(
+                !deltas
+                    .iter()
+                    .any(|(pubkey, _)| pubkey == &zero_lamport_pubkey),
+                skip_rewrites
+            );
+        }
     }
 
     #[test]

sdk/src/feature_set.rs

@@ -462,6 +462,10 @@ pub mod enable_early_verification_of_account_modifications {
     solana_sdk::declare_id!("7Vced912WrRnfjaiKRiNBcbuFw7RrnLv3E3z95Y4GTNc");
 }
 
+pub mod skip_rent_rewrites {
+    solana_sdk::declare_id!("CGB2jM8pwZkeeiXQ66kBMyBR6Np61mggL7XUsmLjVcrw");
+}
+
 pub mod prevent_crediting_accounts_that_end_rent_paying {
     solana_sdk::declare_id!("812kqX67odAp5NFwM8D2N24cku7WTm9CHUTFUXaDkWPn");
 }
@@ -679,6 +683,7 @@ lazy_static! {
         (stake_redelegate_instruction::id(), "enable the redelegate stake instruction #26294"),
         (preserve_rent_epoch_for_rent_exempt_accounts::id(), "preserve rent epoch for rent exempt accounts #26479"),
         (enable_bpf_loader_extend_program_ix::id(), "enable bpf upgradeable loader ExtendProgram instruction #25234"),
+        (skip_rent_rewrites::id(), "skip rewriting rent exempt accounts during rent collection #26491"),
         (enable_early_verification_of_account_modifications::id(), "enable early verification of account modifications #25899"),
         (disable_rehash_for_rent_epoch::id(), "on accounts hash calculation, do not try to rehash accounts #28934"),
         (account_hash_ignore_slot::id(), "ignore slot when calculating an account hash #28420"),