Hold read lock during startup shrink (#17309)

* hold read lock during account scan of shrink

* rename and improve rusty

runtime/src/accounts_db.rs

@@ -1911,7 +1911,7 @@ impl AccountsDb {
         );
     }
 
-    fn do_shrink_slot_stores<'a, I>(&'a self, slot: Slot, stores: I)
+    fn do_shrink_slot_stores<'a, I>(&'a self, slot: Slot, stores: I, is_startup: bool)
     where
         I: Iterator<Item = &'a Arc<AccountStorageEntry>>,
     {
@@ -1950,31 +1950,47 @@ impl AccountsDb {
 
         let mut index_read_elapsed = Measure::start("index_read_elapsed");
         let mut alive_total = 0;
-        let alive_accounts: Vec<_> = {
-            stored_accounts
-                .iter()
-                .filter(|(pubkey, stored_account)| {
-                    if let Some(locked_entry) = self.accounts_index.get_account_read_entry(pubkey) {
-                        let is_alive = locked_entry.slot_list().iter().any(|(_slot, i)| {
-                            i.store_id == stored_account.store_id
-                                && i.offset == stored_account.account.offset
-                        });
-                        if !is_alive {
-                            // This pubkey was found in the storage, but no longer exists in the index.
-                            // It would have had a ref to the storage from the initial store, but it will
-                            // not exist in the re-written slot. Unref it to keep the index consistent with
-                            // rewriting the storage entries.
-                            locked_entry.unref()
-                        } else {
-                            alive_total += stored_account.account_size as u64;
-                        }
-                        is_alive
+        let accounts_index_map_lock = if is_startup {
+            // at startup, there is nobody else to contend with the accounts_index read lock, so it is more efficient for us to keep it held
+            Some(self.accounts_index.get_account_maps_read_lock())
+        } else {
+            None
+        };
+        let accounts_index_map_lock_ref = accounts_index_map_lock.as_ref();
+
+        let alive_accounts: Vec<_> = stored_accounts
+            .iter()
+            .filter(|(pubkey, stored_account)| {
+                let lookup = if is_startup {
+                    self.accounts_index.get_account_read_entry_with_lock(
+                        pubkey,
+                        accounts_index_map_lock_ref.unwrap(),
+                    )
+                } else {
+                    self.accounts_index.get_account_read_entry(pubkey)
+                };
+
+                if let Some(locked_entry) = lookup {
+                    let is_alive = locked_entry.slot_list().iter().any(|(_slot, i)| {
+                        i.store_id == stored_account.store_id
+                            && i.offset == stored_account.account.offset
+                    });
+                    if !is_alive {
+                        // This pubkey was found in the storage, but no longer exists in the index.
+                        // It would have had a ref to the storage from the initial store, but it will
+                        // not exist in the re-written slot. Unref it to keep the index consistent with
+                        // rewriting the storage entries.
+                        locked_entry.unref()
                     } else {
-                        false
+                        alive_total += stored_account.account_size as u64;
                     }
-                })
-                .collect()
-        };
+                    is_alive
+                } else {
+                    false
+                }
+            })
+            .collect();
+        drop(accounts_index_map_lock);
         index_read_elapsed.stop();
         let aligned_total: u64 = self.page_align(alive_total);
 
@@ -2136,7 +2152,7 @@ impl AccountsDb {
 
     // Reads all accounts in given slot's AppendVecs and filter only to alive,
     // then create a minimum AppendVec filled with the alive.
-    fn shrink_slot_forced(&self, slot: Slot) -> usize {
+    fn shrink_slot_forced(&self, slot: Slot, is_startup: bool) -> usize {
         debug!("shrink_slot_forced: slot: {}", slot);
 
         if let Some(stores_lock) = self.storage.get_slot_stores(slot) {
@@ -2157,7 +2173,7 @@ impl AccountsDb {
                 );
                 return 0;
             }
-            self.do_shrink_slot_stores(slot, stores.iter());
+            self.do_shrink_slot_stores(slot, stores.iter(), is_startup);
             alive_count
         } else {
             0
@@ -2177,7 +2193,7 @@ impl AccountsDb {
         let num_candidates = shrink_slots.len();
         for (slot, slot_shrink_candidates) in shrink_slots {
             let mut measure = Measure::start("shrink_candidate_slots-ms");
-            self.do_shrink_slot_stores(slot, slot_shrink_candidates.values());
+            self.do_shrink_slot_stores(slot, slot_shrink_candidates.values(), false);
             measure.stop();
             inc_new_counter_info!("shrink_candidate_slots-ms", measure.as_ms() as usize);
         }
@@ -2190,13 +2206,13 @@ impl AccountsDb {
             let chunk_size = std::cmp::max(slots.len() / 8, 1); // approximately 400k slots in a snapshot
             slots.par_chunks(chunk_size).for_each(|slots| {
                 for slot in slots {
-                    self.shrink_slot_forced(*slot);
+                    self.shrink_slot_forced(*slot, is_startup);
                 }
             });
         } else {
             for slot in self.all_slots_in_storage() {
                 if self.caching_enabled {
-                    self.shrink_slot_forced(slot);
+                    self.shrink_slot_forced(slot, false);
                 } else {
                     self.do_shrink_slot_forced_v1(slot);
                 }

runtime/src/accounts_index.rs

@@ -838,10 +838,16 @@ impl<T: 'static + Clone + IsCached + ZeroLamport> AccountsIndex<T> {
     }
 
     pub fn get_account_read_entry(&self, pubkey: &Pubkey) -> Option<ReadAccountMapEntry<T>> {
-        self.account_maps
-            .read()
-            .unwrap()
-            .get(pubkey)
+        let lock = self.get_account_maps_read_lock();
+        self.get_account_read_entry_with_lock(pubkey, &lock)
+    }
+
+    pub fn get_account_read_entry_with_lock(
+        &self,
+        pubkey: &Pubkey,
+        lock: &AccountMapsReadLock<'_, T>,
+    ) -> Option<ReadAccountMapEntry<T>> {
+        lock.get(pubkey)
             .cloned()
             .map(ReadAccountMapEntry::from_account_map_entry)
     }
@@ -1184,6 +1190,10 @@ impl<T: 'static + Clone + IsCached + ZeroLamport> AccountsIndex<T> {
         self.account_maps.write().unwrap()
     }
 
+    pub(crate) fn get_account_maps_read_lock(&self) -> AccountMapsReadLock<T> {
+        self.account_maps.read().unwrap()
+    }
+
     // Same functionally to upsert, but:
     // 1. operates on a batch of items
     // 2. holds the write lock for the duration of adding the items
@@ -2411,8 +2421,21 @@ pub mod tests {
         }
         assert!(gc.is_empty());
 
-        {
-            let entry = index.get_account_read_entry(&key).unwrap();
+        for lock in &[false, true] {
+            let read_lock = if *lock {
+                Some(index.get_account_maps_read_lock())
+            } else {
+                None
+            };
+
+            let entry = if *lock {
+                index
+                    .get_account_read_entry_with_lock(&key, read_lock.as_ref().unwrap())
+                    .unwrap()
+            } else {
+                index.get_account_read_entry(&key).unwrap()
+            };
+
             assert_eq!(
                 entry.ref_count().load(Ordering::Relaxed),
                 if is_cached { 0 } else { 2 }