[TieredStorage] Allow HotStorage to handle more account data (solana-…

…labs#34155)

#### Problem
After we have defined AccountOffset to be u32, it means the address space within
one HotAccountsFile is up to 4GB.  However, since the Accounts Blocks in a
HotAccountsFile is 8-byte aligned, it has the opportunity to store more data by
internally multiplying the AccountOffset by 8.

#### Summary of Changes
This PR allows a HotAccountsFile to store up to 32GB accounts data by using
8 x AccountOffset as its actual offset.

#### Test Plan
Updated existing unit-tests.

accounts-db/src/tiered_storage/hot.rs

@@ -36,6 +36,10 @@ const MAX_HOT_PADDING: u8 = 7;
 /// The maximum allowed value for the owner index of a hot account.
 const MAX_HOT_OWNER_OFFSET: OwnerOffset = OwnerOffset((1 << 29) - 1);
 
+/// The multiplier for converting AccountOffset to the internal hot account
+/// offset.  This increases the maximum size of a hot accounts file.
+const HOT_ACCOUNT_OFFSET_MULTIPLIER: usize = 8;
+
 #[bitfield(bits = 32)]
 #[repr(C)]
 #[derive(Debug, Default, Copy, Clone, Eq, PartialEq)]
@@ -228,7 +232,9 @@ impl HotStorageReader {
         &self,
         account_offset: AccountOffset,
     ) -> TieredStorageResult<&HotAccountMeta> {
-        let (meta, _) = get_type::<HotAccountMeta>(&self.mmap, account_offset.block as usize)?;
+        let internal_account_offset = account_offset.block as usize * HOT_ACCOUNT_OFFSET_MULTIPLIER;
+
+        let (meta, _) = get_type::<HotAccountMeta>(&self.mmap, internal_account_offset)?;
         Ok(meta)
     }
 
@@ -468,7 +474,10 @@ pub mod tests {
                 .map(|meta| {
                     let prev_offset = current_offset;
                     current_offset += file.write_type(meta).unwrap() as u32;
-                    AccountOffset { block: prev_offset }
+                    assert_eq!(prev_offset % HOT_ACCOUNT_OFFSET_MULTIPLIER as u32, 0);
+                    AccountOffset {
+                        block: prev_offset / HOT_ACCOUNT_OFFSET_MULTIPLIER as u32,
+                    }
                 })
                 .collect();
             // while the test only focuses on account metas, writing a footer