From 5b481a34a2d364dc85aa128355959c04574508e6 Mon Sep 17 00:00:00 2001
From: jeff washington <jeff.washington@solana.com>
Date: Thu, 20 Jul 2023 13:36:19 -0500
Subject: [PATCH] update lru for read only cache if it has been long enough
 since last access

---
 runtime/src/read_only_accounts_cache.rs | 37 +++++++++++++++++++++----
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/runtime/src/read_only_accounts_cache.rs b/runtime/src/read_only_accounts_cache.rs
index eaa1cd263ace67..e9a8c9a119fb4d 100644
--- a/runtime/src/read_only_accounts_cache.rs
+++ b/runtime/src/read_only_accounts_cache.rs
@@ -8,6 +8,7 @@ use {
         account::{AccountSharedData, ReadableAccount},
         clock::Slot,
         pubkey::Pubkey,
+        timing::timestamp,
     },
     std::sync::{
         atomic::{AtomicU64, AtomicUsize, Ordering},
@@ -23,7 +24,28 @@ type ReadOnlyCacheKey = (Pubkey, Slot);
 #[derive(Debug)]
 struct ReadOnlyAccountCacheEntry {
     account: AccountSharedData,
-    index: Index, // Index of the entry in the eviction queue.
+    /// Index of the entry in the eviction queue.
+    index: Index,
+    /// lower bits of last timestamp when eviction queue was updated
+    last_time: u32,
+}
+
+impl ReadOnlyAccountCacheEntry {
+    fn new(account: AccountSharedData, index: Index) -> Self {
+        Self {
+            account,
+            index,
+            last_time: Self::timestamp(),
+        }
+    }
+    /// lower bits of current timestamp. We don't need higher bits and u32 fits with Index u32
+    fn timestamp() -> u32 {
+        (timestamp() % (u32::MAX as u64 + 1)) as u32
+    }
+    /// ms since `last_time` timestamp
+    fn ms_since_last_time(&self) -> u32 {
+        Self::timestamp().wrapping_sub(self.last_time)
+    }
 }
 
 #[derive(Debug)]
@@ -78,16 +100,19 @@ impl ReadOnlyAccountsCache {
         let (account, load_us) = measure_us!({
             let key = (pubkey, slot);
             let Some(mut entry) = self.cache.get_mut(&key) else {
-            self.misses.fetch_add(1, Ordering::Relaxed);
-            return None;
-        };
+                self.misses.fetch_add(1, Ordering::Relaxed);
+                return None;
+            };
             // Move the entry to the end of the queue.
             // self.queue is modified while holding a reference to the cache entry;
             // so that another thread cannot write to the same key.
-            {
+            // If we updated the eviction queue within this much time, then leave it where it is. We're likely to hit it again.
+            let update_lru = entry.ms_since_last_time() > 500;
+            if update_lru {
                 let mut queue = self.queue.lock().unwrap();
                 queue.remove(entry.index);
                 entry.index = queue.insert_last(key);
+                entry.last_time = ReadOnlyAccountCacheEntry::timestamp();
             }
             let account = entry.account.clone();
             drop(entry);
@@ -113,7 +138,7 @@ impl ReadOnlyAccountsCache {
                 // Insert the entry at the end of the queue.
                 let mut queue = self.queue.lock().unwrap();
                 let index = queue.insert_last(key);
-                entry.insert(ReadOnlyAccountCacheEntry { account, index });
+                entry.insert(ReadOnlyAccountCacheEntry::new(account, index));
             }
             Entry::Occupied(mut entry) => {
                 let entry = entry.get_mut();