add --accounts-index-memory-limit-mb (#19269)

runtime/src/accounts_index.rs

@@ -40,11 +40,13 @@ pub const ACCOUNTS_INDEX_CONFIG_FOR_TESTING: AccountsIndexConfig = AccountsIndex
     bins: Some(BINS_FOR_TESTING),
     flush_threads: Some(FLUSH_THREADS_TESTING),
     drives: None,
+    index_limit_mb: None,
 };
 pub const ACCOUNTS_INDEX_CONFIG_FOR_BENCHMARKS: AccountsIndexConfig = AccountsIndexConfig {
     bins: Some(BINS_FOR_BENCHMARKS),
     flush_threads: Some(FLUSH_THREADS_TESTING),
     drives: None,
+    index_limit_mb: None,
 };
 pub type ScanResult<T> = Result<T, ScanError>;
 pub type SlotList<T> = Vec<(Slot, T)>;
@@ -101,6 +103,7 @@ pub struct AccountsIndexConfig {
     pub bins: Option<usize>,
     pub flush_threads: Option<usize>,
     pub drives: Option<Vec<PathBuf>>,
+    pub index_limit_mb: Option<usize>,
 }
 
 #[derive(Debug, Default, Clone)]

runtime/src/bucket_map_holder.rs

@@ -17,6 +17,10 @@ pub struct BucketMapHolder<T: IndexValue> {
     next_bucket_to_flush: Mutex<usize>,
     bins: usize,
 
+    // how much mb are we allowed to keep in the in-mem index?
+    // Rest goes to disk.
+    pub mem_budget_mb: Option<usize>,
+
     /// startup is a special time for flush to focus on moving everything to disk as fast and efficiently as possible
     /// with less thread count limitations. LRU and access patterns are not important. Freeing memory
     /// and writing to disk in parallel are.
@@ -71,7 +75,7 @@ impl<T: IndexValue> BucketMapHolder<T> {
         self.count_ages_flushed.load(Ordering::Relaxed) >= self.bins
     }
 
-    pub fn new(bins: usize, _config: &Option<AccountsIndexConfig>) -> Self {
+    pub fn new(bins: usize, config: &Option<AccountsIndexConfig>) -> Self {
         Self {
             count_ages_flushed: AtomicUsize::default(),
             age: AtomicU8::default(),
@@ -80,6 +84,7 @@ impl<T: IndexValue> BucketMapHolder<T> {
             next_bucket_to_flush: Mutex::new(0),
             bins,
             startup: AtomicBool::default(),
+            mem_budget_mb: config.as_ref().and_then(|config| config.index_limit_mb),
             _phantom: std::marker::PhantomData::<T>::default(),
         }
     }