[pbs-devel] [PATCH proxmox-backup 1/2] tools: lru cache: allow to dynamically increase the cache capacity

[Christian Ebner]

Currently, the capacity of the LRU cache is set at instantiation, not
allowing to change it afterwards. In some situations, e.g. when more
space/memory is available, dynamically increasing it is required.

Therefore, add the methods which allow to increase the capacity by a
given increment, for the lru cache, async lru cache and the local
datastore lru caches, respectively.

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
 pbs-datastore/src/local_datastore_lru_cache.rs | 7 +++++++
 pbs-tools/src/async_lru_cache.rs               | 8 ++++++++
 pbs-tools/src/lru_cache.rs                     | 6 ++++++
 3 files changed, 21 insertions(+)

diff --git a/pbs-datastore/src/local_datastore_lru_cache.rs b/pbs-datastore/src/local_datastore_lru_cache.rs
index c0edd3619..00cce94d6 100644
--- a/pbs-datastore/src/local_datastore_lru_cache.rs
+++ b/pbs-datastore/src/local_datastore_lru_cache.rs
@@ -177,4 +177,11 @@ impl LocalDatastoreLruCache {
     pub fn contains(&self, digest: &[u8; 32]) -> bool {
         self.cache.contains(*digest)
     }
+
+    /// Increases the capacity of the cache by given increment.
+    ///
+    /// Returns the new cache capacity.
+    pub fn increase_capacity(&self, increment: usize) -> usize {
+        self.cache.increase_capacity(increment)
+    }
 }
diff --git a/pbs-tools/src/async_lru_cache.rs b/pbs-tools/src/async_lru_cache.rs
index 3a975de32..dbfa1e21d 100644
--- a/pbs-tools/src/async_lru_cache.rs
+++ b/pbs-tools/src/async_lru_cache.rs
@@ -39,6 +39,14 @@ impl<K: std::cmp::Eq + std::hash::Hash + Copy, V: Clone + Send + 'static> AsyncL
         }
     }
 
+    /// Increment the LRU cache capacity by given increment, saturating at MAX value for usize
+    ///
+    /// Returns the new capacity.
+    pub fn increase_capacity(&self, increment: usize) -> usize {
+        let mut maps = self.maps.lock().unwrap();
+        maps.0.increase_capacity(increment)
+    }
+
     /// Access an item either via the cache or by calling cacher.fetch. A return value of Ok(None)
     /// means the item requested has no representation, Err(_) means a call to fetch() failed,
     /// regardless of whether it was initiated by this call or a previous one.
diff --git a/pbs-tools/src/lru_cache.rs b/pbs-tools/src/lru_cache.rs
index a7aea6528..d12d0675e 100644
--- a/pbs-tools/src/lru_cache.rs
+++ b/pbs-tools/src/lru_cache.rs
@@ -133,6 +133,12 @@ impl<K: std::cmp::Eq + std::hash::Hash + Copy, V> LruCache<K, V> {
         }
     }
 
+    /// Increments the cache capacity by given `increment`, saturating at MAX value for usize
+    pub fn increase_capacity(&mut self, increment: usize) -> usize {
+        self.capacity = self.capacity.saturating_add(increment);
+        self.capacity
+    }
+
     /// Insert or update an entry identified by `key` with the given `value`.
     /// This entry is placed as the most recently used node at the head.
     pub fn insert<F>(&mut self, key: K, value: V, removed: F) -> Result<bool, anyhow::Error>
-- 
2.47.2