Implement LRU cache (#150)

core/Cargo.toml

@@ -45,7 +45,6 @@ starry-process.workspace = true
 starry-signal.workspace = true
 starry-vm.workspace = true
 strum = { version = "0.27.2", default-features = false, features = ["derive"] }
-uluru = "3.1.0"
 weak-map = "0.1.1"
 xmas-elf = "0.9"
 

core/src/lib.rs

@@ -12,6 +12,7 @@ extern crate axlog;
 
 pub mod config;
 pub mod futex;
+mod lrucache;
 pub mod mm;
 pub mod resources;
 pub mod shm;

core/src/lrucache.rs

@@ -0,0 +1,187 @@
+use alloc::vec::Vec;
+use core::mem::replace;
+
+/// A simple LRU Cache implementation based on a fixed-size array.
+///
+/// It maintains a fixed-capacity storage and uses an intrusive doubly-linked list
+/// structure using array indices to track the usage order (from MRU to LRU).
+#[derive(Debug, Clone)]
+pub struct LruCache<V, const CAP: usize> {
+    storage: Vec<CacheNode<V>>,
+    mru_idx: u16,
+    lru_idx: u16,
+}
+
+/// Internal node for the LRU cache linked list.
+#[derive(Debug, Clone)]
+struct CacheNode<V> {
+    payload: V,
+    prev: u16,
+    next: u16,
+}
+
+impl<V, const CAP: usize> Default for LruCache<V, CAP> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<V, const CAP: usize> LruCache<V, CAP> {
+    /// Creates a new empty LRU cache.
+    pub const fn new() -> Self {
+        Self {
+            storage: Vec::new(),
+            mru_idx: 0,
+            lru_idx: 0,
+        }
+    }
+
+    /// Inserts a value into the cache.
+    ///
+    /// The inserted value becomes the most-recently-used (MRU) item.
+    /// If the cache is full, the least-recently-used (LRU) item is removed and returned.
+    pub fn put(&mut self, val: V) -> Option<V> {
+        let node = CacheNode {
+            payload: val,
+            prev: 0,
+            next: 0,
+        };
+
+        if self.storage.len() >= CAP {
+            let idx = self.pop_lru();
+            let old = replace(&mut self.storage[idx as usize], node);
+            self.push_mru(idx);
+            Some(old.payload)
+        } else {
+            let idx = self.storage.len() as u16;
+            self.storage.push(node);
+            self.push_mru(idx);
+            None
+        }
+    }
+
+    /// Accesses an item in the cache that matches the predicate.
+    ///
+    /// If an item is found, it is promoted to the most-recently-used (MRU) position,
+    /// and the function returns `true`. Otherwise, it returns `false`.
+    pub fn access<F>(&mut self, mut pred: F) -> bool
+    where
+        F: FnMut(&V) -> bool,
+    {
+        for i in 0..self.storage.len() {
+            if pred(&self.storage[i].payload) {
+                self.promote(i as u16);
+                return true;
+            }
+        }
+        false
+    }
+
+    /// Returns a reference to the most-recently-used (MRU) item.
+    ///
+    /// This does not change the cache state.
+    pub fn peek_mru(&self) -> Option<&V> {
+        self.storage.get(self.mru_idx as usize).map(|n| &n.payload)
+    }
+
+    /// Returns an iterator over the cache items, ordered from MRU to LRU.
+    pub fn items(&self) -> LruIter<'_, V, CAP> {
+        LruIter::<V, CAP> {
+            cache: self,
+            pos: self.mru_idx,
+        }
+    }
+
+    /// Clears all items from the cache.
+    pub fn flush(&mut self) {
+        self.storage.clear();
+        self.mru_idx = 0;
+        self.lru_idx = 0;
+    }
+
+    fn promote(&mut self, idx: u16) {
+        if idx != self.mru_idx {
+            self.unlink(idx);
+            self.push_mru(idx);
+        }
+    }
+
+    fn unlink(&mut self, idx: u16) {
+        let prev = self.storage[idx as usize].prev;
+        let next = self.storage[idx as usize].next;
+
+        if idx == self.mru_idx {
+            self.mru_idx = next;
+        } else {
+            self.storage[prev as usize].next = next;
+        }
+
+        if idx == self.lru_idx {
+            self.lru_idx = prev;
+        } else {
+            self.storage[next as usize].prev = prev;
+        }
+    }
+
+    fn push_mru(&mut self, idx: u16) {
+        if self.storage.len() == 1 {
+            self.lru_idx = idx;
+        } else {
+            self.storage[idx as usize].next = self.mru_idx;
+            self.storage[self.mru_idx as usize].prev = idx;
+        }
+        self.mru_idx = idx;
+    }
+
+    fn pop_lru(&mut self) -> u16 {
+        let idx = self.lru_idx;
+
+        if self.storage.len() <= 1 {
+            // Single-element cache: after popping, there is no valid MRU/LRU.
+            // Reset indices; the caller is expected to reuse `idx` as needed.
+            self.mru_idx = 0;
+            self.lru_idx = 0;
+        } else {
+            let prev = self.storage[idx as usize].prev;
+            // The previous node becomes the new LRU (tail).
+            self.lru_idx = prev;
+            // Fully unlink the old LRU by clearing the new tail's `next`
+            // pointer so it no longer points at the removed node.
+            self.storage[prev as usize].next = prev;
+        }
+        idx
+    }
+}
+
+/// Iterator over the `LruCache` items, from MRU to LRU.
+pub struct LruIter<'a, V, const CAP: usize> {
+    cache: &'a LruCache<V, CAP>,
+    pos: u16,
+}
+
+impl<'a, V, const CAP: usize> Iterator for LruIter<'a, V, CAP> {
+    type Item = &'a V;
+
+    fn next(&mut self) -> Option<&'a V> {
+        // Ensure CAP fits in u16, as indices are u16.
+        const _: () = assert!(CAP <= u16::MAX as usize, "CAP must fit in u16");
+
+        if self.cache.storage.is_empty() {
+            return None;
+        }
+        if self.pos as usize >= self.cache.storage.len() {
+            return None;
+        }
+
+        let node = &self.cache.storage[self.pos as usize];
+        let val = &node.payload;
+
+        let current_pos = self.pos;
+        if current_pos == self.cache.lru_idx {
+            self.pos = CAP as u16;
+        } else {
+            self.pos = node.next;
+        }
+        Some(val)
+    }
+}

core/src/mm.rs

@@ -20,10 +20,10 @@ use kernel_guard::IrqSave;
 use memory_addr::{MemoryAddr, PAGE_SIZE_4K, VirtAddr};
 use ouroboros::self_referencing;
 use starry_vm::{VmError, VmIo, VmResult};
-use uluru::LRUCache;
 
 use crate::{
     config::{USER_SPACE_BASE, USER_SPACE_SIZE},
+    lrucache::LruCache,
     task::AsThread,
 };
 
@@ -173,22 +173,22 @@ impl ElfCacheEntry {
     }
 }
 
-struct ElfLoader(LRUCache<ElfCacheEntry, 32>);
+struct ElfLoader(LruCache<ElfCacheEntry, 32>);
 
 type LoadResult = Result<(VirtAddr, Vec<AuxEntry>), Vec<u8>>;
 
 impl ElfLoader {
     const fn new() -> Self {
-        Self(LRUCache::new())
+        Self(LruCache::new())
     }
 
     fn load(&mut self, uspace: &mut AddrSpace, path: &str) -> AxResult<LoadResult> {
         let loc = FS_CONTEXT.lock().resolve(path)?;
 
-        if !self.0.touch(|e| e.borrow_cache().location().ptr_eq(&loc)) {
+        if !self.0.access(|e| e.borrow_cache().location().ptr_eq(&loc)) {
             match ElfCacheEntry::load(loc)? {
                 Ok(e) => {
-                    self.0.insert(e);
+                    self.0.put(e);
                 }
                 Err(data) => {
                     return Ok(Err(data));
@@ -199,7 +199,7 @@ impl ElfLoader {
         uspace.clear();
         map_trampoline(uspace)?;
 
-        let entry = self.0.front().unwrap();
+        let entry = self.0.peek_mru().unwrap();
         let ldso = if let Some(header) = entry
             .borrow_elf()
             .ph
@@ -223,12 +223,12 @@ impl ElfLoader {
 
         let (elf, ldso) = if let Some(ldso) = ldso {
             let loc = FS_CONTEXT.lock().resolve(ldso)?;
-            if !self.0.touch(|e| e.borrow_cache().location().ptr_eq(&loc)) {
+            if !self.0.access(|e| e.borrow_cache().location().ptr_eq(&loc)) {
                 let e = ElfCacheEntry::load(loc)?.map_err(|_| AxError::InvalidInput)?;
-                self.0.insert(e);
+                self.0.put(e);
             }
 
-            let mut iter = self.0.iter();
+            let mut iter = self.0.items();
             let ldso = iter.next().unwrap();
             let elf = iter.next().unwrap();
             (elf, Some(ldso))
@@ -259,7 +259,7 @@ static ELF_LOADER: Mutex<ElfLoader> = Mutex::new(ElfLoader::new());
 ///
 /// Useful for removing noises during memory leak detect.
 pub fn clear_elf_cache() {
-    ELF_LOADER.lock().0.clear();
+    ELF_LOADER.lock().0.flush();
 }
 
 /// Load the user app to the user address space.