Replace mount's per-file cache by a global LRU cache

internal/fuse/blobcache.go

@@ -0,0 +1,87 @@
+package fuse
+
+import (
+	"sync"
+
+	"github.com/restic/restic/internal/debug"
+	"github.com/restic/restic/internal/restic"
+
+	"github.com/hashicorp/golang-lru/simplelru"
+)
+
+// Crude estimate of the overhead per blob: a SHA-256, a linked list node
+// and some pointers. See comment in blobCache.add.
+const cacheOverhead = len(restic.ID{}) + 64
+
+// A blobCache is a fixed-size cache of blob contents.
+// It is safe for concurrent access.
+type blobCache struct {
+	mu sync.Mutex
+	c  *simplelru.LRU
+
+	free, size int // Current and max capacity, in bytes.
+}
+
+// Construct a blob cache that stores at most size bytes worth of blobs.
+func newBlobCache(size int) *blobCache {
+	c := &blobCache{
+		free: size,
+		size: size,
+	}
+
+	// NewLRU wants us to specify some max. number of entries, else it errors.
+	// The actual maximum will be smaller than size/cacheOverhead, because we
+	// evict entries (RemoveOldest in add) to maintain our size bound.
+	maxEntries := size / cacheOverhead
+	lru, err := simplelru.NewLRU(maxEntries, c.evict)
+	if err != nil {
+		panic(err) // Can only be maxEntries <= 0.
+	}
+	c.c = lru
+
+	return c
+}
+
+func (c *blobCache) add(id restic.ID, blob []byte) {
+	debug.Log("blobCache: add %v", id)
+
+	size := len(blob) + cacheOverhead
+	if size > c.size {
+		return
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	var key interface{} = id
+
+	if c.c.Contains(key) { // Doesn't update the recency list.
+		return
+	}
+
+	// This loop takes at most min(maxEntries, maxchunksize/cacheOverhead)
+	// iterations.
+	for size > c.free {
+		c.c.RemoveOldest()
+	}
+
+	c.c.Add(key, blob)
+	c.free -= size
+}
+
+func (c *blobCache) get(id restic.ID) ([]byte, bool) {
+	c.mu.Lock()
+	value, ok := c.c.Get(id)
+	c.mu.Unlock()
+
+	debug.Log("blobCache: get %v, hit %v", id, ok)
+
+	blob, ok := value.([]byte)
+	return blob, ok
+}
+
+func (c *blobCache) evict(key, value interface{}) {
+	blob := value.([]byte)
+	debug.Log("blobCache: evict %v, %d bytes", key, len(blob))
+	c.free += len(blob) + cacheOverhead
+}