[pve-devel] [PATCH proxmox-backup-qemu 8/9] add shared_cache module
Stefan Reiter
s.reiter at proxmox.com
Wed Jun 2 16:38:32 CEST 2021
Provides a shared AsyncLruCache of 256MB (w/ 4MB chunks) that can be
used by multiple readers at the same time. It is dropped once no more
readers exist, so the memory gets freed if all QEMU block/pbs instances
disappear.
Signed-off-by: Stefan Reiter <s.reiter at proxmox.com>
---
src/lib.rs | 7 ++++++-
src/shared_cache.rs | 36 ++++++++++++++++++++++++++++++++++++
2 files changed, 42 insertions(+), 1 deletion(-)
create mode 100644 src/shared_cache.rs
diff --git a/src/lib.rs b/src/lib.rs
index 05d7b58..aa167f7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -25,6 +25,7 @@ mod restore;
use restore::*;
mod tools;
+mod shared_cache;
pub const PROXMOX_BACKUP_DEFAULT_CHUNK_SIZE: u64 = 1024*1024*4;
@@ -804,7 +805,11 @@ pub extern "C" fn proxmox_restore_connect_async(
pub extern "C" fn proxmox_restore_disconnect(handle: *mut ProxmoxRestoreHandle) {
let restore_task = handle as * mut Arc<RestoreTask>;
- unsafe { Box::from_raw(restore_task) }; //drop(restore_task)
+ let restore_task = unsafe { Box::from_raw(restore_task) };
+ drop(restore_task);
+
+ // after dropping, cache may be unused (if no other handles open)
+ shared_cache::shared_chunk_cache_cleanup();
}
/// Restore an image (sync)
diff --git a/src/shared_cache.rs b/src/shared_cache.rs
new file mode 100644
index 0000000..bebae5b
--- /dev/null
+++ b/src/shared_cache.rs
@@ -0,0 +1,36 @@
+use once_cell::sync::OnceCell;
+use proxmox_backup::backup::ChunkCache;
+use proxmox_backup::tools::async_lru_cache::AsyncLruCache;
+use std::sync::{Arc, Mutex};
+
+const SHARED_CACHE_CAPACITY: usize = 64; // 256 MB
+static SHARED_CACHE: OnceCell<Mutex<Option<ChunkCache>>> = OnceCell::new();
+
+pub fn get_shared_chunk_cache() -> ChunkCache {
+ let mut guard = SHARED_CACHE
+ .get_or_init(|| Mutex::new(None))
+ .lock()
+ .unwrap();
+ match &*guard {
+ Some(cache) => Arc::clone(cache),
+ None => {
+ let cache = Arc::new(AsyncLruCache::new(SHARED_CACHE_CAPACITY));
+ *guard = Some(Arc::clone(&cache));
+ cache
+ }
+ }
+}
+
+pub fn shared_chunk_cache_cleanup() {
+ let mut guard = SHARED_CACHE
+ .get_or_init(|| Mutex::new(None))
+ .lock()
+ .unwrap();
+ if let Some(arc) = guard.as_ref() {
+ let refcount = Arc::strong_count(arc);
+ if refcount == 1 {
+ // no one else is using the cache anymore, drop it
+ let _drop = guard.take();
+ }
+ }
+}
--
2.30.2
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