On Wed, Jun 02, 2021 at 04:38:32PM +0200, Stefan Reiter wrote:
> 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.rei...@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();
OnceCell *and* Option is a bit too much, `get_shared_chunk_chache()` can
just initialize it in `get_or_init()` directly.
> +
> +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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