From: Stefan Reiter <s.reiter@proxmox.com>
To: pve-devel@lists.proxmox.com, pbs-devel@lists.proxmox.com
Subject: [pve-devel] [PATCH v2 proxmox-backup 3/9] backup: add CachedChunkReader utilizing AsyncLruCache
Date: Mon, 7 Jun 2021 17:35:26 +0200 [thread overview]
Message-ID: <20210607153532.2522267-4-s.reiter@proxmox.com> (raw)
In-Reply-To: <20210607153532.2522267-1-s.reiter@proxmox.com>
Provides a fast arbitrary read implementation with full async and
concurrency support.
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---
This is technically all that's needed for proxmox-backup-qemu to build and
function as intended, but I decided to also use this IMHO cleaner implementation
to replace the AsyncIndexReader with the following patches.
v2:
* drop ChunkCache type alias, not necessary and looked weird, since it couldn't
be constructed directly
* add comment to other unwrap in read_at
src/backup.rs | 3 ++
src/backup/cached_chunk_reader.rs | 89 +++++++++++++++++++++++++++++++
2 files changed, 92 insertions(+)
create mode 100644 src/backup/cached_chunk_reader.rs
diff --git a/src/backup.rs b/src/backup.rs
index ae937be0..5e1147b4 100644
--- a/src/backup.rs
+++ b/src/backup.rs
@@ -259,3 +259,6 @@ pub use catalog_shell::*;
mod async_index_reader;
pub use async_index_reader::*;
+
+mod cached_chunk_reader;
+pub use cached_chunk_reader::*;
diff --git a/src/backup/cached_chunk_reader.rs b/src/backup/cached_chunk_reader.rs
new file mode 100644
index 00000000..ff476e37
--- /dev/null
+++ b/src/backup/cached_chunk_reader.rs
@@ -0,0 +1,89 @@
+//! An async and concurrency safe data reader backed by a local LRU cache.
+
+use anyhow::Error;
+
+use std::future::Future;
+use std::sync::Arc;
+
+use crate::backup::{AsyncReadChunk, IndexFile};
+use crate::tools::async_lru_cache::{AsyncCacher, AsyncLruCache};
+
+struct AsyncChunkCacher<T> {
+ reader: Arc<T>,
+}
+
+impl<T: AsyncReadChunk + Send + Sync + 'static> AsyncCacher<[u8; 32], Arc<Vec<u8>>>
+ for AsyncChunkCacher<T>
+{
+ fn fetch(
+ &self,
+ key: [u8; 32],
+ ) -> Box<dyn Future<Output = Result<Option<Arc<Vec<u8>>>, Error>> + Send> {
+ let reader = Arc::clone(&self.reader);
+ Box::new(async move {
+ AsyncReadChunk::read_chunk(reader.as_ref(), &key)
+ .await
+ .map(|x| Some(Arc::new(x)))
+ })
+ }
+}
+
+/// Allows arbitrary data reads from an Index via an AsyncReadChunk implementation, using an LRU
+/// cache internally to cache chunks and provide support for multiple concurrent reads (potentially
+/// to the same chunk).
+pub struct CachedChunkReader<I: IndexFile, R: AsyncReadChunk + Send + Sync + 'static> {
+ cache: Arc<AsyncLruCache<[u8; 32], Arc<Vec<u8>>>>,
+ cacher: AsyncChunkCacher<R>,
+ index: I,
+}
+
+impl<I: IndexFile, R: AsyncReadChunk + Send + Sync + 'static> CachedChunkReader<I, R> {
+ /// Create a new reader with a local LRU cache containing 'capacity' chunks.
+ pub fn new(reader: R, index: I, capacity: usize) -> Self {
+ let cache = Arc::new(AsyncLruCache::new(capacity));
+ Self::new_with_cache(reader, index, cache)
+ }
+
+ /// Create a new reader with a custom LRU cache. Use this to share a cache between multiple
+ /// readers.
+ pub fn new_with_cache(
+ reader: R,
+ index: I,
+ cache: Arc<AsyncLruCache<[u8; 32], Arc<Vec<u8>>>>,
+ ) -> Self {
+ Self {
+ cache,
+ cacher: AsyncChunkCacher {
+ reader: Arc::new(reader),
+ },
+ index,
+ }
+ }
+
+ /// Read data at a given byte offset into a variable size buffer. Returns the amount of bytes
+ /// read, which will always be the size of the buffer except when reaching EOF.
+ pub async fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize, Error> {
+ let size = buf.len();
+ let mut read: usize = 0;
+ while read < size {
+ let cur_offset = offset + read as u64;
+ if let Some(chunk) = self.index.chunk_from_offset(cur_offset) {
+ // chunk indices retrieved from chunk_from_offset always resolve to Some(_)
+ let info = self.index.chunk_info(chunk.0).unwrap();
+
+ // will never be None, see AsyncChunkCacher
+ let data = self.cache.access(info.digest, &self.cacher).await?.unwrap();
+
+ let want_bytes = ((info.range.end - cur_offset) as usize).min(size - read);
+ let slice = &mut buf[read..(read + want_bytes)];
+ let intra_chunk = chunk.1 as usize;
+ slice.copy_from_slice(&data[intra_chunk..(intra_chunk + want_bytes)]);
+ read += want_bytes;
+ } else {
+ // EOF
+ break;
+ }
+ }
+ Ok(read)
+ }
+}
--
2.30.2
next prev parent reply other threads:[~2021-06-07 15:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-07 15:35 [pve-devel] [PATCH v2 0/9] Improve live-restore speed and replace AsyncIndexReader Stefan Reiter
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup 1/9] tools/BroadcastFuture: add testcase for better understanding Stefan Reiter
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup 2/9] tools: add AsyncLruCache as a wrapper around sync LruCache Stefan Reiter
2021-06-07 15:35 ` Stefan Reiter [this message]
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup 4/9] backup: add AsyncRead/Seek to CachedChunkReader Stefan Reiter
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup 5/9] replace AsyncIndexReader with SeekableCachedChunkReader Stefan Reiter
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup 6/9] backup: remove AsyncIndexReader Stefan Reiter
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup 7/9] tools/lru_cache: make minimum capacity 1 Stefan Reiter
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup-qemu 8/9] add shared_cache module Stefan Reiter
2021-06-07 15:35 ` [pve-devel] [PATCH v2 proxmox-backup-qemu 9/9] access: use CachedChunkReader Stefan Reiter
2021-06-08 7:58 ` [pve-devel] applied: [PATCH v2 0/9] Improve live-restore speed and replace AsyncIndexReader Wolfgang Bumiller
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