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[backup.rs] Subject: Re: [pve-devel] [pbs-devel] [PATCH proxmox-backup 3/9] backup: add CachedChunkReader utilizing AsyncLruCache X-BeenThere: pve-devel@lists.proxmox.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Proxmox VE development discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 04 Jun 2021 12:22:41 -0000 On Wed, Jun 02, 2021 at 04:38:27PM +0200, Stefan Reiter wrote: > Provides a fast cache read implementation with full async and > concurrency support. > > Signed-off-by: Stefan Reiter > --- > > 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. > > src/backup.rs | 3 ++ > src/backup/cached_chunk_reader.rs | 87 +++++++++++++++++++++++++++++++ > 2 files changed, 90 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..fd5a049f > --- /dev/null > +++ b/src/backup/cached_chunk_reader.rs > @@ -0,0 +1,87 @@ > +//! 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 { > + reader: Arc, > +} > + > +impl AsyncCacher<[u8; 32], Arc>> > + for AsyncChunkCacher > +{ > + fn fetch( > + &self, > + key: [u8; 32], > + ) -> Box>>, 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))) > + }) > + } > +} > + > +/// Represents an AsyncLruCache used for storing data chunks. > +pub type ChunkCache = Arc>>>; Given that you now use this type in an external crate but still have to *instantiate* it via `Arc::new(AsyncLruCache::new(...))` I wonder if this should just be a struct prividing a `new`, `clone` and `Deref`? > + > +/// 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 { > + cache: ChunkCache, > + cacher: AsyncChunkCacher, > + index: I, > +} > + > +impl CachedChunkReader { > + /// 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: ChunkCache) -> 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 { > + 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) { > + let info = self.index.chunk_info(chunk.0).unwrap(); > + > + // will never be None, see AsyncChunkCacher Why comment on this unwrap but not on the one above? ;-) > + 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