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From: Christian Ebner <c.ebner@proxmox.com>
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Subject: [pbs-devel] [PATCH v3 proxmox-backup 6/6] fix #5331: garbage
collection: avoid multiple chunk atime updates
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To reduce the number of atimes updates, keep track of the recently
marked chunks in phase 1 of garbage to avoid multiple atime updates
via expensive utimensat() calls.
Recently touched chunks are tracked by storing the chunk digests in
an LRU cache of fixed capacity. By inserting a digest, the chunk will
be the most recently touched one and if already present in the cache
before insert, the atime update can be skipped.
Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=5331
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 2:
- Switch to LRU cache instead of keeping track of chunks from previous
snapshot of the same group.
pbs-datastore/src/datastore.rs | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)
diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index c4123f2b7..1f1c3b396 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -7,6 +7,7 @@ use std::sync::{Arc, LazyLock, Mutex};
use anyhow::{bail, format_err, Context, Error};
use nix::unistd::{unlinkat, UnlinkatFlags};
+use pbs_tools::lru_cache::LruCache;
use tracing::{info, warn};
use proxmox_human_byte::HumanByte;
@@ -1081,6 +1082,7 @@ impl DataStore {
&self,
index: Box<dyn IndexFile>,
file_name: &Path, // only used for error reporting
+ recently_touched_chunks: &mut LruCache<[u8; 32], ()>,
status: &mut GarbageCollectionStatus,
worker: &dyn WorkerTaskContext,
) -> Result<(), Error> {
@@ -1091,6 +1093,12 @@ impl DataStore {
worker.check_abort()?;
worker.fail_on_shutdown()?;
let digest = index.index_digest(pos).unwrap();
+
+ // Avoid multiple expensive atime updates by utimensat
+ if recently_touched_chunks.insert(*digest, ()) {
+ continue;
+ }
+
if !self.inner.chunk_store.cond_touch_chunk(digest, false)? {
let hex = hex::encode(digest);
warn!(
@@ -1131,6 +1139,8 @@ impl DataStore {
let mut unprocessed_image_list = self.list_images()?;
let image_count = unprocessed_image_list.len();
+ // Allow up to 32 MiB, as only storing the 32 digest as key
+ let mut recently_touched_chunks = LruCache::new(1024 * 1024);
let mut processed_images = 0;
let mut last_percentage: usize = 0;
@@ -1157,7 +1167,13 @@ impl DataStore {
Some(index) => index,
None => continue,
};
- self.index_mark_used_chunks(index, &path, status, worker)?;
+ self.index_mark_used_chunks(
+ index,
+ &path,
+ &mut recently_touched_chunks,
+ status,
+ worker,
+ )?;
unprocessed_image_list.remove(&path);
@@ -1184,7 +1200,13 @@ impl DataStore {
Some(index) => index,
None => continue,
};
- self.index_mark_used_chunks(index, &path, status, worker)?;
+ self.index_mark_used_chunks(
+ index,
+ &path,
+ &mut recently_touched_chunks,
+ status,
+ worker,
+ )?;
warn!(
"Marked chunks for unexpected index file at '{}'",
path.to_string_lossy()
--
2.39.5
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