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From: Fabian =?iso-8859-1?q?Gr=FCnbichler?= <f.gruenbichler@proxmox.com>
To: Proxmox Backup Server development discussion <pbs-devel@lists.proxmox.com>
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Subject: Re: [pbs-devel] [PATCH v2 proxmox-backup 4/4] fix #5331: garbage
collection: avoid multiple chunk atime updates
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On March 10, 2025 12:16 pm, Christian Ebner wrote:
> Reduce the number of atime updates on the same chunk by logically
> iterating over image index files, following the incremental backup
> logic. By inserting paths for encountered images during
> `list_images` using the GroupedImageList structure, the iteration
> happens now for the same image filenames in the same image namespace
> and group in a order based on the snapshot timestamp. For each image,
> keep track of the encountered chunk digests, and remember these as
> seen for the next snapshot. Chunks which have been encountered in the
> previous image index, but are not present anymore are removed from
> the list after each image, in order to reduce memory footprint.
>
> Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=5331
> Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
technically this could be split into two parts - one for the iterating
change, one for the performance optimization? with the latter part maybe
being combined with patch#3 and the order switched around? ;)
> ---
> changes since version 1:
> - Use pre-existing datastore iterator helpers, following the logic other
> datastore operations take.
> - Chunks are now remembered for all archives per snapshot, not just a
> single archive per snapshot as previously, this mimics more closely
> the backup behaviour.
>
> pbs-datastore/src/datastore.rs | 117 +++++++++++++++++++++++----------
> 1 file changed, 84 insertions(+), 33 deletions(-)
>
> diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
> index fdbb33a98..a80343d9b 100644
> --- a/pbs-datastore/src/datastore.rs
> +++ b/pbs-datastore/src/datastore.rs
> @@ -25,7 +25,7 @@ use pbs_api_types::{
> MaintenanceMode, MaintenanceType, Operation, UPID,
> };
>
> -use crate::backup_info::{BackupDir, BackupGroup};
> +use crate::backup_info::{BackupDir, BackupGroup, BackupInfo};
> use crate::chunk_store::ChunkStore;
> use crate::dynamic_index::{DynamicIndexReader, DynamicIndexWriter};
> use crate::fixed_index::{FixedIndexReader, FixedIndexWriter};
> @@ -970,10 +970,10 @@ impl DataStore {
> ListGroups::new(Arc::clone(self), ns)?.collect()
> }
>
> - fn list_images(&self) -> Result<Vec<PathBuf>, Error> {
> + fn list_images(&self) -> Result<HashSet<PathBuf>, Error> {
> let base = self.base_path();
>
> - let mut list = vec![];
> + let mut list = HashSet::new();
>
> use walkdir::WalkDir;
>
> @@ -1021,7 +1021,7 @@ impl DataStore {
> if archive_type == ArchiveType::FixedIndex
> || archive_type == ArchiveType::DynamicIndex
> {
> - list.push(path);
> + list.insert(path);
> }
> }
> }
> @@ -1071,6 +1071,7 @@ impl DataStore {
> &self,
> index: Box<dyn IndexFile>,
> file_name: &Path, // only used for error reporting
> + touched_chunks: &mut TouchedChunks,
> status: &mut GarbageCollectionStatus,
> worker: &dyn WorkerTaskContext,
> ) -> Result<(), Error> {
> @@ -1081,6 +1082,12 @@ impl DataStore {
> worker.check_abort()?;
> worker.fail_on_shutdown()?;
> let digest = index.index_digest(pos).unwrap();
> +
> + // Avoid multiple expensive atime updates by utimensat
> + if touched_chunks.insert(*digest) {
> + continue;
> + }
> +
> if !self.inner.chunk_store.cond_touch_chunk(digest, false)? {
> let hex = hex::encode(digest);
> warn!(
> @@ -1107,43 +1114,87 @@ impl DataStore {
> status: &mut GarbageCollectionStatus,
> worker: &dyn WorkerTaskContext,
> ) -> Result<(), Error> {
> - let image_list = self.list_images()?;
> - let image_count = image_list.len();
> -
> + // Iterate twice over the datastore to fetch images, even if this comes with an additional
> + // runtime cost:
> + // - First iteration to find all index files, no matter if they are in a location expected
> + // by the datastore's hierarchy
> + // - Iterate using the datastore's helpers, so the namespaces, groups and snapshots are
> + // looked up given the expected hierarchy and iterator logic
> + //
> + // By this it is assured that all index files are used, even if they would not have been
> + // seen by the regular logic and the user is informed by the garbage collection run about
> + // the detected index files not following the iterators logic.
> +
> + let mut unprocessed_image_list = self.list_images()?;
> + let image_count = unprocessed_image_list.len();
> +
> + // Optimize for avoiding updates of chunks atime in same group for consecutive
> + // snapshots multiple times.
> + let mut touched_chunks = TouchedChunks::new();
> + let mut processed_images = 0;
> let mut last_percentage: usize = 0;
>
> - let mut strange_paths_count: u64 = 0;
> -
> - for (i, img) in image_list.into_iter().enumerate() {
> - worker.check_abort()?;
> - worker.fail_on_shutdown()?;
> -
> - if let Some(backup_dir_path) = img.parent() {
> - let backup_dir_path = backup_dir_path.strip_prefix(self.base_path())?;
> - if let Some(backup_dir_str) = backup_dir_path.to_str() {
> - if pbs_api_types::parse_ns_and_snapshot(backup_dir_str).is_err() {
> - strange_paths_count += 1;
> + let arc_self = Arc::new(self.clone());
> + for namespace in arc_self
> + .recursive_iter_backup_ns(BackupNamespace::root())
> + .context("creating namespace iterator failed")?
> + {
> + let namespace = namespace.context("iterating namespaces failed")?;
> + for group in arc_self.iter_backup_groups(namespace)? {
> + let group = group.context("iterating backup groups failed")?;
> + let mut snapshots = group.list_backups().context("listing snapshots failed")?;
> + // Sort by snapshot timestamp to iterate over consecutive snapshots for each image.
> + BackupInfo::sort_list(&mut snapshots, true);
> + for snapshot in snapshots {
> + for file in snapshot.files {
> + worker.check_abort()?;
> + worker.fail_on_shutdown()?;
> +
> + let mut path = snapshot.backup_dir.full_path();
> + path.push(file);
> +
> + let index = match self.open_index_reader(&path)? {
> + Some(index) => index,
> + None => continue,
> + };
> + self.index_mark_used_chunks(
> + index,
> + &path,
> + &mut touched_chunks,
> + status,
> + worker,
> + )?;
> +
> + unprocessed_image_list.remove(&path);
> +
> + let percentage = (processed_images + 1) * 100 / image_count;
> + if percentage > last_percentage {
> + info!(
> + "marked {percentage}% ({} of {image_count} index files)",
> + processed_images + 1,
> + );
> + last_percentage = percentage;
> + }
> + processed_images += 1;
> }
> + touched_chunks.reset();
> }
> }
> -
> - if let Some(index) = self.open_index_reader(&img)? {
> - self.index_mark_used_chunks(index, &img, status, worker)?;
> - }
> -
> - let percentage = (i + 1) * 100 / image_count;
> - if percentage > last_percentage {
> - info!(
> - "marked {percentage}% ({} of {image_count} index files)",
> - i + 1,
> - );
> - last_percentage = percentage;
> - }
> }
>
> + let strange_paths_count = unprocessed_image_list.len();
> if strange_paths_count > 0 {
> - info!(
> - "found (and marked) {strange_paths_count} index files outside of expected directory scheme"
> + warn!("found {strange_paths_count} index files outside of expected directory scheme");
> + }
> + for path in unprocessed_image_list {
> + let index = match self.open_index_reader(&path)? {
> + Some(index) => index,
> + None => continue,
> + };
> + self.index_mark_used_chunks(index, &path, &mut touched_chunks, status, worker)?;
> + warn!(
> + "Marked chunks for unexpected index file at '{}'",
> + path.to_string_lossy()
> );
> }
>
> --
> 2.39.5
>
>
>
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