[pbs-devel] [PATCH v5 proxmox-backup 6/8] datastore: use custom GC atime cutoff if set

[Christian Ebner <c.ebner@proxmox.com>]

Use the user configured atime cutoff over the default 24h 5m
margin if explicitly set, otherwise fallback to the default.

Move the minimum atime calculation based on the atime cutoff to the
sweep_unused_chunks() callside and pass in the calculated values, as
to have the logic in the same place.

Add log outputs shownig which cutoff and minimum access time is used
by the garbage collection.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 4:
- make gc-atime-cutoff independent from gc-atime-safety-check.
- Refactor cutoff calculation and log it together with the minimum
  atime.
- Conditionally also log in case of oldest writer is outside of range.

 pbs-datastore/src/chunk_store.rs | 10 +---------
 pbs-datastore/src/datastore.rs   | 28 ++++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/pbs-datastore/src/chunk_store.rs b/pbs-datastore/src/chunk_store.rs
index a8c826353..c0e7ded3f 100644
--- a/pbs-datastore/src/chunk_store.rs
+++ b/pbs-datastore/src/chunk_store.rs
@@ -367,7 +367,7 @@ impl ChunkStore {
     pub fn sweep_unused_chunks(
         &self,
         oldest_writer: i64,
-        phase1_start_time: i64,
+        min_atime: i64,
         status: &mut GarbageCollectionStatus,
         worker: &dyn WorkerTaskContext,
     ) -> Result<(), Error> {
@@ -377,14 +377,6 @@ impl ChunkStore {
         use nix::sys::stat::fstatat;
         use nix::unistd::{unlinkat, UnlinkatFlags};
 
-        let mut min_atime = phase1_start_time - 3600 * 24; // at least 24h (see mount option relatime)
-
-        if oldest_writer < min_atime {
-            min_atime = oldest_writer;
-        }
-
-        min_atime -= 300; // add 5 mins gap for safety
-
         let mut last_percentage = 0;
         let mut chunk_count = 0;
 
diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index 5558bb1ac..4af6432ce 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -4,6 +4,7 @@ use std::os::unix::ffi::OsStrExt;
 use std::os::unix::io::AsRawFd;
 use std::path::{Path, PathBuf};
 use std::sync::{Arc, LazyLock, Mutex};
+use std::time::Duration;
 
 use anyhow::{bail, format_err, Error};
 use nix::unistd::{unlinkat, UnlinkatFlags};
@@ -17,6 +18,7 @@ use proxmox_sys::fs::{file_read_optional_string, replace_file, CreateOptions};
 use proxmox_sys::fs::{lock_dir_noblock, DirLockGuard};
 use proxmox_sys::linux::procfs::MountInfo;
 use proxmox_sys::process_locker::ProcessLockSharedGuard;
+use proxmox_time::TimeSpan;
 use proxmox_worker_task::WorkerTaskContext;
 
 use pbs_api_types::{
@@ -1174,6 +1176,7 @@ impl DataStore {
                 DatastoreTuning::API_SCHEMA
                     .parse_property_string(gc_store_config.tuning.as_deref().unwrap_or(""))?,
             )?;
+
             if tuning.gc_atime_safety_check.unwrap_or(true) {
                 self.inner
                     .chunk_store
@@ -1181,7 +1184,28 @@ impl DataStore {
                     .map_err(|err| format_err!("atime safety check failed - {err:#}"))?;
                 info!("Access time safety check successful, proceeding with GC.");
             } else {
-                info!("Filesystem atime safety check disabled by datastore tuning options.");
+                info!("Access time safety check disabled by datastore tuning options.");
+            };
+
+            // Fallback to default 24h 5m if not set
+            let cutoff = tuning
+                .gc_atime_cutoff
+                .map(|cutoff| cutoff * 60)
+                .unwrap_or(3600 * 24 + 300);
+
+            let mut min_atime = phase1_start_time - cutoff as i64;
+            info!(
+                "Using access time cutoff {}, minimum access time is {}",
+                TimeSpan::from(Duration::from_secs(cutoff as u64)),
+                proxmox_time::epoch_to_rfc3339_utc(min_atime)?,
+            );
+            if oldest_writer < min_atime {
+                min_atime = oldest_writer - 300; // account for 5 min safety gap
+                info!(
+                    "Oldest backup writer started at {}, extending minimum access time to {}",
+                    TimeSpan::from(Duration::from_secs(oldest_writer as u64)),
+                    proxmox_time::epoch_to_rfc3339_utc(min_atime)?,
+                );
             }
 
             info!("Start GC phase1 (mark used chunks)");
@@ -1191,7 +1215,7 @@ impl DataStore {
             info!("Start GC phase2 (sweep unused chunks)");
             self.inner.chunk_store.sweep_unused_chunks(
                 oldest_writer,
-                phase1_start_time,
+                min_atime,
                 &mut gc_status,
                 worker,
             )?;
-- 
2.39.5



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