[pbs-devel] [PATCH v4 proxmox-backup 6/8] datastore: conditionally use custom GC atime cutoff if set

[Christian Ebner]

Use the user configured atime cutoff over the default 24h 5m
margin if explicitly set, but only if the atime safety check is
enabled and succeeded. If the atime safety check is not enabled,
fallback to use the current 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.

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
changes since version 3:
- move min_atime calculation to the gc atime cutoff logic, pass the
  min_atime to sweep_unused_chunks()

 pbs-datastore/src/chunk_store.rs | 10 +---------
 pbs-datastore/src/datastore.rs   | 30 ++++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/pbs-datastore/src/chunk_store.rs b/pbs-datastore/src/chunk_store.rs
index e482330b3..0b211a44c 100644
--- a/pbs-datastore/src/chunk_store.rs
+++ b/pbs-datastore/src/chunk_store.rs
@@ -364,7 +364,7 @@ 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> {
@@ -374,14 +374,6 @@ 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 b62ddc172..16767832e 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -1174,12 +1174,38 @@ 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) {
+            let gc_atime_safety_check = tuning.gc_atime_safety_check.unwrap_or(true);
+            if gc_atime_safety_check {
                 self.inner.chunk_store.check_fs_atime_updates(true)?;
             } else {
                 info!("Filesystem atime safety check disabled by datastore tuning options.");
+            };
+
+            let mut min_atime = tuning
+                .gc_atime_cutoff
+                .and_then(|cutoff| {
+                    if gc_atime_safety_check {
+                        info!("Using GC atime cutoff {cutoff}m.");
+                        // Account for the 5 min default offset subtracted below
+                        Some(phase1_start_time + 300 - cutoff as i64 * 60)
+                    } else {
+                        warn!(
+                            "Ignoring GC atime cutoff of {cutoff}m since atime check is disabled."
+                        );
+                        None
+                    }
+                })
+                .unwrap_or_else(|| {
+                    info!("Using default GC atime cutoff of 24h 5m");
+                    phase1_start_time - 3600 * 24
+                });
+
+            if oldest_writer < min_atime {
+                min_atime = oldest_writer;
             }
 
+            min_atime -= 300; // add 5 mins gap for safety
+
             info!("Start GC phase1 (mark used chunks)");
 
             self.mark_used_chunks(&mut gc_status, worker)?;
@@ -1187,7 +1213,7 @@ 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