[pbs-devel] [PATCH v3 proxmox-backup 7/9] 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.

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
changes since version 2:
- Adapt datastore tuning option names
- Fallback to default on relatime behaviour

 pbs-datastore/src/chunk_store.rs |  9 ++++++++-
 pbs-datastore/src/datastore.rs   | 28 +++++++++++++++++++++++++---
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/pbs-datastore/src/chunk_store.rs b/pbs-datastore/src/chunk_store.rs
index e529dcc9c..f591412a2 100644
--- a/pbs-datastore/src/chunk_store.rs
+++ b/pbs-datastore/src/chunk_store.rs
@@ -371,6 +371,7 @@ impl ChunkStore {
         &self,
         oldest_writer: i64,
         phase1_start_time: i64,
+        atime_cutoff: Option<usize>,
         status: &mut GarbageCollectionStatus,
         worker: &dyn WorkerTaskContext,
     ) -> Result<(), Error> {
@@ -380,7 +381,13 @@ 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)
+        let mut min_atime = if let Some(atime_cutoff) = atime_cutoff {
+            // account for the default 5 min safety gap subtracted below
+            phase1_start_time + 300 - atime_cutoff as i64 * 60
+        } else {
+            // at least 24h (see mount option relatime)
+            phase1_start_time - 3600 * 24
+        };
 
         if oldest_writer < min_atime {
             min_atime = oldest_writer;
diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index ef932b47b..4f07cfc60 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -1174,11 +1174,32 @@ 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.atime_safety_check()?;
-                info!("Filesystem atime safety check successful.");
+            let gc_atime_safety_check = tuning.gc_atime_safety_check.unwrap_or(true);
+            let atime_updated = if gc_atime_safety_check {
+                if self.inner.chunk_store.atime_safety_check()? {
+                    info!("Filesystem atime safety check successful.");
+                    true
+                } else {
+                    info!("Filesystem atime safety check successful with relatime behaviour.");
+                    false
+                }
             } else {
                 info!("Filesystem atime safety check disabled by datastore tuning options.");
+                false
+            };
+            let mut atime_cutoff = None;
+            if let Some(cutoff) = tuning.gc_atime_cutoff {
+                if atime_updated {
+                    info!("Using GC atime cutoff {cutoff}m.");
+                    atime_cutoff = Some(cutoff);
+                } else {
+                    warn!(
+                        "Ignoring GC atime cutoff of {cutoff}m, because atime check is \
+                        disabled or relatime behaviour detected."
+                    );
+                }
+            } else {
+                info!("Using default GC atime cutoff of 24h 5m");
             }
 
             info!("Start GC phase1 (mark used chunks)");
@@ -1189,6 +1210,7 @@ impl DataStore {
             self.inner.chunk_store.sweep_unused_chunks(
                 oldest_writer,
                 phase1_start_time,
+                atime_cutoff,
                 &mut gc_status,
                 worker,
             )?;
-- 
2.39.5