[PATCH proxmox 1/3] pbs-api-types: add gc chunk metadata prefetch tuning option

[Enrico Plantulli <plantulli@gmail.com>]

Garbage collection phase 1 reaches each chunk by building its path from
the digest, so it never iterates the chunk directories. On file systems
that prefetch inode metadata while iterating a directory, that leaves a
large win unused: a single readdir pass over .chunks/ brings in the
metadata in bulk, while phase 1 on its own faults it in one chunk at a
time, in an order uncorrelated with the on-disk layout.

Add an opt-in tuning option so that garbage collection can do that pass
before phase 1. It defaults to false because the pass costs time on file
systems that do not prefetch inodes on readdir, and on datastores whose
metadata already fits in the cache.

Signed-off-by: Enrico Plantulli <plantulli@gmail.com>
---
 pbs-api-types/src/datastore.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/pbs-api-types/src/datastore.rs b/pbs-api-types/src/datastore.rs
index 93ccaf0..76ecc5b 100644
--- a/pbs-api-types/src/datastore.rs
+++ b/pbs-api-types/src/datastore.rs
@@ -278,6 +278,14 @@ pub const GC_CACHE_CAPACITY_SCHEMA: Schema =
             schema: GC_CACHE_CAPACITY_SCHEMA,
             optional: true,
         },
+        "gc-chunk-metadata-prefetch": {
+            description:
+                "Iterate the chunk directories once before garbage collection phase 1, so the \
+                file system can fault in chunk metadata in bulk instead of one chunk at a time",
+            optional: true,
+            default: false,
+            type: bool,
+        },
         "default-verification-workers": {
             schema: VERIFY_JOB_VERIFY_THREADS_SCHEMA,
             optional: true,
@@ -304,6 +312,8 @@ pub struct DatastoreTuning {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub gc_cache_capacity: Option<usize>,
     #[serde(skip_serializing_if = "Option::is_none")]
+    pub gc_chunk_metadata_prefetch: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub default_verification_workers: Option<usize>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub default_verification_readers: Option<usize>,

base-commit: e3e3ff11b9b92fe1ace89b84c1e15c150e2db660
-- 
2.47.3