gc: expose per-pdev backlog and pressure metrics - #462
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Add five per-pdev gauges to pdev_gc_metrics for operator visibility into the GC backlog: - pending_gc_bytes reclaimable bytes in PG-owned chunks - eligible_gc_bytes bytes GC would pick up under current policy - eligible_gc_chunk_count count for the above - pending_normal_gc_task_count normal-priority queue depth - pending_gc_chunks_ratio 10-series labeled gauge over (0,10]% .. (90,100]% The bucket metric emits as a single Prometheus family with a 'bucket' label, differentiated by direct m_impl_ptr->register_gauge() calls (the compile-time-name macro cannot express label-differentiated series). Descriptions embed the bucket label so the sisl JSON dump does not collapse the 10 entries to one. Values are refreshed once per gc_scan_interval by scan_chunks_for_gc, using a new private GCManager::get_chunk_gc_snapshot helper that folds the four ExtendedVChunk field reads into a single lookup per chunk; get_chunk_gc_ratio is retained as a thin wrapper for backward compatibility.
| LOGINFOMOD(gcmgr, | ||
| "pdev_id={} already has {}/{} pending normal gc tasks, skipping submission this scan cycle", | ||
| pdev_id, already_pending, max_task_num); | ||
| continue; |
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when reaching here, it means some gc tasks are backloged. it is valuable for us to report eligible_gc_bytes/eligible_gc_chunk_count/pending_gc_chunks_ratio , etc. to metrics now to show us the gc pressure.
if we just continue and skip publish_scan_snapshot, we can not get those information timely.
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Add five per-pdev gauges to pdev_gc_metrics for operator visibility into the GC backlog:
The bucket metric emits as a single Prometheus family with a 'bucket' label, differentiated by direct m_impl_ptr->register_gauge() calls (the compile-time-name macro cannot express label-differentiated series). Descriptions embed the bucket label so the sisl JSON dump does not collapse the 10 entries to one.
Values are refreshed once per gc_scan_interval by scan_chunks_for_gc, using a new private GCManager::get_chunk_gc_snapshot helper that folds the four ExtendedVChunk field reads into a single lookup per chunk; get_chunk_gc_ratio is retained as a thin wrapper for backward compatibility.