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L2ARC: Write budget fairness for metadata monopolization

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Under heavy metadata load, metadata passes can monopolize the write
budget every cycle while data passes get nothing written. Track
consecutive monopolized cycles per device in l2ad_meta_cycles. After
l2arc_meta_cycles (default 2) consecutive cycles where metadata fills
the write budget, skip metadata for one cycle to let data run.  Reset
the counter when nothing is written.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #18289
This commit is contained in:
Ameer Hamza
2026-03-05 19:17:03 +05:00
committed by Brian Behlendorf
parent 62ca8f721b
commit b27a87f399
4 changed files with 50 additions and 0 deletions
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include/sys/arc_impl.h
+6
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@@ -469,6 +469,12 @@ typedef struct l2arc_dev {
boolean_t l2ad_thread_exit; /* signal thread exit */
kmutex_t l2ad_feed_thr_lock; /* thread sleep/wake */
kcondvar_t l2ad_feed_cv; /* thread wakeup cv */
/*
* Consecutive cycles where metadata filled write budget
* while data passes got nothing written. Used to detect
* monopolization and skip metadata to give data a chance.
*/
uint64_t l2ad_meta_cycles;
} l2arc_dev_t;
/*