Re: [PATCH v2] KEYS: key_garbage_collector(): process in chunks

[sashiko-bot@kernel.org]

> key_garbage_collector() has a design that is not resistant enough for
> workqueue lockups. The duration scales up relative to the number of items
> in the serial tree, which causes a reoccuring theme of being guilty of
> causing workqueue lockups.
> 
> Resolve the problem by processing in chunks:
> 
> 1. Declare a static variable key_gc_work, which owns the garbage collection
>    in-flight state, and key_schedule_gc_work() for re-scheduling the work.
> 2. Define KEY_GC_CHUNK_SIZE, set to 1024 keys, as the bound for the number
>    of items scanned and destroyed.
> 3. Define KEY_GC_DESTROYING to mark resume to destruction without repeating
>    the RCU grace period. Drain the graveyard before advancing key-type
>    reaping.
> 4. Define KEY_GC_REAP_REQUESTED for preserving full-pass requests across
> [ ... ]
> - aarch64: chunk max: 235 ms, total time increase: 6%
> 
> Tests were performed using a laptop with AMD 4650U (Zen 2 uarch) CPU.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Sashiko has reviewed this patch and found no issues.

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