linux-kernel - Re: [PATCH v2 0/6] locking/lockdep: Reuse zapped chain

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Date:   Mon, 6 Jan 2020 10:54:24 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>
Cc:     linux-kernel@...r.kernel.org, Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCH v2 0/6] locking/lockdep: Reuse zapped chain_hlocks entries

On 12/16/19 10:15 AM, Waiman Long wrote:
>  v2:
>   - Revamp the chain_hlocks reuse patch to store the freed chain_hlocks
>     information in the chain_hlocks entries themselves avoiding the
>     need of a separate set of tracking structures. This, however,
>     requires a minimum allocation size of at least 2. Thanks to PeterZ
>     for his review and inspiring this change.
>   - Remove the leakage counter as it is no longer applicable.
>   - Add patch 6 to make the output of /proc/lockdep_chains more readable.
>
> It was found that when running a workload that kept on adding lock
> classes and then zapping them repetitively, the system will eventually
> run out of chain_hlocks[] entries even though there were still plenty
> of other lockdep data buffers available.
>
>   [ 4318.443670] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
>   [ 4318.444809] turning off the locking correctness validator.
>
> In order to fix this problem, we have to make chain_hlocks[] entries
> reusable just like other lockdep arrays. Besides that, the patchset
> also adds some zapped class and chain_hlocks counters to be tracked by
> /proc/lockdep_stats. It also fixes leakage in the irq context counters
> and makes the output of /proc/lockdep_chains more readable.
>
> Waiman Long (6):
>   locking/lockdep: Track number of zapped classes
>   locking/lockdep: Throw away all lock chains with zapped class
>   locking/lockdep: Track number of zapped lock chains
>   locking/lockdep: Reuse freed chain_hlocks entries
>   locking/lockdep: Decrement irq context counters when removing lock
>     chain
>   locking/lockdep: Display irq_context names in /proc/lockdep_chains
>
>  kernel/locking/lockdep.c           | 307 +++++++++++++++++++++++------
>  kernel/locking/lockdep_internals.h |  14 +-
>  kernel/locking/lockdep_proc.c      |  26 ++-
>  3 files changed, 282 insertions(+), 65 deletions(-)
>
Ping! Any comments or suggestion for further improvement?

Cheers,
Longman