linux-kernel - Re: [PATCH v3 3/3] lockdep: document MAX_LOCKDEP_CHAIN

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Message-ID: <b0cae30d-03d9-40cd-aba6-88ce9bd4d906@redhat.com>
Date: Thu, 24 Oct 2024 15:01:12 -0400
From: Waiman Long <llong@...hat.com>
To: Carlos Llamas <cmllamas@...gle.com>, Boqun Feng <boqun.feng@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Will Deacon <will@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
 Huang Ying <ying.huang@...el.com>, "J. R. Okajima" <hooanon05g@...il.com>
Subject: Re: [PATCH v3 3/3] lockdep: document MAX_LOCKDEP_CHAIN_HLOCKS
 calculation

On 10/24/24 2:36 PM, Carlos Llamas wrote:
> Define a macro AVG_LOCKDEP_CHAIN_DEPTH to document the magic number '5'
> used in the calculation of MAX_LOCKDEP_CHAIN_HLOCKS. The number
> represents the estimated average depth (number of locks held) of a lock
> chain. The calculation of MAX_LOCKDEP_CHAIN_HLOCKS was first added in
> commit 443cd507ce7f ("lockdep: add lock_class information to lock_chain
> and output it").
>
> Suggested-by: Waiman Long <longman@...hat.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: J. R. Okajima <hooanon05g@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Acked-by: Waiman Long <longman@...hat.com>
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
> ---
> v3: collect tags
> v2: switched the comment for a macro as suggested by Waiman Long.
>
>   kernel/locking/lockdep_internals.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
> index bbe9000260d0..20f9ef58d3d0 100644
> --- a/kernel/locking/lockdep_internals.h
> +++ b/kernel/locking/lockdep_internals.h
> @@ -119,7 +119,8 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
>   
>   #define MAX_LOCKDEP_CHAINS	(1UL << MAX_LOCKDEP_CHAINS_BITS)
>   
> -#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
> +#define AVG_LOCKDEP_CHAIN_DEPTH		5
> +#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS * AVG_LOCKDEP_CHAIN_DEPTH)
>   
>   extern struct lock_chain lock_chains[];
>   
Acked-by: Waiman Long <longman@...hat.com>