linux-kernel - Re: [PATCH 2/3] lockdep: clarify size for LOCKDEP_*

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Message-ID: <218314e9-7c7c-490c-bb2e-9611243cade3@redhat.com>
Date: Mon, 5 Aug 2024 21:36:43 -0400
From: Waiman Long <longman@...hat.com>
To: Carlos Llamas <cmllamas@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
 Peter Zijlstra <peterz@...radead.org>, Boqun Feng <boqun.feng@...il.com>,
 Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH 2/3] lockdep: clarify size for LOCKDEP_*_BITS configs

On 8/5/24 21:01, Carlos Llamas wrote:
> The LOCKDEP_*_BITS configs control the size of internal structures used
> by lockdep. The size is calculated as a power of two of the configured
> value (e.g. 16 => 64KB). Update these descriptions to more accurately
> reflect this, as "Bitsize" can be misleading.
>
> Suggested-by: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
> ---
>   lib/Kconfig.debug | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index baaaedfde0cb..e0614a415348 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1505,7 +1505,7 @@ config LOCKDEP_SMALL
>   	bool
>   
>   config LOCKDEP_BITS
> -	int "Bitsize for MAX_LOCKDEP_ENTRIES"
> +	int "Size for MAX_LOCKDEP_ENTRIES (as Nth power of 2)"
>   	depends on LOCKDEP && !LOCKDEP_SMALL
>   	range 10 24
>   	default 15
> @@ -1513,7 +1513,7 @@ config LOCKDEP_BITS
>   	  Try increasing this value if you hit "BUG: MAX_LOCKDEP_ENTRIES too low!" message.
>   
>   config LOCKDEP_CHAINS_BITS
> -	int "Bitsize for MAX_LOCKDEP_CHAINS"
> +	int "Size for MAX_LOCKDEP_CHAINS (as Nth power of 2)"
>   	depends on LOCKDEP && !LOCKDEP_SMALL
>   	range 10 21
>   	default 16
> @@ -1521,7 +1521,7 @@ config LOCKDEP_CHAINS_BITS
>   	  Try increasing this value if you hit "BUG: MAX_LOCKDEP_CHAINS too low!" message.
>   
>   config LOCKDEP_STACK_TRACE_BITS
> -	int "Bitsize for MAX_STACK_TRACE_ENTRIES"
> +	int "Size for MAX_STACK_TRACE_ENTRIES (as Nth power of 2)"
>   	depends on LOCKDEP && !LOCKDEP_SMALL
>   	range 10 26
>   	default 19
> @@ -1529,7 +1529,7 @@ config LOCKDEP_STACK_TRACE_BITS
>   	  Try increasing this value if you hit "BUG: MAX_STACK_TRACE_ENTRIES too low!" message.
>   
>   config LOCKDEP_STACK_TRACE_HASH_BITS
> -	int "Bitsize for STACK_TRACE_HASH_SIZE"
> +	int "Size for STACK_TRACE_HASH_SIZE (as Nth power of 2)"
>   	depends on LOCKDEP && !LOCKDEP_SMALL
>   	range 10 26
>   	default 14
> @@ -1537,7 +1537,7 @@ config LOCKDEP_STACK_TRACE_HASH_BITS
>   	  Try increasing this value if you need large STACK_TRACE_HASH_SIZE.
>   
>   config LOCKDEP_CIRCULAR_QUEUE_BITS
> -	int "Bitsize for elements in circular_queue struct"
> +	int "Size for elements in circular_queue struct (as Nth power of 2)"
>   	depends on LOCKDEP
>   	range 10 26
>   	default 12

Many kernel developers understand that BITS refers to a size of 2^n. 
Besides LOCKDEP, there are also many instances of such use in other 
kconfig entries. It can be a bit odd to explicitly state that just for 
LOCKDEP.

Cheers,
Longman