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

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Message-ID: <ZrI3mFLUwDyEMRIB@google.com>
Date: Tue, 6 Aug 2024 14:47:52 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Waiman Long <longman@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 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 Mon, Aug 05, 2024 at 09:36:43PM -0400, Waiman Long wrote:
> 
> 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

Right, and similar to BITS there is SHIFT, which is also a common way to
specify the 2^n values. I'd point out though, that it is also common to
clarify the "power of two" explicitly. To name a few examples that are
doing so: SECURITY_SELINUX_SIDTAB_HASH_BITS, NODES_SHIFT, CMA_ALIGNMENT,
IP_VS_SH_TAB_BITS, LOG_BUF_SHIFT but there is more.

Perhaps this is because the audience for these configs is not always a
kernel developer?

Anyway, this is pretty much a trivial patch to address Andrew's comment
below. But let me know if you think I should drop it, it seems to me it
can be helpful.

  [...]
  btw, the help text "Bitsize for MAX_LOCKDEP_CHAINS" is odd.  What's a
  bitsize?  Maybe "bit shift count for..." or such.

Thanks,
--
Carlos Llamas