linux-kernel - [PATCH v2 3/3] lockdep: document MAX_LOCKDEP_CHAIN

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Message-ID: <20240807143922.919604-4-cmllamas@google.com>
Date: Wed,  7 Aug 2024 14:39:19 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: 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, 
	Andrew Morton <akpm@...ux-foundation.org>, Carlos Llamas <cmllamas@...gle.com>, 
	Waiman Long <longman@...hat.com>, Huang Ying <ying.huang@...el.com>, 
	"J. R. Okajima" <hooanon05g@...il.com>, Boqun Feng <boqun.feng@...il.com>
Subject: [PATCH v2 3/3] lockdep: document MAX_LOCKDEP_CHAIN_HLOCKS calculation

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>
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
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[];
 
-- 
2.46.0.rc2.264.g509ed76dc8-goog