linux-kernel - [for-linus][PATCH 10/15] ftrace: Simplify the hash calculation

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Date:   Tue, 06 Oct 2020 10:34:56 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [for-linus][PATCH 10/15] ftrace: Simplify the hash calculation

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

No need to add a check to subtract the number of bits if bits is zero after
fls(). Just divide the size by two before calling it. This does give the
same answer for size of 0 and 1, but that's fine.

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/ftrace.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 5633d37d8806..c51a91aea1fd 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1368,11 +1368,10 @@ static struct ftrace_hash *dup_hash(struct ftrace_hash *src, int size)
 	int i;
 
 	/*
-	 * Make the hash size about 1/2 the # found
+	 * Use around half the size (max bit of it), but
+	 * a minimum of 2 is fine (as size of 0 or 1 both give 1 for bits).
 	 */
-	bits = fls(size);
-	if (bits)
-		bits--;
+	bits = fls(size / 2);
 
 	/* Don't allocate too much */
 	if (bits > FTRACE_HASH_MAX_BITS)
-- 
2.28.0