linux-kernel - FAILED: Patch "bounds: support non-power-of-two CONFIG_NR

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Message-ID: <20240327122125.2836828-1-sashal@kernel.org>
Date: Wed, 27 Mar 2024 08:21:25 -0400
From: Sasha Levin <sashal@...nel.org>
To: stable@...r.kernel.org,
	willy@...radead.org
Cc: Rik van Riel <riel@...riel.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@...r.kernel.org>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

>From f2d5dcb48f7ba9e3ff249d58fc1fa963d374e66a Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Date: Tue, 10 Oct 2023 15:55:49 +0100
Subject: [PATCH] bounds: support non-power-of-two CONFIG_NR_CPUS

ilog2() rounds down, so for example when PowerPC 85xx sets CONFIG_NR_CPUS
to 24, we will only allocate 4 bits to store the number of CPUs instead of
5.  Use bits_per() instead, which rounds up.  Found by code inspection.
The effect of this would probably be a misaccounting when doing NUMA
balancing, so to a user, it would only be a performance penalty.  The
effects may be more wide-spread; it's hard to tell.

Link: https://lkml.kernel.org/r/20231010145549.1244748-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Fixes: 90572890d202 ("mm: numa: Change page last {nid,pid} into {cpu,pid}")
Reviewed-by: Rik van Riel <riel@...riel.com>
Acked-by: Mel Gorman <mgorman@...hsingularity.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
 kernel/bounds.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bounds.c b/kernel/bounds.c
index b529182e8b04f..c5a9fcd2d6228 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -19,7 +19,7 @@ int main(void)
 	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
 	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
 #ifdef CONFIG_SMP
-	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
+	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
 #endif
 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
 #ifdef CONFIG_LRU_GEN
-- 
2.43.0