The patch titled
Subject: bounds: support non-power-of-two CONFIG_NR_CPUS
has been added to the -mm mm-nonmm-unstable branch. Its filename is
bounds-support-non-power-of-two-config_nr_cpus.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/bounds-support-non-power-of-two-config_nr_cpus.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: bounds: support non-power-of-two CONFIG_NR_CPUS
Date: Tue, 10 Oct 2023 15:55:49 +0100
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@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Fixes: 90572890d202 ("mm: numa: Change page last {nid,pid} into {cpu,pid}")
Reviewed-by: Rik van Riel <riel@xxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/bounds.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/bounds.c~bounds-support-non-power-of-two-config_nr_cpus
+++ a/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
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
bounds-support-non-power-of-two-config_nr_cpus.patch
