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| author | Matthew Wilcox (Oracle) <willy@infradead.org> | 2023-10-10 15:55:49 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-02-22 15:38:51 -0800 |
| commit | f2d5dcb48f7ba9e3ff249d58fc1fa963d374e66a (patch) | |
| tree | 744ff726fea20e15c0f719c65d10a2420001843e /kernel/bounds.c | |
| parent | b401b621758e46812da61fa58a67c3fd8d91de0d (diff) | |
| download | lwn-f2d5dcb48f7ba9e3ff249d58fc1fa963d374e66a.tar.gz lwn-f2d5dcb48f7ba9e3ff249d58fc1fa963d374e66a.zip | |
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@infradead.org>
Fixes: 90572890d202 ("mm: numa: Change page last {nid,pid} into {cpu,pid}")
Reviewed-by: Rik van Riel <riel@surriel.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'kernel/bounds.c')
| -rw-r--r-- | kernel/bounds.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/bounds.c b/kernel/bounds.c index b529182e8b04..c5a9fcd2d622 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 |