From: Rik van Riel <riel@surriel.com>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc: Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@techsingularity.net>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] bounds: Support non-power-of-two CONFIG_NR_CPUS
Date: Tue, 10 Oct 2023 11:19:34 -0400 [thread overview]
Message-ID: <4d29a5c75d1120d095f27e8e453da9b00c1336d5.camel@surriel.com> (raw)
In-Reply-To: <20231010145549.1244748-1-willy@infradead.org>
On Tue, 2023-10-10 at 15:55 +0100, Matthew Wilcox (Oracle) wrote:
> 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.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Fixes: 90572890d202 ("mm: numa: Change page last {nid,pid} into
> {cpu,pid}")
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Rik van Riel <riel@surriel.com>
Reviewed-by: Rik van Riel <riel@surriel.com>
--
All Rights Reversed.
next prev parent reply other threads:[~2023-10-10 15:19 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-10 14:55 Matthew Wilcox (Oracle)
2023-10-10 15:19 ` Rik van Riel [this message]
2023-10-10 15:31 ` Mel Gorman
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