linux-kernel - Re: [PATCH 2/6] futex: Implement FUTEX2

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Message-ID: <i4ljhfndmqrdg5zevd4gf2chmzesfieflxvfj2io2qfhfj4vb7@nicvpjmcdtyu>
Date: Fri, 25 Oct 2024 11:30:26 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Peter Zijlstra <peterz@...radead.org>
Cc: tglx@...utronix.de, linux-kernel@...r.kernel.org, mingo@...hat.com, 
	dvhart@...radead.org, andrealmeid@...lia.com, 
	Andrew Morton <akpm@...ux-foundation.org>, urezki@...il.com, hch@...radead.org, lstoakes@...il.com, 
	Arnd Bergmann <arnd@...db.de>, linux-api@...r.kernel.org, linux-mm@...ck.org, 
	linux-arch@...r.kernel.org, malteskarupke@....de, cl@...ux.com, llong@...hat.com
Subject: Re: [PATCH 2/6] futex: Implement FUTEX2_NUMA

On Fri, 25 Oct 2024, Peter Zijlstra wrote:\n

> static int __init futex_init(void)
> {
>-	unsigned int futex_shift;
>-	unsigned long i;
>+	unsigned int order, n;
>+	unsigned long size, i;
>
> #ifdef CONFIG_BASE_SMALL
> 	futex_hashsize = 16;
> #else
>-	futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
>+	futex_hashsize = 256 * num_possible_cpus();
>+	futex_hashsize /= num_possible_nodes();
>+	futex_hashsize = roundup_pow_of_two(futex_hashsize);
> #endif
>+	futex_hashshift = ilog2(futex_hashsize);
>+	size = sizeof(struct futex_hash_bucket) * futex_hashsize;
>+	order = get_order(size);
>+
>+	for_each_node(n) {

Probably want to skip nodes that don't have CPUs, those will never
have the remote for .node value.