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Date: Mon, 28 Oct 2024 11:24:27 +0100
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org,
	=?utf-8?B?QW5kcsOp?= Almeida <andrealmeid@igalia.com>,
	Darren Hart <dvhart@infradead.org>,
	Davidlohr Bueso <dave@stgolabs.net>, Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Waiman Long <longman@redhat.com>
Subject: Re: [RFC PATCH 3/3] futex: Use the task local hashmap.
Message-ID: <20241028102427.rhVmBDLD@linutronix.de>
References: <20241026224306.982896-1-bigeasy@linutronix.de>
 <20241026224306.982896-4-bigeasy@linutronix.de>
 <20241028102253.GN9767@noisy.programming.kicks-ass.net>
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In-Reply-To: <20241028102253.GN9767@noisy.programming.kicks-ass.net>

On 2024-10-28 11:22:53 [+0100], Peter Zijlstra wrote:
> >  struct futex_hash_bucket *futex_hash(union futex_key *key)
> >  {
> > +	struct futex_hash_table *fht;
> >  	u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
> >  			  key->both.offset);
> >  
> > +	fht = current->futex_hash_table;
> > +	if (fht && (key->both.offset & (FUT_OFF_INODE | FUT_OFF_MMSHARED)) == 0)
> > +		return &fht->queues[hash & (fht->slots - 1)];
> 
> Perhaps add a helper like:
> 
> static inline bool futex_key_is_private(struct futex_key *key)
> {
> 	/*
> 	 * Relies on get_futex_key() to set either bit for shared
> 	 * futexes -- see comment with union futex_key.
> 	 */
> 	return !(key->both.offset & (FUT_OFF_INODE | FUT_OFF_MMSHARED));
> }

Oki.

Sebastian