linux-kernel - Re: [patch 5/5] sched: Move mmdrop to RCU on RT

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Message-ID: <87ilyj8rbu.ffs@tglx>
Date:   Wed, 29 Sep 2021 15:05:41 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [patch 5/5] sched: Move mmdrop to RCU on RT

On Wed, Sep 29 2021 at 14:02, Peter Zijlstra wrote:
> On Tue, Sep 28, 2021 at 02:24:32PM +0200, Thomas Gleixner wrote:
>> +#ifdef CONFIG_PREEMPT_RT
>> +/*
>> + * RCU callback for delayed mm drop. Not strictly RCU, but call_rcu() is
>> + * by far the least expensive way to do that.
>> + */
>> +void __mmdrop_delayed(struct rcu_head *rhp)
>> +{
>> +	struct mm_struct *mm = container_of(rhp, struct mm_struct, delayed_drop);
>> +
>> +	__mmdrop(mm);
>> +}
>> +#endif
>
> Would you mind terribly if I fold this into mm.h as a static inline ?
>
> The only risk that carries is that if mmdrop_sched() is called from
> multiple translation units (it is not) we get multiple instances of this
> function, but possibly even !LTO linkers can fix that for us.

No preference here.