linux-kernel - Re: [PATCH v2 2/7] radix-tree: Use local

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Message-ID: <20200525132606.GB3066456@gmail.com>
Date:   Mon, 25 May 2020 15:26:06 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 2/7] radix-tree: Use local_lock for protection


* Matthew Wilcox <willy@...radead.org> wrote:

> On Mon, May 25, 2020 at 08:29:54AM +0200, Ingo Molnar wrote:
> > > +void radix_tree_preload_end(void)
> > > +{
> > > +	local_unlock(&radix_tree_preloads.lock);
> > > +}
> > > +EXPORT_SYMBOL(radix_tree_preload_end);
> > 
> > Since upstream we are still mapping the local_lock primitives to
> > preempt_disable()/preempt_enable(), I believe these uninlining changes should not be done
> > in this patch, i.e. idr_preload_end() and radix_tree_preload_end() should stay inline.
> 
> But radix_tree_preloads is static, and I wouldn't be terribly happy to
> see that exported to modules.

Well, it seems a bit silly to make radix_tree_preload_end() a 
standalone function, on most distro kernels that don't have 
CONFIG_PREEMPT=y, preempt_enable() is a NOP:

 0000000000002bf0 <radix_tree_preload_end>:
     2bf0:       c3                      retq   

I.e. we'd be introducing a separate function call for no good reason.

Thanks,

	Ingo