linux-kernel - Re: [patch V2 0/7] fs: Substitute bit-spinlocks for PREEMPT

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Message-ID: <alpine.DEB.2.21.1908021107090.2285@nanos.tec.linutronix.de>
Date:   Fri, 2 Aug 2019 11:07:53 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Christoph Hellwig <hch@...radead.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>, Jan Kara <jack@...e.cz>,
        Theodore Tso <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        Jan Kara <jack@...e.com>, Mark Fasheh <mark@...heh.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Joel Becker <jlbec@...lplan.org>
Subject: Re: [patch V2 0/7] fs: Substitute bit-spinlocks for PREEMPT_RT and
 debugging

Christoph,

On Fri, 2 Aug 2019, Christoph Hellwig wrote:

> did you look into killing bіt spinlocks as a public API instead?

Last time I did, there was resistance :)

But I'm happy to try again.

> The main users seems to be buffer heads, which are so bloated that
> an extra spinlock doesn't really matter anyway.
>
> The list_bl and rhashtable uses kinda make sense to be, but they are
> pretty nicely abstracted away anyway.  The remaining users look
> pretty questionable to start with.

What about the page lock?

  mm/slub.c:      bit_spin_lock(PG_locked, &page->flags);

Thanks,

	tglx