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

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Message-ID: <20190810081834.GB30426@infradead.org>
Date:   Sat, 10 Aug 2019 01:18:34 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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

On Thu, Aug 08, 2019 at 09:54:03AM +0200, Thomas Gleixner wrote:
> > I know.  But the problem here is that normally PG_locked is used together 
> > with wait_on_page_bit_*, but this one instances uses the bit spinlock
> > helpers.  This is the equivalent of calling spin_lock on a struct mutex
> > rather than having a mutex_lock_spin helper for this case.
> 
> Yes, I know :(

But this means we should exclude slub from the bit_spin_lock removal.
It really should use it's own version of it anyhow insted of pretending
that the page lock is a bit spinlock.

> 
> > Does SLUB work on -rt at all?
> 
> It's the only allocator we support with a few tweaks :)

What do you do about this particular piece of code there?