linux-ext4 - Re: [PATCH 0/7] jbd2: Bit spinlock conversions

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Message-ID: <alpine.DEB.2.21.1908022245510.4029@nanos.tec.linutronix.de>
Date:   Fri, 2 Aug 2019 22:46:57 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jan Kara <jack@...e.cz>
cc:     Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Julia Cartwright <julia@...com>
Subject: Re: [PATCH 0/7] jbd2: Bit spinlock conversions

Jan,

On Fri, 2 Aug 2019, Jan Kara wrote:

> This series is derived from Thomas' series to get rid of bit spinlocks in
> buffer head code. These patches convert BH_State bit spinlock to an ordinary
> spinlock inside struct journal_head and somewhat reduce the critical section
> under BH_JournalHead bit spinlock so that it is fine for RT. 

Thanks a lot for cleaning this up!

> Motivation from original Thomas' series:
> 
> Bit spinlocks are problematic if PREEMPT_RT is enabled. They disable
> preemption, which is undesired for latency reasons and breaks when regular
> spinlocks are taken within the bit_spinlock locked region because regular
> spinlocks are converted to 'sleeping spinlocks' on RT.
> 
> Bit spinlocks are also not covered by lock debugging, e.g. lockdep. With
> the spinlock substitution in place, they can be exposed via a new config
> switch: CONFIG_DEBUG_BIT_SPINLOCKS.
> 
> WRT patch routing: Since these are non-trivial changes to JBD2 and independent
> of the rest of the series from Thomas, I think it would be safest to route
> them through ext4 tree where they get most testing. Thoughts?

Yes, there is no dependency, so feel free to route it through ext4.

Thanks,

	tglx