linux-kernel - Re: [PATCH] fs/buffer: Make BH_Uptodate_Lock bit_spin_lock a regular spinlock

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Message-ID: <20191115173634.GC23689@mit.edu>
Date:   Fri, 15 Nov 2019 12:36:34 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     Sebastian Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Matthew Wilcox <willy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.com>, Mark Fasheh <mark@...heh.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Christoph Hellwig <hch@...radead.org>,
        Joel Becker <jlbec@...lplan.org>
Subject: Re: [PATCH] fs/buffer: Make BH_Uptodate_Lock bit_spin_lock a regular
 spinlock_t

On Fri, Nov 15, 2019 at 03:56:38PM +0100, Jan Kara wrote:
> With some effort, we could even shrink struct buffer_head from 104 bytes
> (on x86_64) to 96 bytes but I don't think that effort is worth it (I'd find
> it better use of time to actually work on getting rid of buffer heads
> completely).

Is that really realistic?  All aside from the very large number of
file systems which use buffer_heads that would have to be reworked,
the concept of buffer heads is pretty fundamental to how jbd2 is
architected.

					- Ted