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Date:   Mon, 18 Nov 2019 10:35:44 +0100
From:   Jan Kara <>
To:     "Theodore Y. Ts'o" <>
Cc:     Jan Kara <>, Sebastian Siewior <>,
        Thomas Gleixner <>,
        Matthew Wilcox <>,
        LKML <>,,,
        Peter Zijlstra <>,
        Ingo Molnar <>,
        Anna-Maria Gleixner <>,
        Steven Rostedt <>,
        Julia Cartwright <>,
        Alexander Viro <>,
        Jan Kara <>, Mark Fasheh <>,
        Joseph Qi <>,
        Christoph Hellwig <>,
        Joel Becker <>
Subject: Re: [PATCH] fs/buffer: Make BH_Uptodate_Lock bit_spin_lock a regular

On Fri 15-11-19 12:36:34, Theodore Y. Ts'o wrote:
> 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.

I think it is reasonably possible to remove buffer_heads from data path
(including direct IO path) of all filesystems. That way memory consumption
of buffer_heads becomes mostly irrelevant and we can have a look how much
from the current bh framework still makes sense...

Jan Kara <>

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