linux-kernel - Re: [PATCH 01/10] mm: pagecache add lock

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Message-ID: <20180523171204.GA20772@kmo-pixel>
Date:   Wed, 23 May 2018 13:12:04 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <dchinner@...hat.com>, darrick.wong@...cle.com,
        tytso@....edu, linux-btrfs@...r.kernel.org, clm@...com,
        jbacik@...com, viro@...iv.linux.org.uk, peterz@...radead.org
Subject: Re: [PATCH 01/10] mm: pagecache add lock

On Wed, May 23, 2018 at 08:22:39AM -0700, Christoph Hellwig wrote:
> On Sun, May 20, 2018 at 06:45:24PM -0400, Kent Overstreet wrote:
> > > 
> > > Honestly I think this probably should be in the core.  But IFF we move
> > > it to the core the existing users of per-fs locks need to be moved
> > > over first.  E.g. XFS as the very first one, and at least ext4 and f2fs
> > > that copied the approach, and probably more if you audit deep enough.
> > 
> > I'm not going to go and redo locking in XFS and ext4 as a prerequisite to
> > merging bcachefs. Sorry, but that's a bit crazy.
> 
> It isn't crazy at all.  In general we expect people to do their fair
> share of core work to get their pet feature in.  How much is acceptable
> is a difficult question and not black and white.
> 
> But if you want to grow a critical core structure you better take a stab
> at converting existing users.  Without that the tradeoff of growing
> that core structure is simply not given.
> 
> Or to put it in words for this exact feature:  unless your new field
> is also used by mainstream file systems it is not going to be added.

Christoph, I'm really not someone you can accuse of avoiding my share of core
work and refactoring and you know it.

When are you going to get around to converting existing users of fs/direct-io.c
to iomap so it can be deleted? The kernel is carrying around two dio
implementations right now thanks to you. Not a good situation, is it?