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Date:   Wed, 8 Jan 2020 03:24:42 -0800 (PST)
From:   Hugh Dickins <hughd@google.com>
To:     Chris Mason <clm@fb.com>
cc:     Dave Chinner <david@fromorbit.com>,
        Amir Goldstein <amir73il@gmail.com>,
        Hugh Dickins <hughd@google.com>,
        Chris Down <chris@chrisdown.name>,
        Linux MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Matthew Wilcox <willy@infradead.org>,
        Jeff Layton <jlayton@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tejun Heo <tj@kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb
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On Tue, 7 Jan 2020, Chris Mason wrote:
> On 7 Jan 2020, at 16:07, Dave Chinner wrote:
> 
> > IOWs, there are *lots* of 64bit inode numbers out there on XFS
> > filesystems....
> 
> It's less likely in btrfs but +1 to all of Dave's comments.  I'm happy 
> to run a scan on machines in the fleet and see how many have 64 bit 
> inodes (either buttery or x-y), but it's going to be a lot.

Dave, Amir, Chris, many thanks for the info you've filled in -
and absolutely no need to run any scan on your fleet for this,
I think we can be confident that even if fb had some 15-year-old tool
in use on its fleet of 2GB-file filesystems, it would not be the one
to insist on a kernel revert of 64-bit tmpfs inos.

The picture looks clear now: while ChrisD does need to hold on to his
config option and inode32/inode64 mount option patch, it is much better
left out of the kernel until (very unlikely) proved necessary.

Thanks,
Hugh