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Subject: Re: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb
From:   Jeff Layton <jlayton@kernel.org>
To:     Hugh Dickins <hughd@google.com>, Chris Mason <clm@fb.com>
Cc:     Dave Chinner <david@fromorbit.com>,
        Amir Goldstein <amir73il@gmail.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>,
        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>
Date:   Wed, 08 Jan 2020 19:43:52 -0500
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On Wed, 2020-01-08 at 03:24 -0800, Hugh Dickins wrote:
> 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.

This approach seems like the best course to me.

FWIW, at the time we capped this at 32-bits (2007), 64-bit machines were
really just becoming widely available, and it was quite common to run
32-bit, non-LFS apps on a 64-bit kernel. Users were hitting spurious
EOVERFLOW errors all over the place so this seemed like the best way to
address it.

The world has changed a lot since then though, and one would hope that
almost everything these days is compiled with FILE_OFFSET_BITS=64.

Fingers crossed!
-- 
Jeff Layton <jlayton@kernel.org>