linux-kernel - Re: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb

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Date:   Tue, 7 Jan 2020 12:12:00 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Dave Chinner <david@...morbit.com>,
        Chris Down <chris@...isdown.name>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Jeff Layton <jlayton@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, kernel-team@...com
Subject: Re: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb

On Tue, Jan 7, 2020 at 10:36 AM Hugh Dickins <hughd@...gle.com> wrote:
>
> On Tue, 7 Jan 2020, Amir Goldstein wrote:
> > On Tue, Jan 7, 2020 at 2:40 AM Dave Chinner <david@...morbit.com> wrote:
> > > On Tue, Jan 07, 2020 at 12:16:43AM +0000, Chris Down wrote:
> > > > Dave Chinner writes:
> > > > > It took 15 years for us to be able to essentially deprecate
> > > > > inode32 (inode64 is the default behaviour), and we were very happy
> > > > > to get that albatross off our necks.  In reality, almost everything
> > > > > out there in the world handles 64 bit inodes correctly
> > > > > including 32 bit machines and 32bit binaries on 64 bit machines.
> > > > > And, IMNSHO, there no excuse these days for 32 bit binaries that
> > > > > don't using the *64() syscall variants directly and hence support
> > > > > 64 bit inodes correctlyi out of the box on all platforms.
>
> Interesting take on it.  I'd all along imagined we would have to resort
> to a mount option for safety, but Dave is right that I was too focused on
> avoiding tmpfs regressions, without properly realizing that people were
> very unlikely to have written such tools for tmpfs in particular, but
> written them for all filesystems, and already encountered and fixed
> such EOVERFLOWs for other filesystems.
>
> Hmm, though how readily does XFS actually reach the high inos on
> ordinary users' systems?
>

Define 'ordinary'
I my calculations are correct, with default mkfs.xfs any inode allocated
from logical offset > 2TB on a volume has high ino bits set.
Besides, a deployment with more than 4G inodes shouldn't be hard to find.

Thanks,
Amir.