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    SubjectRe: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb
    On Tue, Jan 07, 2020 at 12:12:00PM +0200, Amir Goldstein wrote:
    > On Tue, Jan 7, 2020 at 10:36 AM Hugh Dickins <hughd@google.com> wrote:
    > >
    > > On Tue, 7 Jan 2020, Amir Goldstein wrote:
    > > > On Tue, Jan 7, 2020 at 2:40 AM Dave Chinner <david@fromorbit.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.

    You don't need to allocate 4 billion inodes to get >32bit inodes in
    XFS - the inode number is an encoding of the physical location of
    the inode in the filesystem. Hence we just have to allocate the
    inode at a disk address higher than 2TB into the device and we
    overflow 32bits.

    e.g. make a sparse fs image file of 10TB, mount it, create 50
    subdirs, then start creating zero length files spread across the 50
    separate subdirectories. You should see >32bit inode numbers almost
    immediately. (i.e. as soon as we allocate inodes in AG 2 or higher)

    IOWs, there are *lots* of 64bit inode numbers out there on XFS
    filesystems....

    Cheers,

    Dave.
    --
    Dave Chinner
    david@fromorbit.com

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