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    SubjectRe: [PATCH v5 2/2] tmpfs: Support 64-bit inums per-sb
    Hi Hugh,

    Sorry this response took so long, I had some non-work issues that took a lot of
    time last week.

    Hugh Dickins writes:
    >On Fri, 10 Jan 2020, Chris Down wrote:
    >> Hugh Dickins writes:
    >> > 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.
    >>
    >> Based on Mikael's comment above about Steam binaries, and the lack of
    >> likelihood that they can be rebuilt, I'm inclined to still keep inode{64,32},
    >> but make legacy behaviour require explicit opt-in. That is:
    >>
    >> - Default it to inode64
    >> - Remove the Kconfig option
    >> - Only print it as an option if tmpfs was explicitly mounted with inode32
    >>
    >> The reason I suggest keeping this is that I'm mildly concerned that the kind
    >> of users who might be impacted by this change due to 32-bit _FILE_OFFSET_BITS
    >> -- like the not-too-uncommon case that Mikael brings up -- seem unlikely to
    >> be the kind of people that would find it in an rc.
    >
    >Okay. None of us are thrilled with it, but I agree that
    >Mikael's observation should override our developer's preference.
    >
    >So the "inode64" option will be accepted but redundant on mounting,
    >but exists for use as a remount option after mounting or remounting
    >with "inode32": allowing the admin to switch temporarily to mask off
    >the high ino bits with "inode32" when needing to run a limited binary.
    >
    >Documentation and commit message to alert Andrew and Linus and distros
    >that we are risking some breakage with this, but supplying the antidote
    >(not breakage of any distros themselves, no doubt they're all good;
    >but breakage of what some users might run on them).

    Sounds good.

    >>
    >> Other than that, the first patch could be similar to how it is now,
    >> incorporating Hugh's improvements to the first patch to put everything under
    >> the same stat_lock in shmem_reserve_inode.
    >
    >So, I persuaded Amir to the other aspects my version, but did not
    >persuade you? Well, I can live with that (or if not, can send mods
    >on top of yours): but please read again why I was uncomfortable with
    >yours, to check that you still prefer it (I agree that your patch is
    >simpler, and none of my discomfort decisive).

    Hmm, which bit were you thinking of? The lack of batching, shmem_encode_fh(),
    or the fact that nr_inodes can now be 0 on non-internal mounts?

    For batching, I'm neutral. I'm happy to use the approach from your patch and
    integrate it (and credit you, of course).

    For shmem_encode_fh, I'm not totally sure I understand the concern, if that's
    what you mean.

    For nr_inodes, I agree that intentional or unintentional, we should at least
    handle this case for now and can adjust later if the behaviour changes.

    Thanks again,

    Chris

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