linux-ext4 - Re: "beyond 2038" warnings from loopback mount is noisy

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Date:   Tue, 3 Sep 2019 14:31:06 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Qian Cai <cai@....pw>, Jeff Layton <jlayton@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: "beyond 2038" warnings from loopback mount is noisy

On Tue, Sep 3, 2019 at 2:18 PM Theodore Y. Ts'o <tytso@....edu> wrote:
>
> On Tue, Sep 03, 2019 at 09:18:44AM -0700, Deepa Dinamani wrote:
> >
> > This prints a warning for each inode that doesn't extend limits beyond
> > 2038. It is rate limited by the ext4_warning_inode().
> > Looks like your filesystem has inodes that cannot be extended.
> > We could use a different rate limit or ignore this corner case. Do the
> > maintainers have a preference?
>
> We need to drop this commit (ext4: Initialize timestamps limits), or
> at least the portion which adds the call to the EXT4_INODE_SET_XTIME
> macro in ext4.h.

As Arnd said, I think this can be fixed by warning only when the inode
size is not uniformly 128 bytes in ext4.h. Is this an acceptable
solution or we want to drop this warning altogether?

Arnd, should I be sending a pull request again with the fix? Or, we
drop the ext4 patch and I can send it to the maintainers directly?

> I know of a truly vast number of servers in production all over the
> world which are using 128 byte inodes, and spamming the inodes at the
> maximum rate limit is a really bad idea.  This includes at some major
> cloud data centers where the life of individual servers in their data
> centers is well understood (they're not going to last until 2038) and
> nothing stored on the local Linux file systems are long-lived ---
> that's all stored in the cluster file systems.  The choice of 128 byte
> inode was deliberately chosen to maximize storage TCO, and so spamming
> a warning at high rates is going to be extremely unfriendly.
>
> In cases where the inode size is such that there is no chance at all
> to support timestamps beyond 2038, a single warning at mount time, or
> maybe a warning at mkfs time might be acceptable.  But there's no
> point printing a warning time each time we set a timestamp on such a
> file system.  It's not going to change, and past a certain point, we
> need to trust that people who are using 128 byte inodes did so knowing
> what the tradeoffs might be.  After all, it is *not* the default.

We have a single mount time warning already in place here. I did not
realize some people actually chose to use 128 byte inodes on purpose.

-Deepa