linux-kernel - Re: [PATCH] eventfs: Have inodes have unique inode numbers

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Message-ID: <CAHk-=wiF0ATuuxJhwgm707izS=5q4xBUSh+06U2VwFEJj0FNRw@mail.gmail.com>
Date: Fri, 26 Jan 2024 14:48:45 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Steven Rostedt <rostedt@...dmis.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	Linux Trace Devel <linux-trace-devel@...r.kernel.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Christian Brauner <brauner@...nel.org>, Ajay Kaher <ajay.kaher@...adcom.com>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] eventfs: Have inodes have unique inode numbers

On Fri, 26 Jan 2024 at 14:34, Matthew Wilcox <willy@...radead.org> wrote:
>
> On Fri, Jan 26, 2024 at 05:14:12PM -0500, Mathieu Desnoyers wrote:
> > I would suggest this straightforward solution to this:
> >
> > a) define a EVENTFS_MAX_INODES (e.g. 4096 * 8),
> >
> > b) keep track of inode allocation in a bitmap (within a single page),
> >
> > c) disallow allocating more than "EVENTFS_MAX_INODES" in eventfs.
>
> ... reinventing the IDA?

Guysm, this is a random number that is *so* interesting that I
seriously think we shouldn't have it at all.

End result: nobody should care. Even the general VFS layer doesn't care.

It literally avoids inode number zero, not because it would be a bad
inode number, but simply because of some random historical oddity.

In fact, I don't think we even have a reason for it. We have a commit
2adc376c5519 ("vfs: avoid creation of inode number 0 in get_next_ino")
and that one calls out glibc for not deleting them. That makes no
sense to me, but whatever.

But note how the generic function does *not* try to make them unique,
for example. They are just "unique enough".

The generic function *does* care about being scalable in an SMP
environment. To a disturbing degree. Oh well.

                Linus