From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux Trace Devel <linux-trace-devel@vger.kernel.org>,
Christian Brauner <brauner@kernel.org>,
Ajay Kaher <ajay.kaher@broadcom.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] eventfs: Have inodes have unique inode numbers
Date: Sun, 28 Jan 2024 21:32:49 -0500 [thread overview]
Message-ID: <20240128213249.605a7ade@rorschach.local.home> (raw)
In-Reply-To: <CAHk-=wjKagcAh5rHuNPMqp9hH18APjF4jW7LQ06pNQwZ1Qp0Eg@mail.gmail.com>
On Sun, 28 Jan 2024 17:42:30 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Sun, 28 Jan 2024 at 17:00, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > mkdir dummy
> > cd dummy
> > echo "Hello" > hello
> > ( sleep 10; cat ) < hello &
> > rm hello
> > cd ..
> > rmdir dummy
>
> Note that it's worth repeating that simple_recursive_removal()
> wouldn't change any of the above. It only unhashes things and makes
> them *look* gone, doing things like clearing i_nlink etc.
I know, but I already cover the above case. And that case is not what
simple_recursive_removal() is covering.
I'm worried about what can be opened after a deletion. Not what has
already been opened. The simple_recrusive_removal() is the way to clear
the dcache on those files and directories that are being removed so
that no new references can happen on them.
So, I removed the simple_recursive_removal() from the code to see what
happened. Interesting, the opposite occurred.
# cd /sys/kernel/tracing
# echo 'p:sched schedule' > kprobe_events
# ls events/kprobes
enable filter sched
# ls events/kprobes/sched
enable filter format hist hist_debug id inject trigger
# cat events/kprobes/sched/enable
0
# echo 'p:timer read_current_timer' >> kprobe_events
# ls events/kprobes
enable filter sched timer
Now delete just one kprobe (keeping the kprobes directory around)
# echo '-:sched schedule' >> kprobe_events
# ls events/kprobes/
enable filter timer
Now recreate that kprobe
# echo 'p:sched schedule' >> kprobe_events
# ls events/kprobes
enable filter sched timer
# ls events/kprobes/sched/
ls: reading directory 'events/kprobes/sched/': Invalid argument
I have no access to the directory that was deleted and recreated.
>
> But those VFS data structures would still exist, and the files that
> had them open would still continue to be open.
>
> So if you thought that simple_recursive_removal() would make the above
> kind of thing not able to happen, and that eventfs wouldn't have to
> deal with dentries that point to event_inodes that are dead, you were
> always wrong.
No but I want to shrink the dentries after the directory is removed.
Perhaps something else is the error here.
>
> simple_recursive_removal() is mostly just lipstick on a pig. It does
> cause the cached dentries that have no active use be removed earlier,
> so it has that "memory pressure" kind of effect, but it has no real
> fundamental semantic effect.
I was using it to "flush" the cache on that directory. Nothing more.
>
> Of course, for a filesystem where the dentry tree *is* the underlying
> data (ie the 'tmpfs' kind, but also things like debugfs or ipathfs,
> for example), then things are different.
Note, tracefs was built on debugfs. Only the "events" directory is
"different". The rest of /sys/kernel/tracing behaves exactly like
debugfs.
>
> There the dentries are the primary thing, and not just a cache in
> front of the backing store.
>
> But you didn't want that, and those days are long gone as far as
> tracefs is concerned.
Well, as long as eventfs is ;-)
-- Steve
next prev parent reply other threads:[~2024-01-29 2:32 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-26 20:02 [PATCH] eventfs: Have inodes have unique inode numbers Steven Rostedt
2024-01-26 20:25 ` Linus Torvalds
2024-01-26 21:26 ` Steven Rostedt
2024-01-26 21:31 ` Linus Torvalds
2024-01-26 21:43 ` Steven Rostedt
2024-01-26 21:36 ` Linus Torvalds
2024-01-26 21:42 ` Steven Rostedt
2024-01-26 21:49 ` Linus Torvalds
2024-01-26 22:08 ` Steven Rostedt
2024-01-26 22:26 ` Linus Torvalds
2024-01-27 14:47 ` Steven Rostedt
2024-01-28 14:42 ` Steven Rostedt
2024-01-26 22:14 ` Mathieu Desnoyers
2024-01-26 22:29 ` Linus Torvalds
2024-01-26 22:41 ` Mathieu Desnoyers
2024-01-26 22:49 ` Linus Torvalds
2024-01-29 16:00 ` Mathieu Desnoyers
2024-01-29 18:58 ` Linus Torvalds
2024-01-26 22:34 ` Matthew Wilcox
2024-01-26 22:40 ` Mathieu Desnoyers
2024-01-26 22:48 ` Linus Torvalds
2024-01-26 23:04 ` Matthew Wilcox
2024-01-26 23:11 ` Linus Torvalds
2024-01-26 23:17 ` Linus Torvalds
2024-01-27 9:36 ` Andreas Schwab
2024-01-27 21:47 ` Linus Torvalds
2024-01-28 20:15 ` Steven Rostedt
2024-01-28 20:53 ` Linus Torvalds
2024-01-28 21:08 ` Linus Torvalds
2024-01-28 22:01 ` Steven Rostedt
2024-01-28 22:17 ` Linus Torvalds
2024-01-28 22:26 ` Steven Rostedt
2024-01-28 21:11 ` Steven Rostedt
2024-01-28 21:19 ` Steven Rostedt
2024-01-28 21:43 ` Linus Torvalds
2024-01-28 22:07 ` Linus Torvalds
2024-01-28 22:17 ` Steven Rostedt
2024-01-28 22:25 ` Linus Torvalds
2024-01-28 22:51 ` Steven Rostedt
2024-01-28 23:24 ` Linus Torvalds
2024-01-28 23:59 ` Steven Rostedt
2024-01-29 0:21 ` Steven Rostedt
2024-01-29 1:00 ` Linus Torvalds
2024-01-29 1:42 ` Linus Torvalds
2024-01-29 2:32 ` Steven Rostedt [this message]
2024-01-29 3:40 ` Steven Rostedt
2024-01-29 4:01 ` Linus Torvalds
2024-01-29 2:09 ` Steven Rostedt
2024-01-29 6:44 ` Amir Goldstein
2024-01-29 9:32 ` Steven Rostedt
2024-01-27 15:26 ` David Laight
2024-01-27 20:01 ` Linus Torvalds
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