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Date:   Wed, 12 Aug 2020 10:37:08 +0200
From:   Miklos Szeredi <>
To:     David Howells <>
Cc:     Linus Torvalds <>,
        linux-fsdevel <>,
        Al Viro <>, Karel Zak <>,
        Jeff Layton <>,
        Miklos Szeredi <>,
        Nicolas Dichtel <>,
        Christian Brauner <>,
        Lennart Poettering <>,
        Linux API <>,
        Ian Kent <>,
        LSM <>,
        Linux Kernel Mailing List <>
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)

On Wed, Aug 12, 2020 at 10:29 AM David Howells <> wrote:
> Miklos Szeredi <> wrote:
> > Worried about performance?  Io-uring will allow you to do all those
> > five syscalls (or many more) with just one I/O submission.
> io_uring isn't going to help here.  We're talking about synchronous reads.
> AIUI, you're adding a couple more syscalls to the list and running stuff in a
> side thread to save the effort of going in and out of the kernel five times.
> But you still have to pay the set up/tear down costs on the fds and do the
> pathwalks.  io_uring doesn't magically make that cost disappear.
> io_uring also requires resources such as a kernel accessible ring buffer to
> make it work.
> You're proposing making everything else more messy just to avoid a dedicated
> syscall.  Could you please set out your reasoning for that?

a) A dedicated syscall with a complex binary API is a non-trivial
maintenance burden.

b) The awarded performance boost is not warranted for the use cases it
is designed for.


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