Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley
        Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United
        Kingdom.
        Registered in England and Wales under Company Registration No. 3798903
From:   David Howells <dhowells@redhat.com>
In-Reply-To: <CAJfpegt=cQ159kEH9zCYVHV7R_08jwMxF0jKrSUV5E=uBg4Lzw@mail.gmail.com>
References: <CAJfpegt=cQ159kEH9zCYVHV7R_08jwMxF0jKrSUV5E=uBg4Lzw@mail.gmail.com> <1842689.1596468469@warthog.procyon.org.uk> <1845353.1596469795@warthog.procyon.org.uk> <CAJfpegunY3fuxh486x9ysKtXbhTE0745ZCVHcaqs9Gww9RV2CQ@mail.gmail.com> <ac1f5e3406abc0af4cd08d818fe920a202a67586.camel@themaw.net> <CAJfpegu8omNZ613tLgUY7ukLV131tt7owR+JJ346Kombt79N0A@mail.gmail.com> <CAJfpegtNP8rQSS4Z14Ja4x-TOnejdhDRTsmmDD-Cccy2pkfVVw@mail.gmail.com> <20200811135419.GA1263716@miu.piliscsaba.redhat.com> <CAHk-=wjzLmMRf=QG-n+1HnxWCx4KTQn9+OhVvUSJ=ZCQd6Y1WA@mail.gmail.com> <52483.1597190733@warthog.procyon.org.uk>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     dhowells@redhat.com,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Karel Zak <kzak@redhat.com>,
        Jeff Layton <jlayton@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        Christian Brauner <christian@brauner.io>,
        Lennart Poettering <lennart@poettering.net>,
        Linux API <linux-api@vger.kernel.org>,
        Ian Kent <raven@themaw.net>,
        LSM <linux-security-module@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <98801.1597220949.1@warthog.procyon.org.uk>
Date:   Wed, 12 Aug 2020 09:29:09 +0100
Message-ID: <98802.1597220949@warthog.procyon.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Miklos Szeredi <miklos@szeredi.hu> 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?

David