linux-kernel - Re: [PATCH 00/13] VFS: Filesystem information [ver #19]

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Message-ID: <CAJfpeguxACC68bMhS-mNm4m6ytrKgs1--jbF5X3tBiPf_iG1jg@mail.gmail.com>
Date:   Wed, 1 Apr 2020 14:35:54 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     David Howells <dhowells@...hat.com>
Cc:     Ian Kent <raven@...maw.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux NFS list <linux-nfs@...r.kernel.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Linux API <linux-api@...r.kernel.org>,
        linux-ext4@...r.kernel.org,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Christian Brauner <christian@...uner.io>,
        Jann Horn <jannh@...gle.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Karel Zak <kzak@...hat.com>, Jeff Layton <jlayton@...hat.com>,
        linux-fsdevel@...r.kernel.org,
        LSM <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/13] VFS: Filesystem information [ver #19]

On Wed, Apr 1, 2020 at 10:37 AM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Wed, Apr 1, 2020 at 10:27 AM David Howells <dhowells@...hat.com> wrote:
> >
> > Miklos Szeredi <miklos@...redi.hu> wrote:
> >
> > > According to dhowell's measurements processing 100k mounts would take
> > > about a few seconds of system time (that's the time spent by the
> > > kernel to retrieve the data,
> >
> > But the inefficiency of mountfs - at least as currently implemented - scales
> > up with the number of individual values you want to retrieve, both in terms of
> > memory usage and time taken.
>
> I've taken that into account when guesstimating a "few seconds per
> 100k entries".  My guess is that there's probably an order of
> magnitude difference between the performance of a fs based interface
> and a binary syscall based interface.  That could be reduced somewhat
> with a readfile(2) type API.

And to show that I'm not completely off base, attached a patch that
adds a limited readfile(2) syscall and uses it in the p2 method.

Results are promising:

./test-fsinfo-perf /tmp/a 30000
--- make mounts ---
--- test fsinfo by path ---
sum(mnt_id) = 930000
--- test fsinfo by mnt_id ---
sum(mnt_id) = 930000
--- test /proc/fdinfo ---
sum(mnt_id) = 930000
--- test mountfs ---
sum(mnt_id) = 930000
For   30000 mounts, f=    146400us f2=    136766us p=   1406569us p2=
  221669us; p=9.6*f p=10.3*f2 p=6.3*p2
--- umount ---

This is about a 2 fold increase in speed compared to open + read + close.

Is someone still worried about performance, or can we move on to more
interesting parts of the design?

Thanks,
Miklos

View attachment "fsmount-readfile.patch" of type "text/x-patch" (6326 bytes)