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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Tue, 3 Mar 2020 10:48:01 +0100
Message-ID: <CAJfpegtemv64mpmTRT6ViHmsWq4nNE4KQvuHkNCYozRU7dQd8Q@mail.gmail.com>
Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17]
To:     David Howells <dhowells@redhat.com>
Cc:     Ian Kent <raven@themaw.net>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        Steven Whitehouse <swhiteho@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Jann Horn <jannh@google.com>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Linux API <linux-api@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Tue, Mar 3, 2020 at 10:26 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Tue, Mar 3, 2020 at 10:13 AM David Howells <dhowells@redhat.com> wrote:
> >
> > Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > > I'm doing a patch.   Let's see how it fares in the face of all these
> > > preconceptions.
> >
> > Don't forget the efficiency criterion.  One reason for going with fsinfo(2) is
> > that scanning /proc/mounts when there are a lot of mounts in the system is
> > slow (not to mention the global lock that is held during the read).

BTW, I do feel that there's room for improvement in userspace code as
well.  Even quite big mount table could be scanned for *changes* very
efficiently.  l.e. cache previous contents of /proc/self/mountinfo and
compare with new contents, line-by-line.  Only need to parse the
changed/added/removed lines.

Also it would be pretty easy to throttle the number of updates so
systemd et al. wouldn't hog the system with unnecessary processing.

Thanks,
Miklos