[QUESTION]about libmount library performance problems

[QUESTION]about libmount library performance problems

[chenditang]

Hi util-linux@vger.kernel.org

I have 1 question which need confirm.

  in the RHEL7.0alpha version
	nfs-utils-1.2.5-3.el7.x86_64  --> use mount_libmount.c
	util-linux-2.20.1-2.el7.x86_64
  when umount a NFS directory, the mnt_table_parse_mtab() function will merge user options(/run/mount/utab) 
into mountinfo(/proc/self/mountinfo)from kernel. if the mount number is large, leading to umount a directory
time-consuming. the complexity of the algorithm is O(n(n+1)/2).

    but in the old version(RHEL6.3GA/nfs-utils-1.2.3-26.el6.x86_64(use mount.c)), only according to the parameters of umount command, 
find the corresponding record in the /etc/mtab file

  Question)*:* merg the tow file are necessary for umount a dir?

TEST LOG:
#cat mount_test.sh
#!/bin/bash
mount=/tmp/mount
if [ ! -d $mount ]; then
    mkdir -p $mount
fi
for dir in {1..8000}; do
    if [ ! -d $mount/$dir ]; then
        mkdir -p $mount/$dir
    fi
    echo mount $dir
    mount -t nfs 127.0.0.1:/ $mount/$dir
done 

# time umount /tmp/mount/1    --------->RHEL7.0alpha
real    0m2.395s
user    0m1.640s        
sys     0m0.466s

# time umount /tmp/mount/1    --------->RHEL6.3GA
real	0m0.159s
user	0m0.042s        
sys	0m0.114s


thanks.

Re: [QUESTION]about libmount library performance problems

[Karel Zak]

On Tue, Sep 25, 2012 at 10:02:35AM +0800, chenditang wrote:
> I have 1 question which need confirm.
> 
>   in the RHEL7.0alpha version
> 	nfs-utils-1.2.5-3.el7.x86_64  --> use mount_libmount.c
> 	util-linux-2.20.1-2.el7.x86_64
>   when umount a NFS directory, the mnt_table_parse_mtab() function will merge user options(/run/mount/utab) 
> into mountinfo(/proc/self/mountinfo)from kernel. if the mount number is large, leading to umount a directory
> time-consuming. the complexity of the algorithm is O(n(n+1)/2).

 Yes, maybe we can somehow improve the file format and the algorithm,
 suggestions?

>     but in the old version(RHEL6.3GA/nfs-utils-1.2.3-26.el6.x86_64(use mount.c)), only according to the parameters of umount command, 
> find the corresponding record in the /etc/mtab file

 But we don't have mtab file in RHEL7 anymore, so we have to store the
 userspace specific mount options somewhere... (/run/mount/utab).  The
 solution is to minimize number of information we have to maintain in
 userspace.

 Unfortunately it seems that for example on my system we duplicate the
 information:

      utab:  retrans=20,addr=192.168.111.1

 mountinfo:  rw,vers=3,rsize=131072,wsize=131072,namlen=255,hard,proto=tcp,timeo=600,
             retrans=20,sec=sys,mountaddr=192.168.111.1,mountvers=3,mountport=39755,
             mountproto=udp,local_lock=none,addr=192.168.111.1

 (see retrans= and addr=)

 Maybe we can detect this situation and don't store duplicate options
 in userspace. The question is what happen with retrans= and addr=
 after remount. If I good remember there was any reason to maintain
 these stuff in userspace. Chuck?

>   Question)*:* merg the tow file are necessary for umount a dir?

 I guess nfs umount needs the addr= info.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: [QUESTION]about libmount library performance problems

[Karel Zak]

On Tue, Sep 25, 2012 at 12:10:31PM +0200, Karel Zak wrote:
> On Tue, Sep 25, 2012 at 10:02:35AM +0800, chenditang wrote:
> >   Question)*:* merg the tow file are necessary for umount a dir?

 Ah, do you mean -- why we need to merge all the entries when we want
 to work with only one mountpoint? That's good question ;-) I'll try
 to improve the code...

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: [QUESTION]about libmount library performance problems

[Karel Zak]

On Tue, Sep 25, 2012 at 12:31:42PM +0200, Karel Zak wrote:
> > On Tue, Sep 25, 2012 at 10:02:35AM +0800, chenditang wrote:
> > >   Question)*:* merg the tow file are necessary for umount a dir?
> 
>  Ah, do you mean -- why we need to merge all the entries when we want
>  to work with only one mountpoint? That's good question ;-) I'll try
>  to improve the code...

 Improved:

   old version:
        time ./umount /tmp/mount/2255

        real    0m1.254s
        user    0m1.002s
        sys     0m0.238s

    new version:
        time ./umount /tmp/mount/2244

        real    0m0.332s
        user    0m0.111s
        sys     0m0.218s



 Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com