[solved] Mount/unmount extremely slow (relatively)

Question

When I first installed my system, mounting and unmounting took a relatively unnoticeable amount of time.  Now, mounting a single volume takes about a minute or more per volume, even for tmpfs volumes.  I don't seem to see any other performance problems with my system other than this.
The change happened rather suddenly after I shredded a partition on my drive with one run of bytes (the overall size was about 100 GiB, but I've written several times that onto my drive).  If it makes any difference, the partition was the one that's right to the left of my root partition, but I doubt that anything flowed over.  The disk seems to be operating fine, and when I mount from live CDs, it takes the normal time.
Has anyone ever experienced this kind of problem before?  Do you know what I can do to fix it without reinstalling my system?  I tried reinstalling both the linux and util-linux packages, but that didn't seem to help.
EDIT: Problem's been solved.  To fix:
- Downgrade to util-linux 2.20-2.
- Save everything that you're working on.
- Run the following:
# echo 1 > /proc/sys/kernel/sysrq
# rm -rf /etc/mtab*
- Hold Alt + SysRq and then type out REISUB to reboot.
Last edited by RetroX (2011-10-08 19:09:26)

Answer 1

I'm not sure I'm knowledgeable enough to help too much, but you might like to have a look at the strace command to debug this. It lets you see what calls a program makes to the kernel. You can compare its output on your arch system to what your live CD gives you.
Mounting an ext2 disk on my machine produces this summary (the -c option).  I got fairly varied output each time I ran the command, but hopefully yours is more consistent.
$ strace -c mount /dev/sdb2 /mnt/Backup/
% time seconds usecs/call calls errors syscall
100.00 0.000018 1 18 mmap2
0.00 0.000000 0 101 read
0.00 0.000000 0 4 write
0.00 0.000000 0 20 6 open
0.00 0.000000 0 14 close
0.00 0.000000 0 1 execve
0.00 0.000000 0 3 time
0.00 0.000000 0 1 1 mount
0.00 0.000000 0 1 1 access
0.00 0.000000 0 3 brk
0.00 0.000000 0 2 1 ioctl
0.00 0.000000 0 1 umask
0.00 0.000000 0 11 10 readlink
0.00 0.000000 0 5 munmap
0.00 0.000000 0 1 uname
0.00 0.000000 0 7 mprotect
0.00 0.000000 0 91 _llseek
0.00 0.000000 0 2 prctl
0.00 0.000000 0 2 rt_sigprocmask
0.00 0.000000 0 5 3 stat64
0.00 0.000000 0 2 lstat64
0.00 0.000000 0 11 fstat64
0.00 0.000000 0 3 getuid32
0.00 0.000000 0 2 getgid32
0.00 0.000000 0 3 geteuid32
0.00 0.000000 0 2 getegid32
0.00 0.000000 0 1 set_thread_area
0.00 0.000000 0 1 fadvise64_64
0.00 0.000000 0 1 fstatat64
100.00 0.000018 319 22 total
The summary is probably more interesting initially, but the full dump may be useful later (replace -c with -C for the the full dump combined with the summary).
Edit:
Another similar program you might like to look at is ltrace, which shows library calls (this article put me onto it).
$ ltrace -c mount /dev/sdb2 /mnt/Backup
% time seconds usecs/call calls function
48.11 0.046996 46996 1 blkid_do_safeprobe
22.59 0.022073 49 445 strlen
15.04 0.014694 28 507 strncmp
3.45 0.003375 3375 1 mount
2.37 0.002319 2319 1 blkid_probe_set_device
2.10 0.002048 2048 1 mnt_update_table
1.21 0.001181 1181 1 blkid_free_probe
1.01 0.000989 26 37 __strdup
0.39 0.000383 383 1 mnt_update_set_fs
0.39 0.000382 76 5 __xstat64
0.37 0.000358 358 1 setlocale
0.29 0.000287 26 11 free
0.28 0.000278 139 2 open64
0.25 0.000247 123 2 close
0.20 0.000198 49 4 readlink
0.19 0.000181 25 7 __errno_location
0.14 0.000136 136 1 blkid_evaluate_spec
0.11 0.000109 27 4 strchr
0.11 0.000108 27 4 strtok
0.11 0.000104 26 4 sigdelset
0.10 0.000097 48 2 sigprocmask
0.09 0.000085 28 3 __snprintf_chk
0.08 0.000080 26 3 strrchr
0.07 0.000065 65 1 access
0.06 0.000060 30 2 sigfillset
0.06 0.000054 54 1 __lxstat64
0.05 0.000051 51 1 getuid
0.05 0.000050 50 1 mnt_fs_set_options
0.05 0.000049 49 1 umask
0.05 0.000047 47 1 geteuid
0.05 0.000047 47 1 blkid_new_probe
0.04 0.000040 40 1 blkid_probe_lookup_value
0.04 0.000039 39 1 blkid_probe_set_superblocks_flags
0.04 0.000037 37 1 blkid_probe_enable_superblocks
0.04 0.000036 36 1 mnt_new_fs
0.04 0.000035 35 1 getopt_long
0.03 0.000034 34 1 mnt_init_debug
0.03 0.000034 34 1 mnt_fs_set_source
0.03 0.000033 33 1 bindtextdomain
0.03 0.000032 32 1 mnt_fs_set_fstype
0.03 0.000032 32 1 mnt_free_update
0.03 0.000031 31 1 mnt_new_update
0.03 0.000031 31 1 textdomain
0.03 0.000030 30 1 malloc
0.03 0.000030 30 1 __cxa_atexit
0.03 0.000029 29 1 mnt_free_fs
0.03 0.000028 28 1 mnt_fs_set_target
0.03 0.000028 28 1 mnt_update_get_mflags
100.00 0.097690 1074 total
Last edited by splondike (2011-10-06 12:21:07)