[Bug 1686679] Re: [SRU] Ubuntu16.04 : autofs takes extreamly long with large number of direct maps

[Hua Zhang]

Hi Christian,

Sorry for late response because of sprint and pto during this period, I
have updated the bug description and debdiff to address your concerns,
many thanks.

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Title:
  [SRU] Ubuntu16.04 : autofs takes extreamly long with large number of
  direct maps

Status in autofs5 package in Ubuntu:
  Fix Released
Status in autofs5 source package in Xenial:
  New
Status in autofs5 source package in Yakkety:
  New

Bug description:
  [Impact]

  autofs service in xenial takes extremely long time since it parses the 
  mount table /etc/mtab in contained_in_local_fs() to determine if the mount 
  patch would be created on a local file system, that means startup process will read /etc/mtab for every mount, so the performance is extremely low. The customer is complaining about this point, we need to backport the 
  following upstream patch.

  https://git.kernel.org/pub/scm/linux/storage/autofs/autofs.git/commit/?id=67e7d613a4b09eeffc57ab44a7acb52027d897b2

  This fix patch removes contained_in_local_fs, and use fs.f_type in is_remote_fstype() to determine if the mount patch would be created on a
   local file system instead.

  [Test Case]

   * Create an autofs direct mount map with large direct mappings (eg:
  8k), below is the test script I used.

  echo "/-      auto.direct        --timeout 60" >> /etc/auto.master
  END=8000
  for i in $(seq 1 $END); do echo $i; echo "/test/samba/test"$i" -fstype=cifs,rw,username=hua,password=password ://192.168.99.169/share" >> /etc/auto.direct; done

   * Start autofs service to see if it will take too much time, below is my
   result before/after applying the fix patch.

  root at node1:~# time service autofs start
  real	3m5.481s
  user	0m0.256s
  sys	0m0.080s
  root at node1:~# time service autofs start
  real	0m0.833s
  user	0m0.000s
  sys	0m0.004s

  [Regression Potential]

  * We are well aware of the principle of this fix patch - avoiding parsing 
  the mount table to improve startup time, so seems infinitely better for 
  all cases.

  * This fix from upstream has been backported into Redhat as well, and both
   me and customer have positive test results with automount start timings.

  [Other Info]

  * Redhat [1] also already backported the following patch, see: https://bugzilla.redhat.com/show_bug.cgi?id=1440769
  * This mailing list also discussed this problem, see: http://www.spinics.net/lists/autofs/msg01161.html

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