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

[Eric Desrochers]

Hi Hua,

Thanks for the quick debdiffs update. It looks good to me now but I
still have 2 concerned :

#1 - Why the quilt patch isn't apply on top ? Any particular reason ?
If there is a reason it's totally fine, I just want to raise all the possible SRU team concerned before the final upload in order to have a smooth SRU.

#2 - A "quilt push -a" command revealed a few "Hunk # succeeded at ...."

Seems like "daemon/automount.c" was successfully patched, but it is now
patched with an offset of 28 lines (when it applies cleanly when your
patch is absent). Seems like the current position of your patch is
influencing the application of others.

So basically it returns to concern #1, is this the appropriate position
for this patch ? If yes, why (SRU team will most likely ask the same
question, so we better have an answer for them) ? If the answer is no,
then please make sure your patch is the topmost patch on the current
stack of applied patches.

Validation can be made by doing this command :

$ quilt top
<YOUR_PATCH>

* With your patch in current position :
Applying patch remove-kernel-mount.nfs-version-check.patch
patching file daemon/automount.c
Hunk #2 succeeded at 1397 (offset 28 lines).
Hunk #3 succeeded at 2062 (offset 28 lines).
patching file include/mounts.h
patching file modules/replicated.c
patching file lib/mounts.c


* Without your patch :
Applying patch remove-kernel-mount.nfs-version-check.patch
patching file daemon/automount.c
patching file include/mounts.h
patching file modules/replicated.c
patching file lib/mounts.c

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https://bugs.launchpad.net/bugs/1686679

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

Status in autofs5 package in Ubuntu:
  Fix Released
Status in autofs5 source package in Xenial:
  In Progress
Status in autofs5 source package in Yakkety:
  In Progress

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.

  * What releases to fix

  $ git tag --contains 67e7d613a4b09eeffc57ab44a7acb52027d897b2
  release_5_1_2

  $ rmadison autofs5
   autofs5 | 5.1.1-1ubuntu3 | xenial | all
   autofs5 | 5.1.1-1ubuntu3 | yakkety | all
   autofs5 | 5.1.2-1ubuntu1 | zesty | all
   autofs5 | 5.1.2-1ubuntu1 | artful | all

  $ rmadison -u debian autofs5
   autofs5    | 5.1.2-1        | unstable        | all

  - Ubuntu : Only Xenial and Yakkety are affected.
  Zesty and Artful already has the upstream fix because they are at version 5.1.2.

  - Debian : unstable also has the fix already.

  [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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