[Bug 1878605] [NEW] Slow performance during large writes

[Marius Flage]

Public bug reported:

When performing a large write to a NFS share, then all other I/O
operations towards this share is hung/slowed down until the large write
operation is completed. In 20.04 this seems to be fixed. In 16.04 this
was terrible and all other I/O operations was hung until the write had
completed, in 18.04 this was slightly better, but still all I/O
operations were slowed down significantly.

Is this a known issue? Would it be possible to backport whatever was
changed between 18.04 and 20.04 to get the same fix in 18.04?

Example on how this is on 18.04:

# echo "baseline test - no write operation currently"
baseline test - no write operation currently
# time ls
... <directory listing omitted>

real	0m0.009s
user	0m0.005s
sys	0m0.001s
# dd if=/dev/zero of=test.img bs=1M count=10000 &
[1] 15489
# echo "write operation"
write operation
# time ls
... <directory listing omitted>

real	1m28.947s
user	0m0.000s
sys	0m0.970s
# 10000+0 records in
10000+0 records out
10485760000 bytes (10 GB, 9.8 GiB) copied, 90.6114 s, 116 MB/s

[1]+  Done                    dd if=/dev/zero of=test.img bs=1M
count=10000

Here is the output from the 'mount'-command:

type nfs4
(rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.102.150.10,local_lock=none,addr=10.102.150.35)

With 20.04 this seems to be working just fine.

** Affects: nfs-utils (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1878605

Title:
  Slow performance during large writes

Status in nfs-utils package in Ubuntu:
  New

Bug description:
  When performing a large write to a NFS share, then all other I/O
  operations towards this share is hung/slowed down until the large
  write operation is completed. In 20.04 this seems to be fixed. In
  16.04 this was terrible and all other I/O operations was hung until
  the write had completed, in 18.04 this was slightly better, but still
  all I/O operations were slowed down significantly.

  Is this a known issue? Would it be possible to backport whatever was
  changed between 18.04 and 20.04 to get the same fix in 18.04?

  Example on how this is on 18.04:

  # echo "baseline test - no write operation currently"
  baseline test - no write operation currently
  # time ls
  ... <directory listing omitted>

  real	0m0.009s
  user	0m0.005s
  sys	0m0.001s
  # dd if=/dev/zero of=test.img bs=1M count=10000 &
  [1] 15489
  # echo "write operation"
  write operation
  # time ls
  ... <directory listing omitted>

  real	1m28.947s
  user	0m0.000s
  sys	0m0.970s
  # 10000+0 records in
  10000+0 records out
  10485760000 bytes (10 GB, 9.8 GiB) copied, 90.6114 s, 116 MB/s

  [1]+  Done                    dd if=/dev/zero of=test.img bs=1M
  count=10000

  Here is the output from the 'mount'-command:

  type nfs4
  (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.102.150.10,local_lock=none,addr=10.102.150.35)

  With 20.04 this seems to be working just fine.

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