Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: linux-aws (Ubuntu)
       Status: New => Confirmed

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  fstrim and discard operations take too long to complete - Ubuntu 16.04

Status in linux-aws package in Ubuntu:

Bug description:
  1-) Ubuntu Release : Ubuntu 16.04 LTS

  2-) linux-image-

  3-) mkfs.xfs and fstrim -v on a raid0 array using nvme and md should
  not take more than some seconds to complete.

  4-) Formating the raid0 array with xfs took around 2 hours. Running
  fstrim -v on the mount point mounted on top of the raid array took
  around 2 hours.

  How to reproduce the issue:

  - Launch an i3.4xlarge instance on Amazon AWS using an Ubuntu 16.04 AMI ( 
ami-78d2be01 on EU-WEST-1 ), this will generate an instance with one 8Gb EBS 
root volume and two 1.9T SSD drives that are presented to the instance using 
the nvme driver.
  - Compose a raid0 array with the following command :

   # mdadm --create --verbose --level=0 /dev/md0 --raid-devices=2
  /dev/nvme0n1 /dev/nvme1n1

  - When trying to format the raid0 array ( /dev/md0 ) using xfs it
  takes around 2 hours to complete. I tried other AMIs like RHEL7,
  CentOS7 and Ubuntu 18.04 and the time needed was around 2 seconds.

  root@ip-172-31-30-133:~# time mkfs.xfs /dev/md0

  real    120m45.725s
  user    0m0.000s
  sys     0m18.248s

  - Running fstrim -v on a filesystem mounted on top of /dev/md0 can
  take around 2 hours to complete. With other AMIs like RHEL7, CentOS7
  and Ubuntu 18.04 and the time needed was around 2 seconds.

  - When I try the same with any of the nvme SSD devices alone, let's
  say /dev/nvme0n1, the issue doesn't happen.

  - I tried to replicate this issue using LVM and striping, fstrim and
  mkfs.xfs, the tasks complete without taking hours :

  root@ip-172-31-27-69:~# pvcreate /dev/nvme0n1
    Physical volume "/dev/nvme0n1" successfully created

  root@ip-172-31-27-69:~# pvcreate /dev/nvme1n1
    Physical volume "/dev/nvme1n1" successfully created

  root@ip-172-31-27-69:~# vgcreate raid0 /dev/nvme0n1 /dev/nvme1n1
    Volume group "raid0" successfully created

  root@ip-172-31-27-69:~# lvcreate --type striped --stripes 2 --extents 
100%FREE raid0 /dev/nvme0n1 /dev/nvme1n1
    Using default stripesize 64.00 KiB.
    Logical volume "lvol0" created.

  root@ip-172-31-27-69:~# vgchange -ay
    1 logical volume(s) in volume group "raid0" now active

  root@ip-172-31-27-69:~# lvchange -ay /dev/raid0/lvol0

  root@ip-172-31-27-69:~# lvs -a /dev/raid0/lvol0
    LV    VG    Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync 
    lvol0 raid0 -wi-a----- 3.46t
  root@ip-172-31-27-69:~# time mkfs.xfs /dev/raid0/lvol0
  meta-data=/dev/raid0/lvol0       isize=512    agcount=32, agsize=28991664 blks
           =                       sectsz=512   attr=2, projid32bit=1
           =                       crc=1        finobt=1, sparse=0
  data     =                       bsize=4096   blocks=927733248, imaxpct=5
           =                       sunit=16     swidth=32 blks
  naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
  log      =internal log           bsize=4096   blocks=453008, version=2
           =                       sectsz=512   sunit=16 blks, lazy-count=1
  realtime =none                   extsz=4096   blocks=0, rtextents=0

  real    0m2.926s
  user    0m0.180s
  sys     0m0.000s

  root@ip-172-31-27-69:~# mount /dev/raid0/lvol0 /mnt

  root@ip-172-31-27-69:~# time fstrim -v /mnt
  /mnt: 3.5 TiB (3798138650624 bytes) trimmed

  real    0m1.794s
  user    0m0.000s
  sys     0m0.000s

  So the issue only happens when using nvme and md to compose the raid0

  Bellow follows some information that may be useful:

  started formating the md array with mkfs.xfs. Process looks hanged.

  root@ip-172-31-24-66:~# ps aux | grep -i mkfs.xfs
  root       1693 12.0  0.0  12728   968 pts/1    D+   07:54   0:03 mkfs.xfs 

  PID 1693 is in uninterruptible sleep ( D )

  Looking at /proc/7965/stack

  root@ip-172-31-24-66:~# cat /proc/1693/stack
  [<ffffffff8134d8c2>] blkdev_issue_discard+0x232/0x2a0
  [<ffffffff813524bd>] blkdev_ioctl+0x61d/0x7d0
  [<ffffffff811ff6f1>] block_ioctl+0x41/0x50
  [<ffffffff811d89b3>] do_vfs_ioctl+0x2e3/0x4d0
  [<ffffffff811d8c21>] SyS_ioctl+0x81/0xa0
  [<ffffffff81748030>] system_call_fastpath+0x1a/0x1f
  [<ffffffffffffffff>] 0xffffffffffffffff

  Looking at the stack, looks like it's hanged on a discard operation

  root@ip-172-31-24-66:~# ps -flp 1693
  4 D root       1693   1682  2  80   0 -  3182 blkdev 07:54 pts/1    00:00:03 
mkfs.xfs /dev/md0

  root@ip-172-31-24-66:~# cat /proc/1693/wchan

  Process stuck with function --> blkdev_issue_discard

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