[Bug 194513] zfs recv hangs in state kmem arena

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=194513

mgoroff at quorum.net changed:

           What    |Removed                     |Added
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                 CC|                            |mgoroff at quorum.net

--- Comment #13 from mgoroff at quorum.net ---
We are encountering what appears to be the same issue on a large production
server running 10.2-RELEASE. The machine has 128G of RAM and vfs.zfs.arc_max is
set to 100G. I have a zfs recv currently stuck waiting on kmem arena. When this
problem occurs, the ARC starts rapidly shrinking down to vfs.zfs.arc_min (13G
in our case) but the process will remain blocked for a long period of time
(hours) even though top shows free memory at 104G.

ps -l for the process shows:

UID   PID  PPID CPU PRI NI   VSZ  RSS MWCHAN   STAT TT     TIME COMMAND
  0 37892 37814   0  20  0 42248 3428 kmem are D     1  0:04.16 zfs recv -u -d
ezdata2

while procstat -kk -p 37892 shows:

  PID    TID COMM             TDNAME           KSTACK                       
37892 101149 zfs              -                mi_switch+0xe1 sleepq_wait+0x3a
_cv_wait+0x16d vmem_xalloc+0x568 vmem_alloc+0x3d kmem_malloc+0x33
uma_large_malloc+0x49 malloc+0x43 dmu_recv_stream+0x114 zfs_ioc_recv+0x955
zfsdev_ioctl+0x5ca devfs_ioctl_f+0x139 kern_ioctl+0x255 sys_ioctl+0x140
amd64_syscall+0x357 Xfast_syscall+0xfb

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