freebsd stable - Mar 2016 - nfs_getpages: error 4

> On 05 Mar 2016, at 16:33, Eugene Grosbein <eugen at grosbein.net>
wrote:
> 
> 05.03.2016 19:32, Dmitry Sivachenko ?????:
> 
>>>> I am running a number of machines with /home mounted via nfs
(FreeBSD 10.3-PRERELEASE #0 r294799, rw,bg,intr,soft).
>>>> 
>>>> Sometimes I get the following messages in syslog:
>>>> 
>>>> nfs_getpages: error 4
>>>> vm_fault: pager read error, pid NNN (myprog)
>>>> 
>>>> After that I see I lot of processes stuck in "pfault"
state (these are computational processes which use some files from NFS mount),
they use 0% of CPU after that.
>>>> 
>>>> On NFS server machine I see nothing strange in logs.  procstat
-kk for such stuck processes shows:
>>>>  PID    TID COMM             TDNAME           KSTACK
>>>> 85274 102056 myprog           -                mi_switch+0xbe
sleepq_wait+0x3a _sleep+0x287 vm_waitpfault+0x8a vm_fault_hold+0xdd0
vm_fault+0x77 trap_pfault+0x180 trap+0x52c calltrap+0x8
>>>> 
>>>> 
>>>> What can be the reason of this?
>>> 
>>> For example, if some processes running on NFS server box modify
some files "in-place"
>>> and these files are opened by processes running on NFS client, that
could be the reason.
>>> If so, change this so processes updating such files create new
temporary versions of them first
>>> and then rename them atomically.
>>> 
>> 
>> This should not be the case: users are working only on NFS clients.
>> Moreover, the nature of computations is so that each process uses
it's own set of files.
>> 
>> (Forgot to mention in my previous e-mail that these processes can't
be stopped even with kill -9)
> 
> Make sure you use TCP mounts and TSO is disabled.

I do use TCP mount (this is the default).  I will try to disable TSO.

> Try switching between NFSv3/NFSv4 to avoid this bug
As far as I understand, the default is NFSv3 (which should be more stable?).

I can try to switch to NFSv4.

> and to discover what version is broken. And show full mount command/option
set.

I already included mount flags from fstab in my original e-mail:

rw,bg,intr,soft

05.03.2016 20:42, Dmitry Sivachenko ?????:
>> and to discover what version is broken. And show full mount
command/option set.
> I already included mount flags from fstab in my original e-mail:
>
> rw,bg,intr,soft
If that's only options you use, there is another workaround: add options
rsize=1024,wsize=1024 to avoid possible packet reassemply/defragmentation
related bugs.

Again, error 4 is EINTR so you could disable both "soft" and
"intr" options for test.
Anyway, re-read mount_nfs(8) manual page, section BUGS before switch to NFSv4.