Bug#827322: multipath-tools: Not all paths discovered when large number of paths are present

[Andrew Patterson]

On 06/15/2016 08:43 AM, Ritesh Raj Sarraf wrote:
> Control: tag -1 moreinfo
> 
> On Tue, 2016-06-14 at 17:30 -0600, Andrew Patterson wrote:
>> There is no output in dmesg.
>>
>> Changing /proc/sys/fs/aio-max-nr from the default 65536 to 1048576
>> seems to help. With this change, I can go up to 256 LUNs (1024 paths)
>> with no problems.
>>
>> I have seen similar issues in earlier versions of multipath-tools.
> 
> Thank you for bringing this up, and the pointer. In multipath.conf there was a
> directive added for something similar.
> 
> 
>        max_fds          Specify  the  maximum  number of file descriptors that
>                         can be opened by multipath and  multipathd.   This  is
>                         equivalent  to ulimit -n. A value of max will set this
>                         to the system limit from /proc/sys/fs/nr_open. If this
>                         is  not  set,  the maximum number of open fds is taken
>                         from the calling process. It is usually  1024.  To  be
>                         safe,  this  should  be  set  to the maximum number of
>                         paths plus 32, if that number is greated than 1024.
> 
> 
> It seems to be inline with what aio-max-nr documentation says.
> 
> ==============================================================
> 
> aio-nr & aio-max-nr:
> 
> aio-nr is the running total of the number of events specified on the
> io_setup system call for all currently active aio contexts.  If aio-nr
> reaches aio-max-nr then io_setup will fail with EAGAIN.  Note that
> raising aio-max-nr does not result in the pre-allocation or re-sizing
> of any kernel data structures.
> 
> ==============================================================
> 
> 
> Have you tried it with the "max_fds" option set ?
> 
> 

Thanks for reminding me about max_fds. At boot:

# cat /proc/sys/fs/nr_open
1048576

and

# multipath -t | grep max_fds
        max_fds "max"

So this should already be set to 1048576. I tried the test again after
setting max_fd 1048576 in /etc/multipath.conf and got the same
behavior.


--
Andrew Patterson
Hewlett-Packard Enterprise