[Pkg-xen-devel] [Xen-devel] [admin] [BUG] task jbd2/xvda4-8:174 blocked for more than 120 seconds.

[Hans van Kranenburg]

On 2/11/19 2:37 AM, Dongli Zhang wrote:
> 
> On 2/10/19 12:35 AM, Samuel Thibault wrote:
>>
>> Hans van Kranenburg, le sam. 09 févr. 2019 17:01:55 +0100, a ecrit:
>>>> I have forwarded the original mail: all VM I/O get stuck, and thus the
>>>> VM becomes unusable.
>>>
>>> These are in many cases the symptoms of running out of "grant frames".
>>
>> Oh!  That could be it indeed.  I'm wondering what could be monopolizing
>> them, though, and why +deb9u11 is affected while +deb9u10 is not.  I'm
>> afraid increasing the gnttab max size to 32 might just defer filling it
>> up.
>>
>>>   -# ./xen-diag  gnttab_query_size 5
>>>   domid=5: nr_frames=11, max_nr_frames=32
>>
>> The current value is 31 over max 32 indeed.
> 
> Assuming this is grant v1, there are still 4096/8=512 grant references available
> (32-31=1 frame available). I do not think the I/O hang can be affected by the
> lack of grant entry.

I suspect that 31 measurement was taken when the domU was not hanging yet.

> If to increase the max frame to 64 takes effect, it is weird why the I/O would
> hang when there are still 512 entries available.
> 
>>> With Xen 4.8, you can add gnttab_max_frames=64 (or another number, but
>>> higher than the default 32) to the xen hypervisor command line and reboot.
>>
>> admin@: I made the modification in the grub config. We can probably try
>> to reboot with the newer hypervisor, and monitor that value.

K