[Ocfs2-users] OCFS2 filesystem hangs with "dirty" locks on internal files

[Charlie Smurthwaite]

On 25/09/2019 19:01, Charlie Smurthwaite wrote:
> Hi,
> 
> I have been trying for some time to get to the bottom of a problem that 
> is causing an OCFS2 filesystem to hang (increasing numbers of file 
> operations hang until the filesystem becomes unusable) seemingly at 
> random, approximately once per day.
> 

Hi,

Just wanted to follow up my own question as I believe I have found the 
solution. After reading some threads about similar issues, I noticed 
that my LocalAlloc size was rather large:

LocalAlloc => State: 1  Descriptor: 0  Size: 27136 bits  Default: 27136 bits

I compared this to the the contiguous free blocks on my filesystem and 
determined that there was almost no such blocks available, despite the 
disk being at only 50% space utilization.

I did not set this manually, but it seems to be the default for my 
filesystem / kernel.

Adding localalloc=16 to my mount options appears to have set a 
localalloc size of 4096 bits (I don't fully understand what this number 
means) and has seemingly resolved my problem, significantly reducing 
disk IO utilization, process IO wait time, and (so far) recurrences of 
the crash.

LocalAlloc => State: 1  Descriptor: 0  Size: 4096 bits  Default: 4096 bits

I have some follow-up questions that are hopefully a bit simpler than my 
original question:

1) Why is the default localalloc size so large? This seems much larger 
than any default I have seen documented.
2) Does this mean that my filesystem is seriously fragmented? If so, is 
there any online tool that can fix this?
3) Is the setting I have chosen reasonable, and is this likely to 
prevent a recurrence of the problem for the foreseeable future?

Thanks!

Charlie