Re: MAXACTION exceeded error while using systemtap

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

>  > I think that SystemTap needs some method to periodically (or when memory
>  > pressure arrives) dump the parts of the array to userspace via
>  > relayfs.
> 
> See my previous reply for one way you could do this i.e. the
> kmalloc-stacks example.

Will take a look - seems promising.

>  > relayfs already supports such mechanism with its "sub-buffer" structure,
>  > where the userspace reader is allowed to read full buffers (thus freeing
>  > them afterwards) while the hooks continue to push data to empty or
>  > partially filled buffers.
>  > 
>  > James mentions that
>  > 
>  > "btw MAXACTION really can't work reliably what happens when the box is
>  > underload, say with 4 gigabit nics all being flooded with data, and
>  > you are probing a function in the fast path?
>  > 
>  > Not everyone has a box that can sum 4 billion numbers in less than a minute."
>  > 
>  > relayfs works in two modes once its memory pool is full:
>  > 
>  > - panic's 
>  > - drops new entries
>  > 
>  > I imagine that by using relayfs to send data to userspace one should
>  > automatically get those very important features.
> 
> I'm not sure what you mean - relayfs can be used in either 'overwrite'
> or 'no-overwrite' modes; if its memory pool is full, 'overwrite' mode
> overwrites the oldest entries, while 'no-overwrite' mode drops new
> entries - there should be no 'panic's' anywhere in there.  ;-)

Indeed - there's no "panic" anywhere. Your description is accurate (unlike 
mine's) :)