ZFS txg implementation flaw

[Slawa Olhovchenkov]

On Mon, Oct 28, 2013 at 10:45:02AM -0700, aurfalien wrote:

> 
> On Oct 28, 2013, at 2:28 AM, Slawa Olhovchenkov wrote:
> 
> > I can be wrong.
> > As I see ZFS cretate seperate thread for earch txg writing.
> > Also for writing to L2ARC.
> > As result -- up to several thousands threads created and destoyed per
> > second. And hundreds thousands page allocations, zeroing, maping
> > unmaping and freeing per seconds. Very high overhead.
> > 
> > In systat -vmstat I see totfr up to 600000, prcfr up to 200000.
> > 
> > Estimated overhead -- 30% of system time.
> > 
> > Can anybody implement thread and page pool for txg?
> 
> Would lowering vfs.zfs.txg.timeout be a way to tame or mitigate this?

vfs.zfs.txg.timeout: 5

Only x5 lowering (less in real case with burst writing). And more fragmentation on writing and etc.