ZFS txg implementation flaw

[aurfalien]

On Oct 28, 2013, at 11:16 AM, Slawa Olhovchenkov wrote:

> 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.

So leave it default in other words.

Good to know.

- aurf