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Subject: Re: ZFS txg implementation flaw
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From: aurfalien <aurfalien@gmail.com>
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Date: Mon, 28 Oct 2013 11:25:25 -0700
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To: Slawa Olhovchenkov <slw@zxy.spb.ru>
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On Oct 28, 2013, at 11:16 AM, Slawa Olhovchenkov wrote:

> On Mon, Oct 28, 2013 at 10:45:02AM -0700, aurfalien wrote:
>=20
>>=20
>> On Oct 28, 2013, at 2:28 AM, Slawa Olhovchenkov wrote:
>>=20
>>> 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.
>>>=20
>>> In systat -vmstat I see totfr up to 600000, prcfr up to 200000.
>>>=20
>>> Estimated overhead -- 30% of system time.
>>>=20
>>> Can anybody implement thread and page pool for txg?
>>=20
>> Would lowering vfs.zfs.txg.timeout be a way to tame or mitigate this?
>=20
> vfs.zfs.txg.timeout: 5
>=20
> 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