From: Duncan <1i5t5.duncan@cox.net>
To: linux-btrfs@vger.kernel.org
Subject: Re: Query about proposed dedup patches and behaviours
Date: Fri, 15 Jan 2016 01:47:21 +0000 (UTC) [thread overview]
Message-ID: <pan$b0586$d2b2b229$291cbb7b$f3802e23@cox.net> (raw)
In-Reply-To: 5697F9E7.1020004@gmail.com
Austin S. Hemmelgarn posted on Thu, 14 Jan 2016 14:41:27 -0500 as
excerpted:
> On 2016-01-14 14:26, Liu Bo wrote:
>> On Thu, Jan 14, 2016 at 11:46:33AM -0500, Austin S. Hemmelgarn wrote:
>>> On 2016-01-14 11:13, James Hogarth wrote:
>>>> Finally what's the present situation with regards to defragmentation
>>>> and deduplication? Is it safe to turn on autodefrag now when using
>>>> snapshots and duperemove? What should the behaviour be with the
>>>> proposed 4.5 dedup patches if both inline dedup and autodefrag are
>>>> enabled as mount options?
>>> I'm not entirely certain how deduplication would interact with any
>>> form of defragmentation. I'm pretty certain though that autodefrag
>>> does properly handle snapshots, such that the reflinks aren't broken,
>>> and it's the original copy that gets any shared extents defragmented
>>> into it.
>>
>> If it refers to snapshot-aware defrag, it's been disabled, so now btrfs
>> will not maintain reflinks between snapshots.
>>
> I was under the impression that autodefrag had been done separately from
> the snapshot-aware manually triggered defrag, and that it's always been
> snapshot aware.
Hugo should really explain as he was the one that said that, but upon
looking into it, he found that while he was correct in a sense, his
reasoning was a bit narrow, and autodefrag isn't snapshot aware in the
wider context.
Without attempting to explain his reasoning as I think I sort of
understand it but not well enough to try to explain, autodefrag isn't
snapshot aware and will break reflinks, but due to $reasons, autodefrag's
damage to reflinking apparently isn't as bad as manual defrag.
That's the best I can do to explain the situation. In general,
autodefrag remains bad for reflinks, but apparently not h***-bad, as
manual defrag is.
--
Duncan - List replies preferred. No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master." Richard Stallman
next prev parent reply other threads:[~2016-01-15 1:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-14 16:13 Query about proposed dedup patches and behaviours James Hogarth
2016-01-14 16:46 ` Austin S. Hemmelgarn
2016-01-14 19:26 ` Liu Bo
2016-01-14 19:41 ` Austin S. Hemmelgarn
2016-01-15 1:47 ` Duncan [this message]
2016-01-15 9:33 ` James Hogarth
2016-01-15 12:18 ` Duncan
2016-01-20 15:33 ` Interjection: autodefrag mount option aye, nae? Al
2016-01-20 15:39 ` Austin S. Hemmelgarn
2016-01-20 18:39 ` Duncan
2016-01-21 20:59 ` Kai Krakow
2016-01-22 12:14 ` Austin S. Hemmelgarn
2016-01-22 19:43 ` Kai Krakow
2016-01-23 22:11 ` Query about proposed dedup patches and behaviours Mark Fasheh
2016-01-24 5:12 ` Duncan
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