From: Mitch Harder <mitch.harder@sabayonlinux.org>
To: Brendan Hide <brendan@swiftspirit.co.za>
Cc: Martin <m_btrfs@ml1.co.uk>, linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: What to do about snapshot-aware defrag
Date: Sun, 1 Jun 2014 22:07:13 -0500 [thread overview]
Message-ID: <CAKcLGm_Ou57upZUvUJT0RH3trVAH3DgWJp2k38q9P6vAkgjwKQ@mail.gmail.com> (raw)
In-Reply-To: <538A6B15.3080609@swiftspirit.co.za>
On Sat, May 31, 2014 at 6:51 PM, Brendan Hide <brendan@swiftspirit.co.za> wrote:
> On 2014/05/31 12:00 AM, Martin wrote:
>>
>> OK... I'll jump in...
>>
>> On 30/05/14 21:43, Josef Bacik wrote:
>>>
>>> [snip]
>>>
>>> Option 1: Only relink inodes that haven't changed since the snapshot was
>>> taken.
>>>
>>> Pros:
>>> -Faster
>>> -Simpler
>>> -Less duplicated code, uses existing functions for tricky operations so
>>> less likely to introduce weird bugs.
>>>
>>> Cons:
>>> -Could possibly lost some of the snapshot-awareness of the defrag. If
>>> you just touch a file we would not do the relinking and you'd end up
>>> with twice the space usage.
>>
>> [...]
>>
>>
>> Obvious way to go for fast KISS.
>
>
> I second this - KISS is better.
>
> Would in-band dedupe resolve the issue with losing the "snapshot-awareness
> of the defrag"? I figure that if someone absolutely wants everything deduped
> efficiently they'd put in the necessary resources (memory/dedicated SSD/etc)
> to have in-band dedupe work well.
>
>> One question:
>>
>> Will option one mean that we always need to mount with noatime or
>> read-only to allow snapshot defragging to do anything?
>
>
When snapshot-aware defrag first came out, I was convinced it was a
"must-have" capability for nearly everybody using btrfs. But, the
more I look at my work load and common practices with btrfs, the more
I am wondering just how often snapshot-aware defrag was actually doing
something for me.
I use a lot of snapshots. But for the most part, once I touch a file
in my current subvolume, the whole file needs to be COW-ed from it's
previous version.
Now that we have a working sysfs, I wonder if we could implement some
counters to track how often snapshot-aware defrag would have run. I
might be surprised at how much it was doing.
---
Regards,
Mitch Harder
next prev parent reply other threads:[~2014-06-02 3:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-30 20:43 What to do about snapshot-aware defrag Josef Bacik
2014-05-30 22:00 ` Martin
2014-05-31 23:51 ` Brendan Hide
2014-06-01 1:52 ` Duncan
2014-06-02 3:07 ` Mitch Harder [this message]
2014-06-02 13:19 ` Josef Bacik
2014-06-02 13:22 ` Josef Bacik
2014-06-03 23:54 ` Martin
2014-06-04 9:19 ` Erkki Seppala
2014-06-04 13:15 ` Martin
2014-06-04 19:33 ` Chris Murphy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAKcLGm_Ou57upZUvUJT0RH3trVAH3DgWJp2k38q9P6vAkgjwKQ@mail.gmail.com \
--to=mitch.harder@sabayonlinux.org \
--cc=brendan@swiftspirit.co.za \
--cc=linux-btrfs@vger.kernel.org \
--cc=m_btrfs@ml1.co.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).