From: Martin Steigerwald <martin@lichtvoll.de>
To: Hans van Kranenburg <hans.van.kranenburg@mendix.com>
Cc: Tomasz Chmielewski <tch@virtall.com>,
Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: very poor performance / a lot of writes to disk with space_cache (but not with space_cache=v2)
Date: Wed, 19 Sep 2018 22:04:14 +0200 [thread overview]
Message-ID: <1646602.qIcv3L3msO@merkaba> (raw)
In-Reply-To: <e712843a-d902-97c1-7270-84dfe56c83e1@mendix.com>
Hans van Kranenburg - 19.09.18, 19:58:
> However, as soon as we remount the filesystem with space_cache=v2 -
>
> > writes drop to just around 3-10 MB/s to each disk. If we remount to
> > space_cache - lots of writes, system unresponsive. Again remount to
> > space_cache=v2 - low writes, system responsive.
> >
> > That's a huuge, 10x overhead! Is it expected? Especially that
> > space_cache=v1 is still the default mount option?
>
> Yes, that does not surprise me.
>
> https://events.static.linuxfound.org/sites/events/files/slides/vault20
> 16_0.pdf
>
> Free space cache v1 is the default because of issues with btrfs-progs,
> not because it's unwise to use the kernel code. I can totally
> recommend using it. The linked presentation above gives some good
> background information.
What issues in btrfs-progs are that?
I am wondering whether to switch to freespace tree v2. Would it provide
benefit for a regular / and /home filesystems as dual SSD BTRFS RAID-1
on a laptop?
Thanks,
--
Martin
next prev parent reply other threads:[~2018-09-20 1:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-19 8:43 very poor performance / a lot of writes to disk with space_cache (but not with space_cache=v2) Tomasz Chmielewski
2018-09-19 9:33 ` Qu Wenruo
2018-09-19 12:00 ` Remi Gauvin
2018-09-19 17:58 ` Hans van Kranenburg
2018-09-19 20:04 ` Martin Steigerwald [this message]
2018-09-19 20:11 ` Hans van Kranenburg
2018-09-19 20:30 ` Nikolay Borisov
2018-09-20 0:55 ` Qu Wenruo
2018-09-20 7:46 ` Duncan
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