From: Kai Krakow <hurikhan77@gmail.com>
To: linux-btrfs@vger.kernel.org
Subject: Re: space_cache=v2 on root fs
Date: Mon, 18 Jan 2016 22:04:24 +0100 [thread overview]
Message-ID: <20160118220424.0a77dc71@jupiter.sol.kaishome.de> (raw)
In-Reply-To: 20160118191243.GA321@x4
Am Mon, 18 Jan 2016 20:12:43 +0100
schrieb Markus Trippelsdorf <markus@trippelsdorf.de>:
> On 2016.01.18 at 19:27 +0100, Markus Trippelsdorf wrote:
> > Hi,
> >
> > while testing the new space_cache=v2 mount option it looks like my
> > root fs doesn't automatically create the new space cache.
> >
> > I'm using the following /etc/fstab:
> >
> > UUID=7ef56edc-673e-452e-9e05-3fabf074168b /
> > btrfs noatime,compress=lzo,space_cache=v2 0 0
> > UUID=6b7d75bf-3d12-409c-88ed-500ac6b78510 /var
> > btrfs compress=lzo,space_cache=v2 0 0
> > UUID=24cee7e4-9093-4f86-aa73-d8a59d7f3c6c /var/tmp
> > btrfs compress=lzo,space_cache=v2 0 0
> >
> > During first mount the space cache was created for /var (/dev/sdb2)
> > and /var/tmp (/dev/sda3), but apparently not for / (/dev/sdc3):
> >
> > Jan 18 18:48:18 x4 kernel: BTRFS info (device sdb2): enabling free
> > space tree Jan 18 18:48:18 x4 kernel: BTRFS info (device sdb2):
> > using free space tree Jan 18 18:48:18 x4 kernel: BTRFS: creating
> > free space tree Jan 18 18:48:18 x4 kernel: BTRFS info (device
> > sdb2): setting 1 ro feature flag Jan 18 18:48:18 x4 kernel: BTRFS:
> > checking UUID tree Jan 18 18:48:18 x4 kernel: BTRFS info (device
> > sda3): enabling free space tree Jan 18 18:48:18 x4 kernel: BTRFS
> > info (device sda3): using free space tree Jan 18 18:48:18 x4
> > kernel: BTRFS: has skinny extents Jan 18 18:48:18 x4 kernel: BTRFS:
> > detected SSD devices, enabling SSD mode Jan 18 18:48:18 x4 kernel:
> > BTRFS: creating free space tree Jan 18 18:48:18 x4 kernel: BTRFS
> > info (device sda3): setting 1 ro feature flag Jan 18 18:48:18 x4
> > kernel: BTRFS: checking UUID tree Jan 18 18:48:22 x4 kernel: BTRFS
> > info (device sdc3): enabling free space tree Jan 18 18:48:22 x4
> > kernel: BTRFS info (device sdc3): using free space tree
> >
> > During subsequent boots the "enabling free space tree" message is
> > repeated every time for the root fs.
> >
> > Jan 18 18:53:48 x4 kernel: BTRFS info (device sdb2): using free
> > space tree Jan 18 18:53:48 x4 kernel: BTRFS info (device sda3):
> > using free space tree Jan 18 18:53:52 x4 kernel: BTRFS info (device
> > sdc3): enabling free space tree Jan 18 18:53:52 x4 kernel: BTRFS
> > info (device sdc3): using free space tree
>
> To answer my own question. Adding "rw rootflags=space_cache=v2" to the
> GRUB kernel entry fixes the issue...
This is because the contents of /etc/fstab are not available during
first mount at boot time - for obvious reasons. Actually, the entry for
rootfs in /etc/fstab is more or less a no-op and only there to satisfy
some legacy tools. Some initramfs generators may also use this to
construct a proper grub cmdline. At least dracut seems to rely on other
mechanics, tho. So it's probably obsolete.
There's only one point when it is used: During remount of the fs during
system initialization. But only some mount options can change during
remount, I imagine space_cache is not part of this.
Due to this remount, it is best to keep both in sync: grub cmdline and
fstab.
I think systemd has some efforts of obsoleting the rootfs line from
fstab, however I'm not sure what's the progress here. I still use it
because last time I tried removing it, it had strange effects.
--
Regards,
Kai
Replies to list-only preferred.
prev parent reply other threads:[~2016-01-18 21:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-18 18:27 space_cache=v2 on root fs Markus Trippelsdorf
2016-01-18 19:12 ` Markus Trippelsdorf
2016-01-18 21:04 ` Kai Krakow [this message]
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=20160118220424.0a77dc71@jupiter.sol.kaishome.de \
--to=hurikhan77@gmail.com \
--cc=linux-btrfs@vger.kernel.org \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.