Re: Boot speed/mount time regression with 3.4.0-rc2

[Josef Bacik <josef@redhat.com>]

On Wed, Apr 11, 2012 at 11:38:33AM -0500, Chester wrote:
> On Mon, Apr 9, 2012 at 10:53 AM, Calvin Walton <calvin.walton@kepstin=
=2Eca> wrote:
> >
> > Hi,
> >
> > I have a system that's using a dracut-generated initramfs to mount =
a
> > btrfs root. After upgrading to kernel 3.4.0-rc2 to test it out, I'v=
e
> > noticed that the process of mounting the root filesystem takes much
> > longer with 3.4.0-rc2 than it did with 3.3.1 - nearly 30 seconds sl=
ower!
> >
> > Does anyone have any ideas? I'm going to try bisecting the issue to=
 see
> > if I can narrow down the cause. I've included excerpts from dmesg o=
f the
> > bad and good kernels here, and attached the complete dmesg from the=
 bad
> > kernel, in case it has anything interesting that I've trimmed out h=
ere.
> >
> > slow:
> > [ =A0 =A00.000000] Linux version 3.4.0-rc2 (cwalton@ayu) (gcc versi=
on 4.6.3
> > (Exherbo gcc-4.6.3) ) #57 SMP PREEMPT Mon Apr 9 11:19:43 EDT 2012
> > [ =A0 =A00.000000] Command line:
> > root=3DUUID=3D43969cd0-4aca-4297-bfbe-952a692f7d55
> > rootflags=3Dsubvolid=3D262,compress=3Dlzo,autodefrag,space_cache,in=
ode_cache,noatime
> > mtrr_chunk_size=3D512M quiet
> > <snip>
> > [ =A0 =A01.058257] udevd[701]: starting version 182
> > [ =A0 =A01.389606] device label Linux data devid 1 transid 611923 /=
dev/sda4
> > [ =A0 =A01.498659] dracut: Checking, if btrfs device complete
> > [ =A0 =A01.644808] device label Linux data devid 1 transid 611923 /=
dev/sda4
> > [ =A0 =A01.647993] btrfs: disk space caching is enabled
> > [ =A0 =A02.180836] device label Linux data devid 1 transid 611923 /=
dev/sda4
> > [ =A0 =A02.181663] btrfs: use lzo compression
> > [ =A0 =A02.181667] btrfs: enabling auto defrag
> > [ =A0 =A02.181670] btrfs: enabling inode map caching
> > [ =A0 =A02.181672] btrfs: disk space caching is enabled
> > [ =A0 =A02.697845] dracut: Checking btrfs:
> > /dev/disk/by-uuid/43969cd0-4aca-4297-bfbe-952a692f7d55
> > [ =A0 =A02.699999] dracut: trying to mount
> > /dev/disk/by-uuid/43969cd0-4aca-4297-bfbe-952a692f7d55
> > [ =A0 =A02.702637] device label Linux data devid 1 transid 611923 /=
dev/sda4
> > [ =A0 =A02.704376] btrfs: disk space caching is enabled
> > [ =A0 =A03.081720] dracut: btrfs:
> > /dev/disk/by-uuid/43969cd0-4aca-4297-bfbe-952a692f7d55 is clean
> > [ =A0 29.934639] dracut: Remounting
> > /dev/disk/by-uuid/43969cd0-4aca-4297-bfbe-952a692f7d55 with -o
> > subvolid=3D262,compress=3Dlzo,autodefrag,space_cache,inode_cache,no=
atime,ro
> > [ =A0 29.936810] device label Linux data devid 1 transid 611926 /de=
v/sda4
> > [ =A0 29.937720] btrfs: use lzo compression
> > [ =A0 29.937726] btrfs: enabling auto defrag
> > [ =A0 29.937733] btrfs: enabling inode map caching
> > [ =A0 29.937735] btrfs: disk space caching is enabled
> > [ =A0 30.388066] dracut: Mounted root filesystem /dev/sda4
> > [ =A0 30.461884] dracut: Switching root
> > [ =A0 31.241729] udevd[1322]: starting version 182
> > [ =A0 31.422905] btrfs: use lzo compression
> > [ =A0 31.422909] btrfs: enabling auto defrag
> > [ =A0 31.422913] btrfs: enabling inode map caching
> > [ =A0 31.422915] btrfs: disk space caching is enabled
> >
> > vs fast:
> > [ =A0 =A00.000000] Linux version 3.3.1 (cwalton@ayu) (gcc version 4=
=2E6.3
> > (Exherbo gcc-4.6.3) ) #53 SMP PREEMPT Wed Apr 4 01:20:47 EDT 2012
> > [ =A0 =A00.000000] Command line:
> > root=3DUUID=3D43969cd0-4aca-4297-bfbe-952a692f7d55
> > rootflags=3Dsubvolid=3D262,compress=3Dlzo,autodefrag,space_cache,in=
ode_cache,noatime
>=20
> Calvin, I noticed that you have the space_cache mount option set. I
> remember josef saying that it is a one-time option where it's a
> permanent change after mounting for the first time, therefore each
> subsequent mount will not require the option. In fact, if the option
> is specified again, the space_cache is reset.
>=20
> Is this still up-to-date info?
>=20

No you can leave space_cache set, there's another option for resetting =
the space
cache, clear_cache iirc.  Thanks,

Josef
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