On 1/24/22 05:14, Chris Murphy wrote:
On Sun, Jan 23, 2022 at 5:30 PM Robert-André Mauchin <zebob.m@xxxxxxxxx> wrote:
Hi,
So I have an annoying bug that started near the beginnings of F35.
My papirus-icon-theme became very slow to install:
https://bugzilla.redhat.com/show_bug.cgi?id=2029709#c18
During the installation, all the files are copied, then renamed by rpm
(no idea why it works like this).
It works fast in a Mock chroot but incredibly slow on bare metal.
I've done a small test of moving files:
[root@cassini icons]# mkdir test
[root@cassini icons]# for (( i = 0; i < 10000; i++ )) do > test/file_$i;
done
[root@cassini icons]# cd test
On host:
time $(for f in *; do mv "$f" "${f%}.txt"; done)
real 2m3,500s
user 0m3,966s
sys 2m0,431s
In nspawn container:
<mock-chroot> sh-5.1# time $(for f in *; do mv "$f" "${f%}.txt"; done)
real 0m6.702s
user 0m4.237s
sys 0m3.344s
Since papirus-icon-theme contains more than 100,000 (small) files, it is
a problem. One minute of waiting is ok, 20 mn is not.
What can cause this? I read that nspawn virtualizes the file system,
could it be file system related on the host? (I use btrfs btw)
Any input welcome!
What file system is being used in each case?
Everything is btrfs.
This is a bit obscure but... cp and mv use reflink=auto. On XFS and
Btrfs this means it'll make reflinks (copies metadata, doesn't
duplicate the data extents) if it can. Falling back to a full copy
(metadata and data extents).
But both the host and the nspawn container are using btrfs?
It might not be possible due to an obscure VFS rule that disallows
reflinks (for reasons I don't understand) when the copy or move
crosses mount point boundaries. This includes bind mounts of
directories. Bind mounts are also what are employed behind the scene
with 'mount -o subvol' mount option on Btrfs, which we use by default
in Fedora Workstation and Cloud Edition, and all the desktop spins.
The nspawn container, I'm not super familiar with how it works. I
think on Btrfs, it will create nested subvolumes, i.e. they are not
mounted with the subvol mount option, hence no mount point boundary.
But on other file systems, I think nspawn creates a loop mounted file
system?
I've got two subvol:
UUID=ee9eec69-8710-4503-b389-e16fcde8a0a5 / btrfs
subvol=root,compress=zstd:1 0 0
UUID=d7e21336-6ac6-483a-b4f2-aaeecabd8f1f /home btrfs
subvol=home,compress=zstd:1 0 0
but when I do my tests there is no subvol crossing, everything happens
on the root subvol?
Thanks for your input.
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