apply different compress/compress-force settings on different subvolumes ?

[Roland <devzero@web.de>]

hello,

what can be the reason , that multiple compress mount option do not work
on subvolume level , i.e. it's always the first that wins ?

and why is compress-force silently ignored? (see below)

regarding compress mount option, it seems that this can be overriden via
subvolume property, which can work around the problem and have multiple
compression settings.

but how to fix compress-force in the same way, i.e. how can we have
differenty compress-force settings with one btrfs fs ?

wouldn't it make sense to introduce compress-force property for this ?

what about replacing compress with compress-force (i.e. make it the
default), as there is not much overhead with modern/fast cpu ?

i think compress-force / compress is VERY confusing from and end user
perspective - and even worse, i have set "compress" on a subvolume used
for virtual machines and they do not get compressed at all (not a single
bit) . so i think, compress option is pretty short-sighted and not, what
an average user would expect (
https://marc.info/?l=linux-btrfs&m=154523409314147&w=2 )

i'd be happy on some feedback. not subscribed to this list, so please CC.

roland


zstd compression applied to all subvolumes, though specified otherwise:

cat /etc/fstab|grep btrfs
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/zstd btrfs
subvol=zstd,compress=zstd,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/lzo  btrfs
subvol=lzo,compress=lzo,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/none btrfs
subvol=none,compress=none,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/zstd-force btrfs
subvol=zstd-force,compress-force=zstd,defaults 0 1

mount|grep btrfs
/dev/sdb1 on /btrfs/zstd type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=259,subvol=/zstd)
/dev/sdb1 on /btrfs/lzo type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=257,subvol=/lzo)
/dev/sdb1 on /btrfs/none type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=258,subvol=/none)
/dev/sdb1 on /btrfs/zstd-force type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=260,subvol=/zstd-force)


different order in fstab has different result - first wins:

UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/lzo  btrfs
subvol=lzo,compress=lzo,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/zstd btrfs
subvol=zstd,compress=zstd,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/none btrfs
subvol=none,compress=none,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/zstd-force btrfs
subvol=zstd-force,compress-force=zstd,defaults 0 1

/dev/sdb1 on /btrfs/lzo type btrfs
(rw,relatime,compress=lzo,ssd,discard=async,space_cache=v2,subvolid=257,subvol=/lzo)
/dev/sdb1 on /btrfs/zstd type btrfs
(rw,relatime,compress=lzo,ssd,discard=async,space_cache=v2,subvolid=259,subvol=/zstd)
/dev/sdb1 on /btrfs/none type btrfs
(rw,relatime,compress=lzo,ssd,discard=async,space_cache=v2,subvolid=258,subvol=/none)
/dev/sdb1 on /btrfs/zstd-force type btrfs
(rw,relatime,compress=lzo,ssd,discard=async,space_cache=v2,subvolid=260,subvol=/zstd-force)


compress-force silently ignored:

UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/zstd btrfs
subvol=zstd,compress=zstd,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/lzo  btrfs
subvol=lzo,compress=lzo,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/none btrfs
subvol=none,compress=none,defaults 0 1
UUID=da0fadf1-5db4-4f5b-a77e-2f0730f4e872 /btrfs/zstd-force btrfs
subvol=zstd-force,compress-force=zstd,defaults 0 1

/dev/sdb1 on /btrfs/zstd type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=259,subvol=/zstd)
/dev/sdb1 on /btrfs/lzo type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=257,subvol=/lzo)
/dev/sdb1 on /btrfs/none type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=258,subvol=/none)
/dev/sdb1 on /btrfs/zstd-force type btrfs
(rw,relatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=260,subvol=/zstd-force)



this is the write speed i get with compress-force=zstd on i7-7700

# dd if=/dev/zero of=test.dat bs=1024k count=10240 ;time sync
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB, 10 GiB) copied, 3.76111 s, 2.9 GB/s

real    0m0.224s
user    0m0.000s
sys    0m0.081s