Explain Zram and Swap numbers

Ok, so there are really 2 questions here, why is my on disk swap being used? Is the compression of my swap really this good? It seems pretty unlikely, but it's also possible it is because it's memory that applications (like the JVM) have reserved, but aren't actually using.

Linux manjaro 5.10.59-1-MANJARO #1 SMP PREEMPT Sun Aug 15 13:11:32 UTC 2021 x86_64 GNU/Linux

Here's my initial measurements

❯ swapon
NAME           TYPE       SIZE USED PRIO
/dev/nvme0n1p6 partition 32.2G 2.4G   -2
/dev/zram0     partition    4G 3.5G  100
❯ zramctl
NAME       ALGORITHM DISKSIZE  DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 zstd            4G 42.4M 42.4M 42.4M       8 [SWAP]

❯ cat /proc/meminfo
MemTotal:       16138912 kB
MemFree:          506156 kB
MemAvailable:    1338368 kB
Buffers:              32 kB
Cached:          3733980 kB
SwapCached:      2874732 kB
Active:          6357760 kB
Inactive:        7098592 kB
Active(anon):    5746908 kB
Inactive(anon):  6665988 kB
Active(file):     610852 kB
Inactive(file):   432604 kB
Unevictable:      367084 kB
Mlocked:             224 kB
SwapTotal:      37986296 kB
SwapFree:       31745392 kB
Dirty:              2172 kB
Writeback:             0 kB
AnonPages:       7635524 kB
Mapped:           628752 kB
Shmem:           2692308 kB
KReclaimable:     104768 kB
Slab:             330300 kB
SReclaimable:     104768 kB
SUnreclaim:       225532 kB
KernelStack:       25600 kB
PageTables:        81764 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    46055752 kB
Committed_AS:   24622488 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      110656 kB
VmallocChunk:          0 kB
Percpu:             7552 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
ShmemPmdMapped:        0 kB
FileHugePages:         0 kB
FilePmdMapped:         0 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:               0 kB
DirectMap4k:      813792 kB
DirectMap2M:    15714304 kB
DirectMap1G:           0 kB

❯ free -h
               total        used        free      shared  buff/cache   available
Mem:            15Gi        11Gi       274Mi       2.5Gi       3.9Gi       1.4Gi
Swap:           36Gi       6.0Gi        30Gi

❯ sudo swapoff /dev/nvme0n1p6 After swapoff

❯ zramctl
NAME       ALGORITHM DISKSIZE  DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 zstd            4G 42.9M 42.9M 42.9M       8 [SWAP]
❯ swapon
NAME       TYPE      SIZE USED PRIO
/dev/zram0 partition   4G 3.5G  100

❯ cat /proc/meminfo
MemTotal:       16138912 kB
MemFree:          450240 kB
MemAvailable:    1018456 kB
Buffers:              28 kB
Cached:          3643988 kB
SwapCached:      1249912 kB
Active:          6562884 kB
Inactive:        7350540 kB
Active(anon):    5994940 kB
Inactive(anon):  7018496 kB
Active(file):     567944 kB
Inactive(file):   332044 kB
Unevictable:      168744 kB
Mlocked:             224 kB
SwapTotal:       4194300 kB
SwapFree:         115892 kB
Dirty:               696 kB
Writeback:             0 kB
AnonPages:       9229592 kB
Mapped:           477084 kB
Shmem:           2744240 kB
KReclaimable:     105376 kB
Slab:             326216 kB
SReclaimable:     105376 kB
SUnreclaim:       220840 kB
KernelStack:       26096 kB
PageTables:        83560 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    12263756 kB
Committed_AS:   25151912 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      115640 kB
VmallocChunk:          0 kB
Percpu:             7552 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
ShmemPmdMapped:        0 kB
FileHugePages:         0 kB
FilePmdMapped:         0 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:               0 kB
DirectMap4k:      821984 kB
DirectMap2M:    15706112 kB
DirectMap1G:           0 kB

❯ cat /proc/swaps
Filename				Type		Size		Used		Priority
/dev/zram0                              partition	4194300		4086744		100

❯ free -h
               total        used        free      shared  buff/cache   available
Mem:            15Gi        10Gi       1.0Gi       2.6Gi       4.1Gi       2.1Gi
Swap:          4.0Gi       3.9Gi        97Mi

` So why is zram only 42M? Is that really what it has compressed down to from 3.5G? If that's true, why is my swap partition being used? should't all of it be in zram?