好的，这里确实有两个问题，为什么我的磁盘交换被使用？我的交换区的压缩真的这么好吗？这看起来不太可能，但也有可能是因为应用程序（如 JVM）保留了内存，但实际上并未使用它。
Linux manjaro 5.10.59-1-MANJARO #1 SMP PREEMPT Sun Aug 15 13:11:32 UTC 2021 x86_64 GNU/Linux
这是我的初步测量结果
❯ 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]
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
后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
那么为什么zram只有42M呢？这真的是从3.5G压缩到的吗？如果这是真的，为什么我的交换分区被使用？不应该全部都在吗zram？
答案1
您的内核可能正在使用 zswap。从www.kernel.org:
Zswap 是一个轻量级的交换页压缩缓存。它获取正在换出的页面并尝试将它们压缩到动态分配的基于 RAM 的内存池中。
约 3.5GB 的数据已被“交换”，但位于压缩的 zswap 池中，并且尚未被逐出到后备交换设备 (zram)，因此从zramctl.
您可以通过禁用 zswap 并通过删除并重新添加 zram 交换设备强制其清空池来确认这一点：
# echo 0 > /sys/module/zswap/parameters/enabled
# swapoff /dev/zram0
# swapon /dev/zram0