I have that server running kernel 4.18, where some memory seems to have gone missing in action - with the common culprits (kernel slab memory, page cache) already ruled out.
Some 6 GB are being used (MemTotal - MemAvailable), but if I add up what is used by processes, kernel slab and shmem, that barely gets me to 1 GB. That is right after a cold boot. Where might the other 5 have gone?
Strangest thing is, I have an identical server running the exact same applications, and MemAvailable is, in fact, 5 GB higher there.
# ps fauxw | sed 1d | awk '{ x += $6 } END { print x }' 757368 # cat /proc/meminfo MemTotal: 32826040 kB MemFree: 26493788 kB MemAvailable: 26322932 kB Buffers: 11948 kB Cached: 72584 kB SwapCached: 0 kB Active: 247756 kB Inactive: 41348 kB Active(anon): 204952 kB Inactive(anon): 1012 kB Active(file): 42804 kB Inactive(file): 40336 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 4 kB Writeback: 0 kB AnonPages: 204632 kB Mapped: 33052 kB Shmem: 1396 kB Slab: 219376 kB SReclaimable: 30744 kB SUnreclaim: 188632 kB KernelStack: 18960 kB PageTables: 12548 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 16413020 kB Committed_AS: 4565744 kB VmallocTotal: 34359738367 kB VmallocUsed: 0 kB VmallocChunk: 0 kB HardwareCorrupted: 0 kB AnonHugePages: 0 kB ShmemHugePages: 0 kB ShmemPmdMapped: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 186396 kB DirectMap2M: 9152512 kB DirectMap1G: 26214400 kB 