likely similar to Linux memory usage higher than sum of processes except that I have observed used memory going both below and above the sum of process RSS by GBs.
MemTotal: 8155920 kB MemFree: 280200 kB MemAvailable: 328152 kB Buffers: 144 kB Cached: 704380 kB SwapCached: 15440 kB Active: 2374160 kB Inactive: 1195784 kB Active(anon): 2259104 kB Inactive(anon): 1026600 kB Active(file): 115056 kB Inactive(file): 169184 kB Unevictable: 238012 kB Mlocked: 0 kB SwapTotal: 8388604 kB SwapFree: 5908220 kB Dirty: 168 kB Writeback: 0 kB AnonPages: 3097284 kB Mapped: 255492 kB Shmem: 420252 kB KReclaimable: 81636 kB Slab: 346972 kB SReclaimable: 81636 kB SUnreclaim: 265336 kB KernelStack: 14720 kB PageTables: 70776 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 12466564 kB Committed_AS: 9429628 kB VmallocTotal: 34359738367 kB VmallocUsed: 0 kB VmallocChunk: 0 kB Percpu: 2112 kB HardwareCorrupted: 0 kB AnonHugePages: 0 kB ShmemHugePages: 0 kB ShmemPmdMapped: 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: 4764008 kB DirectMap2M: 3614720 kB
the sum of RSS by all processes (summed individually from
top output), slabinfo, buff/cache, swap don't change by more than 100 MBs and yet available memory will increase by GBs after starting ffmpeg... starting ffmpeg on a heavy long term compression task seems to reliably eliminate all disk thrashing and dramatically increase available memory every time (good temp solution, but not acceptable as a long term solution). As ffmpeg runs available memory will drop and the disk will thrash but available memory will then increase by GBs, this behavior remains only so long as ffmpeg is running. If ffmpeg is not running then available memory will go from causing disk thrashing to a few hundred MBs at most. No other program seems to have the same effect for the last ~two months or so of system use. Amusing and annoying.