Here's the output of free -m:              total        used        free      shared  buff/cache   availableMem:            421         158         153          39         109         195Swap:             0           0           0I executed echo 3 > /proc/sys/vm/drop_caches to drop all possible caches, but buff/cache value still stays at 109MB. What holds those caches? Can I drop them somehow?System used is XUbuntu 16.04.Some of those caches (43mb) are probably used by tmpfs:tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=43188k,mode=700,uid=1000,gid=1000)Which leaves more space to account for.Output of df -mt tmpfs:Filesystem     1M-blocks  Used Available Use% Mounted ontmpfs                 43     3        40   7% /runtmpfs                211     1       211   1% /dev/shmtmpfs                  5     1         5   1% /run/locktmpfs                211     0       211   0% /sys/fs/cgrouptmpfs                 43     1        43   1% /run/user/1000
Why are some caches not droppable?
linux;memory;cache
$ man freebuffers            Memory used by kernel buffers (Buffers in /proc/meminfo)cache  Memory  used  by  the  page  cache and slabs (Cached and  Slab in            /proc/meminfo)buff/cache            Sum of buffers and cacheavailable            Estimation of how much memory  is  available  for  starting  new            applications,  without swapping. Unlike the data provided by the            cache or free fields, this field takes into account  page  cache            and also that not all reclaimable memory slabs will be reclaimeddue to items being in use (MemAvailable in /proc/meminfo, avail            able on kernels 3.14, emulated on kernels 2.6.27+, otherwise the            same as free)So there's no wonder buff/cache does not fall to near-0.  The real puzzle is that available does not account for the full total of free and buff/cache.  The mystery memory gap is about 65MB.    (Not sure if tmpfs allocations are reflected sensibly here; again, that should be trivial to test).  I don't know whether the Estimation is expected to break down at this point.