Linux Free Shows High Memory Usage But Top Does Not

Linux free shows high memory usage but top does not

Don't look at the "Mem" line, look at the one below it.

The Linux kernel consumes as much memory as it can to provide the I/O cache (and other non-critical buffers, but the cache is going to be most of this usage). This memory is relinquished to processes when they request it. The "-/+ buffers/cache" line is showing you the adjusted values after the I/O cache is accounted for, that is, the amount of memory used by processes and the amount available to processes (in this case, 578MB used and 7411MB free).

The difference of used memory between the "Mem" and "-/+ buffers/cache" line shows you how much is in use by the kernel for the purposes of caching: 7734MB - 578MB = 7156MB in the I/O cache. If processes need this memory, the kernel will simply shrink the size of the I/O cache.

Why do 'htop' and 'top' show different memory usage?

Top counts the cache aswell.

So if you do:

X = Used

Y = Buffers

Z = Cached

X - Y - Z = HTOPMEM

Memory used but i can't see process that used it (Debian)

www.linuxatemyram.com

It's too good of a site to ruin by copy/pasting the entire contents here.

Linux free -m : Total, used and free memory values don't add up

For the main memory, the actual size of memory can be calculated as used+free+buffers+cache OR used+free+buffers/cache because buffers/cache = buffer+cache.

The man page of free highlights used as Used memory (calculated as total - free - buffers - cache)

As the man page of free says :-

total Total installed memory (MemTotal and SwapTotal in /proc/meminfo)

used Used memory (calculated as total - free - buffers - cache)

free Unused memory (MemFree and SwapFree in /proc/meminfo)

shared Memory used (mostly) by tmpfs (Shmem in /proc/meminfo,
on kernels 2.6.32, displayed as zero if not available)

buffers 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 cache

available 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 reclaimed due to items being in use (MemAvailable in /proc/meminfo, available on kernels 3.14, emulated on kernels 2.6.27+, otherwise the same as free)

In your case,

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873224(used) + 389320(free) + 25493068(buff/cache) = 26755612(total)

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Why would free be reporting a freakishly high swap used value?

Are the systems running kernel-2.6.32-573.1.1.el6.x86_64?

Could be this bug:
access.redhat.com/solutions/1571043

Memory usage doesn't decrease when free() used

On many operating systems, free() doesn't make the memory available for the OS again, but "only" for new calls to malloc(). This is why you don't see the memory usage go down externally, but when you increase the number of new allocations by threading, the memory is re-used so total usage doesn't go through the roof.

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