Checks on virtual_memory() and swap_memory() values

[dmedri]

On Linux (fedora23, i686), running psutil.cpu_memory() and free (on Py3), the results are wrong:

>>> psutil.virtual_memory()
svmem(total=2103410688, available=1315647488, percent=37.5, used=2044448768,
free=58961920, active=958812160, inactive=962322432, buffers=77824, cached=1256607744)

>>> psutil.swap_memory()
sswap(total=2148528128, used=48975872, free=2099552256, percent=2.3, sin=49152,
sout=48984064)

in console, results are differents:

> free
              total        used        free      shared  buff/cache   available
Mem:        2054112      682720       55752      190224     1315640     1132484
Swap:       2098172       47828     2050344

Let me know how can I run some tests to help you.

[giampaolo]

Some values of free and psutil.virtual_memory() refer to different things and cannot be compared.
E.g. used and available are calculated differently.
Secondly, psutil returns results in bytes. In order for free to do the same you should do free -b.

[dmedri]

Ok, second try:

>>> psutil.virtual_memory()
svmem(total=2103410688, available=1310154752, percent=37.7, used=2012487680,
free=90923008, active=908922880, inactive=971247616, buffers=28672, cached=1219203072)

>>> psutil.swap_memory()
sswap(total=2148528128, used=38989824, free=2109538304, percent=1.8, sin=217088,
sout=39026688)

and free -b results:

$ free -b
              total        used        free      shared  buff/cache   available
Mem:     2103410688   703737856    76132352   182116352  1323540480  1166770176
Swap:    2148528128    38989824  2109538304

Please, sync your method with the 'free' developers for a final resolution.

[giampaolo]

Update about this: I updated Linux tests and with Ubuntu 16.04 free column of "free" cmdline utility matches psutil. I suspect there are "free" versions where this is different, see:
#685 (comment)
Anyway, I checked the output of vmstat -s and the two values (vmstat and psutil) matches so I think "free" value is fine.

What is not fine is "used" value.
Both vmstat and free CLI tools report different numbers but I'm not sure how they calculate that. I'll have to take a peek at the source code.

[giampaolo]

Fixed in #887