mjhjmtu

/! Current state: Update 3 /!

Some /proc/meminfo values are a sum or a difference of some other values.
However, not much is said about how they are calculated in these two links (just do ctrl-f meminfo to get there):

• https://www.kernel.org/doc/Documentation/filesystems/proc.txt


• man 5 proc

Besides, I've also dug here and there, and here's what I found so far:

MemFree: LowFree + HighFree
Active: Active(anon) + Active(file)
Inactive: Inactive(anon) + Inactive(file)

I have not found much about the other fields, and where I have, the results don't match, like in these Stack Overflow posts:

• 
  How to Calculate MemTotal in /proc/meminfo
  (2035272 kB vs expected 2034284 kB)


• Entry in /proc/meminfo - on Stack Overflow

Are these two values correctly calculated? Or is there some variability due to some external means?

Also, some values can't -obviously- be calculated without external values, but I'm still interested in that.

How are /proc/meminfo values calculated?

If that helps, here's an example of /proc/meminfo:

MemTotal: 501400 kB
MemFree: 38072 kB
MemAvailable: 217652 kB
Buffers: 0 kB
Cached: 223508 kB
SwapCached: 11200 kB
Active: 179280 kB
Inactive: 181680 kB
Active(anon): 69032 kB
Inactive(anon): 70908 kB
Active(file): 110248 kB
Inactive(file): 110772 kB
Unevictable: 0 kB
Mlocked: 0 kB
HighTotal:
HighFree:
LowTotal:
LowFree:
MmapCopy:
SwapTotal: 839676 kB
SwapFree: 785552 kB
Dirty: 4 kB
Writeback: 0 kB
AnonPages: 128964 kB
Mapped: 21840 kB
Shmem: 2488 kB
Slab: 71940 kB
SReclaimable: 41372 kB
SUnreclaim: 30568 kB
KernelStack: 2736 kB
PageTables: 5196 kB
Quicklists:
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 1090376 kB
Committed_AS: 486916 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 4904 kB
VmallocChunk: 34359721736 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
ShmemHugePages:
ShmemPmdMapped:
CmaTotal:
CmaFree:
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 36800 kB
DirectMap2M: 487424 kB
DirectMap4M:
DirectMap1G:

Update 1:

Here's the code used by /proc/meminfo to fill its data:

http://elixir.free-electrons.com/linux/v4.15/source/fs/proc/meminfo.c#L46

However, since I'm not that of a coder, I'm having a hard time to figure out where these enums (e.g. NR_LRU_LISTS, etc) and global variables (e.g totalram_pages from si_meminfo in page_alloc.c#L4673 ) are filled.

Update 2:

The enums part is now solved, and NR_LRU_LISTS equals 5.

But the totalram_pages part seems to be harder to find out...

Update 3:

It looks like I won't be able to read the code since it looks very complex.
If someone manages to do it and shows how /proc/meminfo valures are calculated, he/she can have the bounty.

The more the answer is detailed is, the higher the higher the bounty will be.

The contents of /proc/meminfo are determined by meminfo_proc_show in fs/proc/meminfo.c in the kernel.

The calculations are all relatively straightforward, but the sources of information used aren’t necessarily so obvious. For example, MemTotal is the totalram value from the sysinfo structure; that’s filled in by si_meminfo in mm/page_alloc.c.