On Mon, 18 May 2020 at 23:27, Pintu Agarwal <pintu.ping@gmail.com> wrote:
Hi,
I was just trying to manually calculate the total memory available in a system to match up the MemTotal shown in /proc/meminfo I know "free -m" command will give the vary high level usage, but I wanted to breakdown the MemTotal numbers to see usage in each category.
I am looking for a common formula that should match on almost all systems. So, I came up with below fields from meminfo to closely match the total. ~Total = {MemFree + Active + Inactive + Shmem + Mapped + Slab + KernelStack + PageTables + (init freed) + (Boot Diff) + (low watermarks)}
But I am not sure if these fields are correct at least for arm32 system. In some boards I could able to match up these figures, but some not.
So I have some doubts: * Is "Mapped" (NR_MAPPED_PAGES) already part of Active pages ? * Is Kernel allocation (alloc_pages, etc.) accounted somewhere ? Is it part of Anon pages ? * What about vmalloc / ioremap pages ? Do we also need to consider VmallocUsed ? ==> In my opinion vmalloc internally used kmalloc and page tables, so I guess it should be already part of Slab or PageTables ??
Below are some data taken from a small embedded arm32 device with 512MB RAM:
Sorry, I forgot to mention the kernel version. Here it is 3.18 Kernel
Kernel Boot Logs: Memory: 99244K/254976K available (10720K kernel code, 1336K rwdata, 4792K rodata, 400K init, 1602K bss, 135252K reserved, 20480K cma-reserved) Total = 99244 + 400 (init) + 20480 (cma) = 120124 Boot Diff = 121204 - 120124 => 1080 kB
MemTotal: 121204 kB MemFree: 2540 kB MemAvailable: 51924 kB Buffers: 0 kB Cached: 47492 kB SwapCached: 0 kB Active: 42604 kB Inactive: 24308 kB Active(anon): 19476 kB Inactive(anon): 92 kB Active(file): 23128 kB Inactive(file): 24216 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 8 kB Writeback: 0 kB AnonPages: 19452 kB Mapped: 12644 kB Shmem: 148 kB Slab: 27560 kB SReclaimable: 7224 kB SUnreclaim: 20336 kB KernelStack: 3104 kB PageTables: 1896 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 60600 kB Committed_AS: 1576740 kB VmallocTotal: 777216 kB VmallocUsed: 53696 kB VmallocChunk: 689148 kB --------------------
These are my calculations from the above fields. --------------------- MemFree 2540 Active 42604 Inactive 24308 Mapped 12644 Slab 27560 KernelStack 3104 PageTables 1896 Shmem 148 init freed 400 Diff from boot total 1080 min_free_kbytes 1384 user_reserve_kbytes 3537 My Total ==> 121205 (add all the above)
As you can see "My Total" closely matches with the MemTotal from /proc/meminfo
But on some systems it does not match. So, I wanted to understand if there is something wrong in my calculation, or there is something wrong in the system itself (like leaks etc,)
Note: I don't want to use any tools or utilize for these, but I wanted to manually understand it.
I am also trying to explore every vm counter that populates these fields.
But if you have any other opinion about it please let me know.
Thanks, Pintu