Estimating total memory usage in any Linux system

Estimating total memory usage in any Linux system

[Pintu Agarwal]

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:

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

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Re: Estimating total memory usage in any Linux system

[Pintu Agarwal]

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

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Re: Estimating total memory usage in any Linux system

[Valdis Klētnieks]

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On Tue, 19 May 2020 22:33:15 +0530, Pintu Agarwal said:

> > 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

That's a kernel from 2014.  You don't seriously expect us to remember how
all those counters worked back then, do you?

That's a very real issue, not sarcasm:

[/usr/src/linux-next] git diff --shortstat v3.18..next-20200518
 76288 files changed, 15101441 insertions(+), 5417984 deletions(-)

You're asking about what the numbers meant 15 million lines of code ago.

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Re: Estimating total memory usage in any Linux system

[Pintu Agarwal]

On Wed, 20 May 2020 at 09:31, Valdis Klētnieks <valdis.kletnieks@vt.edu> wrote:
>
> On Tue, 19 May 2020 22:33:15 +0530, Pintu Agarwal said:
>
> > > 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
>
> That's a kernel from 2014.  You don't seriously expect us to remember how
> all those counters worked back then, do you?
>
Actually I don't care about the kernel version. This was just for reference.
I know it is weird to manually arrive a MemTotal from the values of meminfo.
But I am actually looking for general formula.
I could get some of the answers by tracing the kernel code for each counters.
But still there are some gaps which I want to clarify.
As I see there are several ways to total it: i.e; (PSS way), (Buffers,
Cached), (Active, Inactive)
According to me,
MemTotal = MemFree + Active + Inactive  + SwapCached + Mapped + Shmem
+ Slab + KernelStack + PageTables + (Init Freed from boot) + (alloc
pages) + (min_free_bytes + user_reserve_bytes)
Did I miss anything here ?

With this I could arrive to some result, but I have some doubts:
* Is Mapped already included in Active/Inactive (file) ? Because
mapped is coming from NR_FILE_MAPPED.
  ==> I see that it is accounted from mm/rmap.c
* Do we also need to incude VmallocUsed here ? I see in some cases
people include it too.
  ==> But I think vmalloc internally calls kmalloc and use page
tables, so it should be already accounted in Slab and PageTables ??
  ==> Do I still need to include these values from /proc/vmallocinfo ??
* Is it valid to include min_free_kbytes and user_reserve_kbytes here
? Its kind of reserve for internal purpose but still it contributes to
the total.
* Is kernel internal allocation (alloc_pages) statistics accounted somewhere ?
  ==> I can see that some counters like (pgalloc_normal, etc. and
pgfree) are available as part of /proc/vmstat
  ===> But this is like overall allocation and free stats.
* Apart from these, do we also need to consider Graphics/3D allocation
separately ?


Thanks,
Pintu

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Re: Estimating total memory usage in any Linux system

[Valdis Klētnieks]

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On Wed, 20 May 2020 10:26:50 +0530, Pintu Agarwal said:
> I know it is weird to manually arrive a MemTotal from the values of meminfo.
> But I am actually looking for general formula.

You missed the point - the "general formula" has probably changed over the years.

> With this I could arrive to some result, but I have some doubts:
> * Is Mapped already included in Active/Inactive (file) ? Because
> mapped is coming from NR_FILE_MAPPED.

And that's the sort of question that can have different answers for 3.18 and 5.7.



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Re: Estimating total memory usage in any Linux system

[Pintu Agarwal]

On Wed, 20 May 2020 at 11:02, Valdis Klētnieks <valdis.kletnieks@vt.edu> wrote:
>
> On Wed, 20 May 2020 10:26:50 +0530, Pintu Agarwal said:
> > I know it is weird to manually arrive a MemTotal from the values of meminfo.
> > But I am actually looking for general formula.
>
> You missed the point - the "general formula" has probably changed over the years.
>
> > With this I could arrive to some result, but I have some doubts:
> > * Is Mapped already included in Active/Inactive (file) ? Because
> > mapped is coming from NR_FILE_MAPPED.
>
> And that's the sort of question that can have different answers for 3.18 and 5.7.
>
I am okay for even the latest kernel. I am even trying to get this on
5.5 kernel or higher.
But my questions remains the same.
What will be the equation for even 5.7 kerne ?

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