Discrepancy between OS memory and erlang virtual memory?

Dominic Letz dominic@REDACTED
Thu Sep 23 13:30:45 CEST 2021

Great that it helped! Yes I went for OTP 24. If you don't want to switch
yet you can also so just disable the affected Erlang VM carrier.

E.g. to disable the binary alloc carrier add `+MBe false` to your erlang
start args.


Hitesh Kishorbhai Vaghani <hitesh.v@REDACTED> schrieb am Do., 23. Sep.
2021, 10:23:

> Dominic, Thanks for your scripts . It has helped to identify issues
> with {binary_alloc,3140268032}, All the missing memory is allocated into
> binary_alloc.
> We do using binary_to_term on 1 to 4 MB blob variables. Which version of
> OTP have you migrated to? We are also planning to migrate OTP21 to OTP24.
> Roger,
> We are not using NIFs. We using heavy concurrent processing to reduce
> response time. how to check the default allocator?
> *Regards,*
> *Hitesh Vaghani*
> On Thu, Sep 23, 2021 at 1:06 PM Roger Lipscombe <roger@REDACTED>
> wrote:
>> Yes, recon has useful functions for reporting on fragmentation.
>> Question: are you doing anything with NIFs? We had a problem a few
>> years ago where the default glibc allocator in Ubuntu 14/16, when used
>> in a heavily multi-threaded way (i.e. when being called from Erlang),
>> caused a *lot* of fragmentation, and it's hard to track down.
>> Switching to a more modern allocator (we chose jemalloc) basically
>> resolved the problem immediately.
>> On Thu, 23 Sept 2021 at 08:13, Dominic Letz <dominic@REDACTED> wrote:
>> >
>> > The erlang vm has it's own memory allocators (carriers) they usually
>> create a small memory overhead. I've seen them consuming exorbitant amounts
>> of memory before, likely because of memory fragmentation. Their usage is
>> not reported in the erlang virtual memory stats by default but you can
>> check them explicitly.
>> >
>> > When fighting with memory fragmentation I created this script to show
>> the current carrier overhead: (waste)
>> https://gist.github.com/dominicletz/615e4b89b9e6f2059b2520ed9adac5dc
>> >
>> > My solution in the end was to upgrade OTP to a newer version. And it
>> made the crazy overheads go away.
>> >
>> >  Cheers!
>> >
>> > Max Lapshin <max.lapshin@REDACTED> schrieb am Do., 23. Sep. 2021,
>> 08:42:
>> >>
>> >> You show a strange graphic without any numbers. all other commands are
>> also cutted.
>> >>
>> >> Also part of your email is rather unclear: you write to a public list
>> that your email is confidential. Bad idea.
>> >>
>> >> About memory:
>> >>
>> >> 1) use recon in your production. recon_alloc will help to collect big
>> amount of information from erlang runtime
>> >> 2) take a look at /proc/3975367/maps, sometimes it helps to find leaks
>> or better interpret numbers.
>> >>
>> >> What you see is a mismatch between different ways to calculate memory.
>> Usually it is ok to live with such a difference.
>> >>
>> >>
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