Tracing large binary allocations

[Vans S]

 So you need to refernce the old docs, http://erlang.org/documentation/doc-9.3/lib/tools-2.11.2/doc/html/instrument.html.

memory_data() will return a list of all the allocations, find the binary heap in there and itl show which memory address the terms are stored at.  You can then check the processes memory /proc/#{:os.pid()}/mem at that address for the actual term.

Also a few useful hipe bifs as well that got removed also https://github.com/erlang/otp/blob/master/erts/emulator/hipe/hipe_bif2.tab





    On Thursday, April 9, 2020, 08:43:49 a.m. EDT, Frank Muller <frank.muller.erl@REDACTED> wrote:  
 
 Vans,
Can you please share how to track these large binaries with let’s say Erlang 20 and/or HIPE?
This will be useful to all of us and Devon can certainly downgrade to Erlang 20 to at least identify the culprit. 
/Frank


 This used to be possible via the instrument module but the functionality got removed in OTP21, I used this functionality to detect a large binheap leak in jiffy way back when. Theres a lengthy discussion here under a PR called "improve instrumentation" but it really just "removed instrumentation" https://github.com/erlang/otp/pull/1790.

There are BIF debug functions under hipe that can print this information.  hipe_bifs:show_heap/1 and friends.    On Wednesday, April 8, 2020, 02:53:49 p.m. EDT, Dániel Szoboszlay <dszoboszlay@REDACTED> wrote:  
 
 Hi,
Even though you cannot trace on allocating large binaries, you may try tracing garbage collections, and look for GC-s that clean up a lot of off-heap binary data. This could at least narrow done the search for some processes, although it won't tell you where the allocation happens. But maybe once you know which processes are guilty you will be able to add more targeted tracing until you find the root cause.
Cheers,Daniel
On Wed, 8 Apr 2020 at 16:14, Lukas Larsson <lukas@REDACTED> wrote:

Hello,
On Tue, Apr 7, 2020 at 9:26 AM Devon Estes <devon.c.estes@REDACTED> wrote:

Hi all,
I’m seeing some cases in my application where our off-process binary heap allocation jumps by several orders of magnitude and then goes down right after. I’m sure this is something that’s in our app just loading dozens of huge binaries into memory at once and not a bug in anything underlying or a binary leak, but finding where these allocations are happening so I can make some changes to avoid this has so far not yielded any results. Ideally I’d like to be able to set a trace with something like erlang:trace/3 on some function that sends a tracer message whenever a binary over 30MB is allocated and includes the call stack or even just the calling function that allocated the binary in the trace message. 


Going through the binary vheap and getting a list of the processes that have references to those binaries won’t help in this case.
Is such a trace possible? Is there some flag I can set when starting my BEAM process to give me some kind of debug output that would give me this information? I’d imagine this is all in C, so it might be a bit tricky...

No it is not possible without modifying the VM. I can't think of any good way to get this information without scanning the process' vheap, which as you say would not help much in this case.


Thanks in advance for the help!
Cheers,Devon-- 

_________________
Devon Estes
203.559.0323
www.devonestes.com



  
  
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