# Memory usage discrepancy

**URL:** <https://discourse.julialang.org/t/memory-usage-discrepancy/126085>\
**Category:** General Usage\
**Tags:** question, memory\
**Created:** [February 19, 2025, 5:20pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085 "2025-02-19T17:20:21Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![ohmsweetohm1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ohmsweetohm1/32/49126_2.png) [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Post date:** [February 19, 2025, 5:20pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/1 "2025-02-19T17:20:21Z")

</div>

I have an application running in Julia.

Using `htop` I can see that the process consumes 2 GB of memory, but if I use `summarysize` of all symbols in Main I just get around 150 MB in total. How can this be?

I’m using Julia v1.11.2

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<div class="post-metadata">

**Author:** ![baggepinnen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/baggepinnen/32/693_2.png) [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)\
**Post date:** [February 19, 2025, 5:27pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/2 "2025-02-19T17:27:19Z")

</div>

I have also found `summarysize` to be of little use trying to find out where memory is stashed. I was once pointed to this snippet by @gbaraldi

```julia
function take_heap_snapshot(filename::String)
    flags = Base.open_flags(
        read = true,
        write = true,
        create = true,
        truncate = true,
        append = false,
    )
    nodes = IOStream("<file $filename.nodes>")
    ccall(:ios_file, Ptr{Cvoid}, (Ptr{UInt8}, Cstring, Cint, Cint, Cint, Cint),
        nodes.ios, "$filename.nodes", flags.read, flags.write, flags.create, flags.truncate)
    edges = IOStream("<file $filename.edges>")
    ccall(:ios_file, Ptr{Cvoid}, (Ptr{UInt8}, Cstring, Cint, Cint, Cint, Cint),
        edges.ios, "$filename.edges", flags.read, flags.write, flags.create, flags.truncate)
    strings = IOStream("<file $filename.strings>")
    ccall(:ios_file, Ptr{Cvoid},(Ptr{UInt8}, Cstring, Cint, Cint, Cint, Cint),
        strings.ios, "$filename.strings", flags.read, flags.write, flags.create, flags.truncate)
    json = IOStream("<file $filename.metadata.json>")
    ccall(:ios_file, Ptr{Cvoid}, (Ptr{UInt8}, Cstring, Cint, Cint, Cint, Cint),
        json.ios, "$filename.metadata.json", flags.read, flags.write, flags.create, flags.truncate)
    ccall(:jl_gc_take_heap_snapshot,
        Cvoid,
        (Ptr{Cvoid},Ptr{Cvoid},Ptr{Cvoid},Ptr{Cvoid}, Cchar),
        nodes.handle, edges.handle, strings.handle, json.handle,
        Cchar(false))
    ccall(:ios_close, Cint, (Ptr{Cvoid},), nodes.ios)
    ccall(:ios_close, Cint, (Ptr{Cvoid},), edges.ios)
    ccall(:ios_close, Cint, (Ptr{Cvoid},), strings.ios)
    ccall(:ios_close, Cint, (Ptr{Cvoid},), json.ios)
    return nothing
end

```

if you call this function somewhere and then call

```julia
Profile.Heapsnapshot.assemble

```

with the first argument to assemble is the prefix you passed in to `take_heap_snapshot`, and the second is `<filename>.heapsnapshot`, like this

```julia
 Profile.HeapSnapshot.assemble_snapshot("heap_snapshot", "heap_snapshot.heapsnapshot")

```

You should be able to look at the heap snapshot in vscode or in chrome by pressing F12, go to memory and heap snapshot

Thanks to @gbaraldi for those instructions, I mostly copied them from him, and he might be able to provide further insights if you get stuck or have quesitons I cannot answer.

---

<div class="post-metadata">

**Author:** ![Benny](https://avatars.discourse-cdn.com/v4/letter/b/49beb7/32.png) [@Benny](https://discourse.julialang.org/u/Benny)\
**Post date:** [February 19, 2025, 5:43pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/3 "2025-02-19T17:43:27Z")

</div>

1. Names in `Main` don’t account for every symbol in a Julia process, there are other modules.

2. There are many relevant things to an object that `Base.summarysize` doesn’t count; note that the docstring for `summarysize` says “all unique objects reachable”. Think of a function: it has a type, multiple methods, each method can have several compiled versions, the compiler itself must also take up memory. But those are known to be shared by every instance of the function, so `summarysize` will be much lower, often `0`.

3. I’m not sure if you’re doing this, but adding up results of `summarysize` called for each symbol separately would overcount reached unique objects. Given `x = collect(1:1000); y = view(x, :)`, we know most of the memory is contributed by `x`, and `y` adds very little. However, `Base.summarysize(x) + Base.summarysize(y)` counts `x`’s memory twice, whereas `Base.summarysize((x,y))` does not.

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<div class="post-metadata">

**Author:** ![gbaraldi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gbaraldi/32/22101_2.png) [@gbaraldi](https://discourse.julialang.org/u/gbaraldi)\
**Post date:** [February 19, 2025, 7:14pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/4 "2025-02-19T19:14:25Z")

</div>

You needn’t use this version of this code. This was just for --trim.  
`Profile.take_heap_snapshot` does the same thing but easier/nicer

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<div class="post-metadata">

**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [February 19, 2025, 7:59pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/5 "2025-02-19T19:59:11Z")

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For `htop` are you looking at virtual or resident memory? Julia is fairly careless with virtual memory since it tends to be almost completely free (since unix systems won’t actually give you the pages until you ask for them).

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<div class="post-metadata">

**Author:** ![ohmsweetohm1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ohmsweetohm1/32/49126_2.png) [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Post date:** [February 19, 2025, 8:13pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/6 "2025-02-19T20:13:59Z")

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I took a heap snapshot. It is 620 MB large. But to be honest, I cannot do much with it.

 ![image](https://global.discourse-cdn.com/julialang/original/3X/a/9/a95dbcde9e7fe0e41468a0fecf67cff47894bfab.png)

If I start Julia and activate my environment, it is 230 MB.

If I compare the two I see this:

 ![image](https://global.discourse-cdn.com/julialang/original/3X/f/9/f99f9fdd4d501137b223cb80e1fe8a701ddf0f0a.png)

Is `(String)` my Code that is loaded?

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<div class="post-metadata">

**Author:** ![ohmsweetohm1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ohmsweetohm1/32/49126_2.png) [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Post date:** [February 19, 2025, 8:31pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/7 "2025-02-19T20:31:03Z")

</div>

I definitely have a memory leak somewhere. This is a Grafana screenshot. I added logging of my `summarysize` approach (which is entirely wrong) and what I get in total RSS with `ps`.

 ![image](https://global.discourse-cdn.com/julialang/original/3X/3/f/3fc559bc6e6a3c7443d6e295d0b001a12b4a2f17.png)

My app uses HiGHS.jl, which might be the source. Since JuMP.jl creates the optimizer on the fly, it needs to be destroyed as well: [HiGHS.jl/src/MOI\_wrapper.jl at 577ecc26040fb2a8186cd51f4850c8c41c21c98a · jump-dev/HiGHS.jl · GitHub](https://github.com/jump-dev/HiGHS.jl/blob/577ecc26040fb2a8186cd51f4850c8c41c21c98a/src/MOI_wrapper.jl#L326)

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<div class="post-metadata">

**Author:** ![ohmsweetohm1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ohmsweetohm1/32/49126_2.png) [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Post date:** [February 20, 2025, 8:32am UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/8 "2025-02-20T08:32:27Z")

</div>

Letting it run overnight I see that the memory usage flattens out:

 ![image](https://global.discourse-cdn.com/julialang/original/3X/b/e/be419fdfbb652adc8c786ea9a4467e68950b9089.png)

I would guess that there is some problem with the GC. I will try with `--heap-size-hint`.

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<div class="post-metadata">

**Author:** ![ohmsweetohm1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ohmsweetohm1/32/49126_2.png) [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Post date:** [February 20, 2025, 5:06pm UTC](https://discourse.julialang.org/t/memory-usage-discrepancy/126085/9 "2025-02-20T17:06:58Z")

</div>

Running with `--heap-size-hint=1G` and a `GC.gc()` after the optimization takes place solved the issue. It is now a steady 1.7 GB.