<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Thanks for taking a look.<div class=""><br class=""></div><div class="">Please note that I'm not looking for a memory leak here: The objects are short-living (within the scope of a method) and no two instances exist at the same time, hence no increase in heap size.<br class=""><div class=""><br class=""></div><div class="">Instead, what got me wondering was the mismatch between the amount of memory allocated for a rather small number of objects (740 MiB for 141 DirectByteBuffers). At least the record only contains these 72 allocations via `ByteBuffer.duplicate()` + 69 `NativeMemorySegmentImpl.makeByteBuffer()`. I'm looking at this chart: <a href="https://static.cryptomator.org/tmp/before890035c.png" class="">https://static.cryptomator.org/tmp/before890035c.png</a></div><div class=""><br class=""></div><div class="">I have very limited experience with JFR and JMC and don't know if it is profiling of sampling allocations. But maybe the events are incomplete and I'm in fact dealing with thousands of instances?</div><div class=""><br class=""></div><div class=""><div class=""><br class=""></div><div class=""><div><blockquote type="cite" class=""><div class="">On 26. Oct 2022, at 10:53, Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" class="">maurizio.cimadamore@oracle.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div class=""><p class="">Looking at this recordings with JMC is inconclusive.</p><p class="">All I see is that your app seems to be using up to 20MB heap,
which seems rather low.</p><p class="">The number of live objects, at least according to the tool is a
handful (< 10).</p><p class="">I don't see anything here indicating a problem? (but maybe I'm
looking in the wrong place?)<br class="">
</p><p class="">Maurizio<br class="">
</p>
<div class="moz-cite-prefix">On 25/10/2022 15:15, Sebastian Stenzel
wrote:<br class="">
</div>
<blockquote type="cite" cite="mid:D73370F0-A6BB-4844-A7B2-87D3F9516586@gmail.com" class="">
Ok so here are the recordings:
<div class=""><br class="">
</div>
<div class="">with duplicate(): <a href="https://urldefense.com/v3/__https://static.cryptomator.org/tmp/before890035c.jfr__;!!ACWV5N9M2RV99hQ!JDzHI5oiHSZJaLRKXbpqU6kqSKHSD0yZEIW8lQT4wRJq0M-_iS6Kz59xcSpcX_sMupZlUpzmv9uLpTNulFGUEIRVe93lmH_Uzw$" class="" moz-do-not-send="true">https://static.cryptomator.org/tmp/before890035c.jfr</a></div>
<div class="">without: <a href="https://urldefense.com/v3/__https://static.cryptomator.org/tmp/after890035c.jfr__;!!ACWV5N9M2RV99hQ!JDzHI5oiHSZJaLRKXbpqU6kqSKHSD0yZEIW8lQT4wRJq0M-_iS6Kz59xcSpcX_sMupZlUpzmv9uLpTNulFGUEIRVe93JaaOc7g$" class="" moz-do-not-send="true">https://static.cryptomator.org/tmp/after890035c.jfr</a></div>
<div class=""><br class="">
</div>
<div class="">This is the diff in code: <a href="https://urldefense.com/v3/__https://github.com/cryptomator/jfuse/commit/890035c702489cdb2e094a1fc767e75b15b04891__;!!ACWV5N9M2RV99hQ!JDzHI5oiHSZJaLRKXbpqU6kqSKHSD0yZEIW8lQT4wRJq0M-_iS6Kz59xcSpcX_sMupZlUpzmv9uLpTNulFGUEIRVe92yJr55Hg$" class="" moz-do-not-send="true">https://github.com/cryptomator/jfuse/commit/890035c702489cdb2e094a1fc767e75b15b04891</a></div>
<div class=""><br class="">
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<div class="">I was testing the `read` method in this class.
`write` (with its `.asReadOnlyBuffer()`) did not draw my
attention.</div>
<div class="">
<div class="">
<div class="">
<div class=""><br class="">
<blockquote type="cite" class="">
<div class="">On 25. Oct 2022, at 15:03, Maurizio
Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" class="moz-txt-link-freetext" moz-do-not-send="true">maurizio.cimadamore@oracle.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="">No worries.<br class="">
<br class="">
I guess having a look at jfr file would be useful.
But note that I don't think you can send that to the
mailing list - AFAIK, attachments are dropped.<br class="">
<br class="">
Also, forgot to ask - is this something for which
you saw a difference between 18 and 19? Because that
would be odd too.<br class="">
<br class="">
Maurizio<br class="">
<br class="">
On 25/10/2022 13:26, Sebastian Stenzel wrote:<br class="">
<blockquote type="cite" class="">I can't reproduce
it any longer. 😖<br class="">
<br class="">
I swear I would not have consulted the mailing
list, if the observation had not been that spooky.
Especially regarding said discrepency between
`asReadOnlyBuffer()` and `duplicate()`.<br class="">
<br class="">
I still have the .jfr file, though. Is this of any
use (other than proving I'm not seeing ghosts)?<br class="">
<br class="">
<blockquote type="cite" class="">On 25. Oct 2022,
at 13:15, Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" class="moz-txt-link-freetext" moz-do-not-send="true">maurizio.cimadamore@oracle.com</a>>
wrote:<br class="">
<br class="">
<br class="">
On 25/10/2022 12:04, Maurizio Cimadamore wrote:<br class="">
<blockquote type="cite" class="">```<br class="">
public MappedByteBuffer duplicate() {<br class="">
return new DirectByteBuffer(this,<br class="">
this.markValue(),<br class="">
this.position(),<br class="">
this.limit(),<br class="">
this.capacity(),<br class="">
0,<br class="">
<br class="">
fileDescriptor(),<br class="">
isSync(),<br class="">
<br class="">
segment);<br class="">
}<br class="">
```<br class="">
</blockquote>
Btw, the implementation of `adReadOnlyBuffer` is
virtually identical to the above - the only
difference is that
DirectBuffer::asReadOnlyBuffer creates a new
DIrectBufferR (where R stands for Read Only),
not just another DirectBuffer. On read-only
direct buffers (DirectBufferR), asReadOnly
buffer just calls duplicate().<br class="">
<br class="">
So, I think it's very strange that one one of
them misbehave, since the implementation is so
close.<br class="">
<br class="">
What do you use to monitor the allocations? One
theory is that perhaps one version of the code
"escapes" better than the other, so the numbers
you see are skewed, and in some cases you see
the actual BB allocations on the heap, whereas
in the other case you don't see anything because
the JVM scalarizes the BB views. But again, the
`duplicate` and `adreadOnlyBuffer` are so close
to each other that it's hard to imagine
meaningful differences in terms of escape
analysis (even though escape analsyis can
sometimes act in surprising ways).<br class="">
<br class="">
Maurizio<br class="">
<br class="">
</blockquote>
</blockquote>
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