I don't have 'proof' Tomcat is to blame. Hence the question-mark. All I have
managed is narrow it down to this NMT data, which is not very informative. I
hoped anyone could give me an idea how or where to investigate further. Or if
someone had run into this before.
The connector of the webapp uses Http11NioProtocol. My understanding is it uses
direct-byte-buffers backed by native memory for the Nio channels. I don't know
for sure if that gets allocated through a JNI call, but that was my assumption.
I did not consider trying Mission Control or jvisualvm. Isn't Mission Control
for embedded Java? And AFAIK, jvisualvm is for profiling Java memory usage and
underneath uses tools like jmap, jstat and jcmd. Through GC logs and jmap
heap-dumps I can confidently say there's no memory leak on the Java side. The
NMT data shown comes from jcmd. No type grows beyond control and full GC always
returns to the same baseline for the heap. Anyway, the Java heap is only 360Mb
and this memory-block created by jni_invoke_static has grown to 700Mb by
itself. And I see no out-of-memory messages. The only hint of this happening is
that the RES memory of the Tomcat process keeps growing over time, as shown by
'top'. And it seems GC is getting slower over time, but the customers haven't
noticed it yet. (This is after we switched to ParallelGC. We did see
considerable slow-down when using G1GC in the ref-processing, but we couldn't
figure out why. It would slow to a crawl before the memory leak became obvious.)
Anyway, I was mostly fishing for hints or tips that could help me figure this
out or avoid it.
The application is simple to the point I'm hard-pressed to think of any other
part making JNI calls. The only library I can think of using JNI is
BouncyCastle doing the SSL encryption/decryption, so maybe I'll switch my focus
there.
Thanks for taking the time to think along.
Mark
On 4/4/20, 5:50 AM, "calder" <[email protected]> wrote:
On Fri, Apr 3, 2020 at 8:48 PM Mark Boon <[email protected]> wrote:
>
> For the past few months we’ve been trying to trace what looks like
gradual memory creep. After some long-running experiments it seems due to
memory leaking when
> jni_invoke_static(JNIEnv_*, JavaValue*, _jobject*, JNICallType,
_jmethodID*, JNI_ArgumentPusher*, Thread*) is invoked. Somewhere.
>
> My environment is Tomcat running a proxy webapp. It does TLS termination,
authentication and then forwards the call to local services. It doesn’t do
much else, it’s a relatively small application.
>
> Some (possibly relevant) versions and config parameters:
> Tomcat 8.5
> Java 8u241 (Oracle)
> Heap size = 360Mb
> MAX_ALLOC_ARENA=2
> MALLOC_TRIM_THRESHOLD_=250048
> jdk.nio.maxCachedBufferSize=25600
>
> We couldn’t find any proof of memory leaking on the Java side.
> When we turn on NativeMemoryTracking=detail and we take a snapshot
shortly after starting, we see (just one block shown):
>
> [0x000003530e462f9a] JNIHandleBlock::allocate_block(Thread*)+0xaa
> [0x000003530e3f759a] JavaCallWrapper::JavaCallWrapper(methodHandle,
Handle, JavaValue*, Thread*)+0x6a
> [0x000003530e3fa000] JavaCalls::call_helper(JavaValue*, methodHandle*,
JavaCallArguments*, Thread*)+0x8f0
> [0x000003530e4454a1] jni_invoke_static(JNIEnv_*, JavaValue*, _jobject*,
JNICallType, _jmethodID*, JNI_ArgumentPusher*, Thread*) [clone .isra.96] [clone
.constprop.117]+0x1e1
> (malloc=33783KB type=Internal #110876)
>
> Then we run it under heavy load for a few weeks and take another snapshot:
>
> [0x000003530e462f9a] JNIHandleBlock::allocate_block(Thread*)+0xaa
> [0x000003530e3f759a] JavaCallWrapper::JavaCallWrapper(methodHandle,
Handle, JavaValue*, Thread*)+0x6a
> [0x000003530e3fa000] JavaCalls::call_helper(JavaValue*, methodHandle*,
JavaCallArguments*, Thread*)+0x8f0
> [0x000003530e4454a1] jni_invoke_static(JNIEnv_*, JavaValue*, _jobject*,
JNICallType, _jmethodID*, JNI_ArgumentPusher*, Thread*) [clone .isra.96] [clone
.constprop.117]+0x1e1
> (malloc=726749KB type=Internal #2385226)
>
> While other blocks also show some variation, none show growth like this
one. When I do some math on the number (726749KB - 33783KB) / (2385226 –
110876) it comes down to a pretty even 312 bytes per allocation.
> And we leaked just under 700Mb. While not immediately problematic, this
does not bode well for our customers who run this service for months.
>
> I’d like to avoid telling them they need to restart this service every
two weeks to reclaim memory. Has anyone seen something like this? Any way it
could be avoided?
I'm a bit confused. Your stated title is "JNI Memory Leak?"
Tomcat, to my intimate knowledge, does not use JNI (correct me if I'm rwong)
( quick check
user@stimpy:~/Desktop/tomcat-source/apache-tomcat-8.5.53-src> find .
-name *.c -ls
user@stimpy:~/Desktop/tomcat-source/apache-tomcat-8.5.53-src> find .
-name *.cpp -ls
user@stimpy:~/Desktop/tomcat-source/apache-tomcat-8.5.53-src> find .
-name *.asm -ls
user@stimpy:~/Desktop/tomcat-source/apache-tomcat-8.5.53-src> find .
-name *.pas -ls
}
a) for the "snapshots" provided, there is NO reference to their
association, ie, "what" code are those related to?
b) could you run Mission Control or jvisualvm to locate a stack trace for
this?
We have two apps that use JNI and run via Tomcat (and another app
server) - one is "so old" that it is limited to 32-bit ..... the one
memory leak we have encountered was related to the "native side" (for
us, the native-compiled Pascal side of things (we also use Assembly
code) via Java's JNI code).
So, ultimately, I'm confused why we think Tomcat is "to blame" as
there is no evidence it uses JNI.
It's my experience JNI memory issues are related to the Java JNI or
proprietary native code.
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