RFR 8234270: [REDO] JDK-8204128 NMT might report incorrect numbers for Compiler area
Thomas Stüfe
thomas.stuefe at gmail.com
Mon Nov 25 20:54:48 UTC 2019
Hi Zhengyu,
Hi Zhengyu,
http://cr.openjdk.java.net/~zgu/JDK-8234270/webrev.00/src/hotspot/share/memory/arena.cpp.udiff.html
not sure I understand this change - why is it needed?:
@@ -360,11 +360,12 @@
}
if (k) k->set_next(_chunk); // Append new chunk to end of linked list
else _first = _chunk;
_hwm = _chunk->bottom(); // Save the cached hwm, max
_max = _chunk->top();
- set_size_in_bytes(size_in_bytes() + len);
+ size_t new_size = size_in_bytes() + _chunk->length();
+ set_size_in_bytes(new_size);
void* result = _hwm;
_hwm += x;
return result;
}
http://cr.openjdk.java.net/~zgu/JDK-8234270/webrev.00/src/hotspot/share/services/mallocTracker.hpp.udiff.html
- inline void resize(long sz) {
+ inline void resize(ssize_t sz) {
if (sz != 0) {
+ assert(sz >= 0 || _size >= size_t(-sz), "Must be");
Atomic::add(size_t(sz), &_size);
DEBUG_ONLY(_peak_size = MAX2(_size, _peak_size);)
}
}
assert looks fine but the Atomic::add() took me by surprise: when size is
reduced, we feed it knowingly a negative number we then to unsigned and
rely on the overflow? Just a nit, but would Atomic::sub() not be clearer
here?
http://cr.openjdk.java.net/~zgu/JDK-8234270/webrev.00/test/hotspot/jtreg/runtime/NMT/HugeArenaTracking.java.html
The test is fine as it is. Some thoughts (feel free to ignore them):
- would be more interesting to shake the boat a little by varying increase
rate, e.g.:
60 // Allocate 2GB+ from arena
61 long total = 0;
62 while (total < 2 * GB) {
long increase = <random_number_between_some_bytes_and_I dont
know, 100M? Capped at 2 GB>
63 wb.NMTArenaMalloc(arena1, increase);
64 total += increase;
65 }
and maybe test jcmd VM.native_memory before this point? I know its annoying
since the numbers are probably not exact, and parsing would be necessary.
Just an idea.
66 wb.NMTFreeArena(arena1);
On Mon, Nov 25, 2019 at 2:30 PM Zhengyu Gu <zgu at redhat.com> wrote:
> Ping ... May I get a second review?
>
> Thanks,
>
> -Zhengyu
>
> On 11/21/19 12:12 PM, yumin qi wrote:
> > Hi, Zhengyu
> >
> > The fix looks good to me.
> >
> > Thanks
> > Yumin
> >
> >
> >
> > On Wed, Nov 20, 2019 at 5:49 AM Zhengyu Gu <zgu at redhat.com
> > <mailto:zgu at redhat.com>> wrote:
> >
> > JDK-8204128 did not fix the original bug. But new assertion helped to
> > catch the problem, as it consistently failed in Oracle internal
> tests.
> >
> > The root cause is that, when NMT biases a resource area to compiler,
> it
> > did not adjust tracking data to reflect that. When the biased
> resource
> > area is released, there is a possibility that its size is greater
> than
> > total size recorded, and underflow a size_t counter.
> >
> > JDK-8204128 patch also missed a long to ssize_t parameter type
> change,
> > that resulted new test failure on Windows, because long is 4-bytes on
> > Windows.
> >
> > Many thanks to Leonid Mesnik, who helped to run this patch through
> > Oracle's internal stress tests.
> >
> > Bug: https://bugs.openjdk.java.net/browse/JDK-8234270
> > Webrev:
> http://cr.openjdk.java.net/~zgu/JDK-8234270/webrev.00/index.html
> >
> >
> > Test:
> > hotspot_nmt
> > Submit test
> > Oracle internal stress tests.
> >
> >
> > Thanks,
> >
> > -Zhengyu
> >
>
>
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