<div dir="ltr">Hi Stefan<div class="gmail_extra"><br><div class="gmail_quote">On Wed, Oct 11, 2017 at 2:43 PM, Stefan Johansson <span dir="ltr"><<a href="mailto:stefan.johansson@oracle.com" target="_blank">stefan.johansson@oracle.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<tt>Hi Thomas,</tt><span class=""><br>
<br>
<div class="m_-4568199977031761021moz-cite-prefix">On 2017-10-11 14:16, Thomas Stüfe
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi Stefan,
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Oct 11, 2017 at 1:52 PM,
Stefan Johansson <span dir="ltr"><<a href="mailto:stefan.johansson@oracle.com" target="_blank">stefan.johansson@oracle.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi Thomas,<br>
<br>
Seems like you found a bug here. As you say, for G1 the
"commit watermark" doesn't really make sense, because we
can have regions uncommitted in the middle of the heap. I
think we print the value to look similar to the other
heaps/GCs. The bug here is that we don't multiply with the
region size, but just add it. So we should change the row
in question to:<br>
p2i(_hrm.reserved().start() + (_hrm.length() *
HeapRegion::GrainWords)),<br>
<br>
This would give a better value. It would not be the whole
truth, since there might still be objects above this
address if we have uncommitted regions in the heap. I
better value might be "highest region committed" * "heap
region size", but that would lie because not all memory
below that has to be committed.<br>
<br>
I created a bug for this:<br>
<a href="https://bugs.openjdk.java.net/browse/JDK-8189169" rel="noreferrer" target="_blank">https://bugs.openjdk.java.net/<wbr>browse/JDK-8189169</a><br>
<br>
</blockquote>
<div><br>
</div>
<div>Thank you for taking a look.</div>
<div><br>
</div>
<div>Would it not make more sense to just omit the middle
address value then for g1? <br>
</div>
</div>
</div>
</div>
</blockquote></span>
Yes, that might actually make most sense. <br><span class="">
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div><br>
</div>
<div>If I understand HeapRegionManager::commit_<wbr>regions() /
uncommit_regions() correctly, comitted and uncomitted
regions can freely interleave, and _hrm.length() is just a
counter, not an address range. So we would print a
theoretical address value - the end of the committed
memory if all regions were located consecutively. But how
useful could that be? </div>
<div><br>
</div>
<div>When I look at the commit boundary value in hs-err
files, I usually do this to check if a heap pointer points
into valid memory or into uncomitted memory. For that, I
would prefer the value to be exact or not be there.</div>
<div><br>
</div>
</div>
</div>
</div>
</blockquote></span>
I agree, this was the part about "not the whole truth". And I agree
with you, the best way is probably to just remove it. I never use
this value for G1, I always look at the region table to check if
pointers are valid or not.<br>
<br></div></blockquote><div><br></div><div>Good Point, there is that. Thank you!</div><div>..Thomas</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF">
Thanks,<br>
Stefan<span class=""><br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div>Thanks, Thomas</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
Cheers,<br>
Stefan
<div class="m_-4568199977031761021gmail-HOEnZb">
<div class="m_-4568199977031761021gmail-h5"><br>
<br>
<br>
On 2017-10-11 12:48, Thomas Stüfe wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
Hi all,<br>
<br>
In a customer error file I found the following
output:<br>
<br>
Heap:<br>
garbage-first heap total 2592768K, used 1914672K
[0x0000000679000000, 0x0000000679104f20,
0x00000007f0000000).<br>
<br>
I wonder about the middle address value
(0x0000000679104f20). I was assuming this to be the
commit watermark. But the value seemed awfully low -
just ~1MB beyond the start address of the reserved
area. Given that about 4/5th of the heap is in-use,
this seemed odd.<br>
<br>
Looking at the code:<br>
<br>
void G1CollectedHeap::print_on(outp<wbr>utStream*
st) const {<br>
....<br>
st->print(" [" PTR_FORMAT ", " PTR_FORMAT ", "
PTR_FORMAT ")",<br>
p2i(_hrm.reserved().start()),<br>
>> p2i(_hrm.reserved().start() +
_hrm.length() + HeapRegion::GrainWords), <<<br>
p2i(_hrm.reserved().end()));<br>
...<br>
}<br>
<br>
I am still confused. What is
"_hrm.reserved().start() + _hrm.length() +
HeapRegion::GrainWords"? We add the number of
comitted heap regions to the start address, plus the
size of one heap region in words? Sorry, I am not a
GC expert, could someone clarify what this address
is?<br>
<br>
Another question, while looking further into how g1
commits memory I looked at G1PageBasedVirtualSpace
and it seems to me that there is no clear commit
water mark because pages do not have to be committed
sequentially, is that correct?<br>
<br>
Thanks for clarifying!<br>
<br>
Kind Regards, Thomas<br>
</blockquote>
<br>
</div>
</div>
</blockquote>
</div>
<br>
</div>
</div>
</blockquote>
<br>
</span></div>
</blockquote></div><br></div></div>