From: Erik Groeneveld <erik@cq2.nl>
To: Andrew Haley <aph@redhat.com>
Cc: java@gcc.gnu.org, "Boehm, Hans" <hans.boehm@hp.com>
Subject: Re: GC leaks debugging
Date: Fri, 08 Apr 2011 15:48:00 -0000 [thread overview]
Message-ID: <BANLkTi=7SEhVZw7b48x46HF9Sv6zWmt4Qw@mail.gmail.com> (raw)
In-Reply-To: <4D9F13E9.7000106@redhat.com>
>> The last good dump I have from the test after 12 million cycles (it
>> then got killed) has nothing like File stuff at all. A also saw other
>> suspicious objects, but they all disappeared later on. The collecter
>> really works wel!
>>
>> Next hypothesis:
>> From analyzing graphs from the logs and comparing them to those of the
>> OpenJDK, I get the feeling that the collector looses control by not
>> collecting often enough.
>>
>> The heap is quite unused/free, and remains so during the process. It
>> seems that at some point, the heap fills up very quickly, and then the
>> collector decides to expand the heap instead of collecting (the
>> algorithm for deciding this seems rather complicated). However, a
>> larger heap also causes the collector to collect less frequently. So
>> the next time the heap fills up rapidly, it again decides to expand
>> the heap, again causing less frequent collections. And so on. I´ll
>> post the graph data in a separate post if you want it.
>
> That makes sense as an explanation.
>
> It looks, then, as though there isn't a leak at all. The collector
> does what it's supposed to do. There is always the risk of this with
> any non-compacting dynamic memory allocator.
Yes, a non-moving collector has its limits, but I have still hope for
improvement.
>> And the next hypothesis:
>> Perhaps the program allocates many different (possibly large) sizes,
>> which remain on the free list, but cannot be used because the next
>> objects requested are slightly bigger. I have to study this somewhat
>> more.
>
> I wonder.
>
>> Just two questions:
>> 1. What is a reasonable number of heap sections? I have 131 here.
>> 2. What is a reasonable number of free lists? I have 60, which have
>> 13,000+ entries.
I found from the code that 60 is the upper bound. And 13,000 seems to
be a lot to me. Altogether, the free space is about 700 Mb, of a 900
Mb heap.
Hans, is there a limit on the length of the free lists?
Adjacent blocks of the same size are coalesced; is there also
coalescing of blocks of different sizes at some point?
I tried a build with with USE_MUNMAP, hoping that would help the
collector clean up free-list, but I am still testing.
> Paging Hans Boehm. can you suggest ways to get the system to GC more
> frequently? Would doing so avoid this scenario?
>
> Andrew.
>
next prev parent reply other threads:[~2011-04-08 15:48 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-01 8:39 Erik Groeneveld
2011-04-01 8:45 ` Andrew Haley
2011-04-01 9:03 ` Erik Groeneveld
2011-04-01 9:34 ` Andrew Haley
2011-04-02 0:27 ` Boehm, Hans
2011-04-02 9:39 ` Erik Groeneveld
2011-04-03 17:15 ` Erik Groeneveld
2011-04-03 18:00 ` Erik Groeneveld
2011-04-04 8:13 ` Andrew Haley
2011-04-04 8:53 ` Erik Groeneveld
2011-04-04 9:48 ` Andrew Haley
2011-04-05 4:44 ` Boehm, Hans
2011-04-05 8:58 ` Andrew Haley
2011-04-05 6:50 ` Erik Groeneveld
2011-04-05 9:02 ` Andrew Haley
2011-04-05 12:02 ` Erik Groeneveld
2011-04-05 12:55 ` Andrew Haley
2011-04-06 14:30 ` Erik Groeneveld
2011-04-06 18:33 ` Andrew Haley
2011-04-06 18:39 ` David Daney
2011-04-07 17:43 ` Erik Groeneveld
2011-04-08 8:12 ` Erik Groeneveld
2011-04-08 13:56 ` Andrew Haley
2011-04-08 15:35 ` David Daney
2011-04-08 15:53 ` Erik Groeneveld
2011-04-08 15:57 ` Andrew Haley
2011-04-08 15:48 ` Erik Groeneveld [this message]
2011-04-09 1:17 ` Boehm, Hans
2011-04-09 8:47 ` Andrew Haley
2011-04-09 10:56 ` Erik Groeneveld
2011-04-10 11:03 ` Erik Groeneveld
2011-04-12 18:43 ` Erik Groeneveld
2011-04-13 8:11 ` Andrew Haley
2011-04-13 12:11 ` Bryce McKinlay
2011-04-13 14:27 ` Andrew Haley
2011-04-14 8:36 ` Erik Groeneveld
2011-04-14 8:43 ` Andrew Haley
2011-04-14 10:02 ` Erik Groeneveld
2011-04-14 10:50 ` Andrew Haley
2011-04-15 7:32 ` Erik J Groeneveld
2011-04-01 17:41 ` David Daney
2011-04-02 16:21 ` Erik Groeneveld
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